GEOPHILOMORPHA

Koch, Markus & Edgecombe, Gregory D., 2012, The preoral chamber in geophilomorph centipedes: comparative morphology, phylogeny, and the evolution of centipede feeding structures, Zoological Journal of the Linnean Society 165 (1), pp. 1-62 : 5-36

IN GEOPHILOMORPHA

Mecistocephalidae

Epipharynx: The labrum has a mid-piece tooth that forms the apex of a short, strongly sclerotized, darkbrown median tooth plate on the labral part of the epipharynx in all studied species ( Figs 2A , 3 ). The adjacent edges of the labral side-pieces are similarly sclerotized and project to different degrees towards the mid-piece tooth, most strongly in Arrup kyushuensis and Tygarrup diversidens ( Fig. 3B ). The border between the labral and clypeal regions is most clearly defined in Dicellophilus carniolensis in which it is marked by a change from pervasive spiniferous scales (on the labral part) to a smooth surface (on the clypeal part) ( Fig. 3A ), as well as by a well-defined, medially interrupted transverse stripe of pigmentation along the proximal edge of the labral part that fades out medially ( Figs 2A , 3A ). In contrast to a pervasively scaly labral surface in Dicellophilus and pervasive covering by slender needle-like spines in Mecistocephalus sp. from Lord Howe Island (see Fig. 5A ), the labral part of the epipharynx of Tygarrup diversidens and Mecistocephalus tahitiensis is completely smooth apart from paired longitudinal bands of simple spines medially ( Fig. 3B ). In Arrup kyushuensis , paired bands of slender, antero-medially directed spines originate on each side of the labral tooth plate and converge to form a continuous broad median band of spines ( Fig. 3C ).

Several rows of spiniferous scales form paramedian bands on the labral part in Dicellophilus ( Fig. 4A ); they differ from the scales covering the internal face of the labral side-pieces in that the spines increasingly elongate towards the midline and are medially directed (versus anteriorly on the side-pieces). In Mecistocephalus sp. from Lord Howe Island ( Fig. 5A ), the needle-like spines covering the entire inner labral surface barely increase in length towards the midline but increasingly change their orientation from an anterior to a medial direction. In all species studied, the labral spine bands continue onto the clypeal part of the epipharynx, either as an unpaired median band of spiniferous scales or simple spines ( Dicellophilus , Arrup : Fig. 3A, C , respectively), or as paired bands of simple spines that only proximally unite as an unpaired band ( Tygarrup diversidens , Mecistocephalus tahitiensis : Fig. 3B ), or as a field of spines that covers the entire surface of the clypeal part ( Mecistocephalus sp. : Fig. 5A ). The orientation of the spines on the clypeal part also varies, the tips of the spines being directed either antero-mesially ( Dicellophilus , Mecistocephalus sp. : Fig. 4B ) or posteriorly towards the mouth ( Arrup , Tygarrup , Mecistocephalus tahitiensis : Fig. 4C–E ). In the latter case, the median band broadens proximally due to converging lateral spine fields that unite with the median band immediately in front of the mouth. The shape of the spines is largely uniform along the length of the clypeal part except for Mecistocephalus sp. , in which the spines proximally shorten and broaden, thereby forming a transverse band of conical tubercles in front of the mouth ( Fig. 5A ).

The clypeal part of the epipharynx of all examined species of Mecistocephalidae bears a kind of sensilla that is not observed on the corresponding region (or elsewhere on the epipharynx) in any other Geophilomorpha (or indeed Chilopoda as a whole). Each consists of a slightly elevated circular structure in which a central sensillum that bears a terminal pore is surrounded by short spines (see description of character 73 below) ( Fig. 4F ). The precise numbers and geometries of the sensilla clusters vary between taxa. In Dicellophilus carniolensis , a median cluster of seven sensilla is present without separation into obvious groups ( Fig. 4B ); in Mecistocephalus tahitiensis ( Fig. 4D ), Arrup kyushuensis ( Fig. 4C ), and Tygarrup diversidens ( Fig. 4E ) the cluster is distinctly broken up into lateral clusters of two or three sensilla ( Fig. 4F ) and a single median sensillum lying posterior to the lateral clusters. In Mecistocephalus sp. from Lord Howe Island the entire grouping is arranged more or less transversely ( Fig. 5A ), composed of a single sensillum medially and a scattered pair of sensilla more laterally.

Hypopharynx: Compared with that of many other Geophilomorpha , the hypopharynx of Mecistocephalidae is relatively broad and flat ( Figs 2C, D , 6A–C ). Its frontal surface has spines or branching scales confined to a band along paired lips bordering a mesial longitudinal groove. The range of variation observed runs from Tygarrup and Arrup , which have simple spines restricted to the lips on the proximal part of the hypopharynx, and the lips along the distal part being devoid of spines ( Fig. 6A ), over Dicellophilus , in which the entire length of the lips bears dense spine clusters that continue onto the distal tip of the hypopharynx ( Fig. 6C, D ), to Mecistocephalus sp. from Lord Howe Island, in which almost the entire frontal surface is covered by simple spines of variable length ( Fig. 5B ). On both the lips and the distal tip, the spine clusters are arranged in small aggregations composed of several spines of varying length and diameter. These groupings can variably be seen to emanate from a common base ( Fig. 6D ), although they are generally not arranged in a plane (as would be the case for scales). The distal tip of the hypopharynx also bears a few conical sensilla that have not been observed to bear a terminal pore ( Fig. 6D, E ).

In all examined species of Mecistocephalidae , the distal part of the hypopharynx is laterally bisected by a pronounced furrow that terminates at a notch in the distal margin ( Fig. 6A , no). Because of the distal lateral notches, the hypopharynx appears to have a tripartite tip, composed of paired shorter lateral lobes and an unpaired, slightly longer and broader median lobe. The furrows between the lateral and median lobes are strengthened by a sclerotized, pigmented bar ( Fig. 2C, D , sf), both furrow and bar being restricted to Mecistocephalidae . The bar is seen in transverse sections of Dicellophilus to be continuous with an unpaired median sclerotized plate defined on the backside of the hypopharynx ( Fig. 8C ). Alongside this median plate and below the lateral lobes lie the slit-like openings of the paired hypopharyngeal glands. The backside of the hypopharynx contrasts with the frontal surface in being mostly smooth, lacking both spines and sensilla ( Fig. 6B ).

Mandible: The mandibles of Tygarrup ( Fig. 7A ), Arrup ( Fig. 7B ), and Mecistocephalus tahitiensis are similar in gross morphology and contrast markedly with those of Dicellophilus ( Fig. 7C–E ). The former type of mandible has long pectinate lamellae (each with up to 20 teeth) developed along a gnathal edge that occupies almost the entire mesial margin of the gnathal lobe, and has a hump-like, strongly protruding, and more or less pointed condyle on the dorsolateral surface of the gnathal lobe ( Fig. 7A ). The mandible of Dicellophilus carniolensis has a relatively shorter gnathal edge, composed of fewer (3–5 fide Bonato et al., 2010b; four in Fig. 7D ) shorter pectinate lamellae, has a strengthened pointed cone (‘translucent tooth’ fide Eason, 1964) in front of the proximalmost pectinate lamella, an inconspicuous, more elongate ridge-like condyle ( Figs 7C , 8A ), and an expansive pad-like field of dense spines occupying its entire ventro-lateral outer surface ( Fig. 7E ). The spines on the proximal part of the pad are broadbased and bear paired rows of short spinules along their distal extent ( Fig. 7C , inset) but abruptly change to longer simple spines on the distal part of the pad. A combination of both morphologies is shown by the mandibles of Mecistocephalus sp. from Lord Howe Island, which has a relatively long gnathal edge with about ten short pectinate lamellae (each with up to ten teeth) with an inconspicuous ridge-like condyle and a pad-like field of spines on the outer surface of the gnathal lobe ( Fig. 5C ). In contrast to the state in Dicellophilus , the spines encompass the entire gnathal edge of Mecistocephalus sp. , including its inner mesial margin ( Fig. 5D ), and extend onto the bases of the pectinate lamellae.

Irrespective of their variable number and size, the pectinate lamellae are always arranged in an imbricate series, along which the size of the lamellae increases from both distal and proximal towards the middle of the series (i.e. the proximalmost and distalmost lamellae are the shortest along the series, while the longest are found in the middle of the gnathal edge). All pectinate lamellae are translucent or light brownish in the species studied except for the mandibles of Mecistocephalus sp. from Lord Howe Island. In this species, the proximal pectinate lamellae show increasing pigmentation, gradually turning from light brown to dark brown; the pectinate lamella closest to the mouth ( Fig. 5C, D , dl) is the darkest and apparently most strongly sclerotized, similar to the so-called ‘dentate lamella’ in Himantariidae . In Tygarrup , the few teeth of the proximalmost comb also markedly differ in their broader size from the more tiny teeth of the remaining lamellae ( Fig. 7A ; see also Bonato et al., 2003: fig. 10A), but they hardly appear to be more robust (i.e. more sclerotized).

Tentorium: Previous descriptions of the ‘fulcrum’ in mecistocephalids are restricted to its exoskeletal components. A more complete picture of the tentorium, including its endoskeletal parts, is now available for Dicellophilus carniolensis . The exoskeletal components correspond neatly in position to the epipharyngeal bar, transverse bar, and hypopharyngeal bar of nongeophilomorph centipedes, but they are much more slender in mecistocephalids ( Fig. 2B ). In contrast to the state in Adesmata, the epipharyngeal bar has a submarginal position on the epipharynx below the labral side-pieces. Externally, the epipharyngeal bar provides a sclerotized groove for the articulation with the mandibular condyle ( Fig. 8A ). Internally, the epipharyngeal bar forms an endoskeletal ridge all along its length (‘fp’ in Fig. 8A ; ‘mb’ in Fig. 8B ) that continues towards the hypopharyngeal bar up to the posterior tip of the anterior tentorial apodeme (‘pp’ in Fig. 8C ) (‘posterior process’ fide Manton, 1965; Koch, 2003). Anteriorly, the endoskeletal ridge continues over the apex of the epipharyngeal bar as a frontal process. At the level of the mandibular articulation, two muscles attach to the base of the frontal process: a longitudinal muscle arising from the clypeus ( Fig. 8A, t 1 ), and a transverse muscle (t2) arising laterally from the dorsal head capsule. The position of the latter muscle indicates that its contraction causes tentorial movements that contribute to the abduction of the mandibular gnathal lobe via its articulation with the epipharyngeal bar. No corresponding muscle has yet been described for adesmatan geophilomorphs.

The transverse bar extends towards the cephalic pleurites, which in mecistocephalids form undivided ‘buccae’ (fide Crabill, 1959). The sclerotized parts of the transverse bar form a slender, darkly pigmented stripe that laterally arches forwards, its apex pointing in between the lateral margin of the labral sidepiece and the tip of the stilus ( Fig. 2B ). In contrast to the state in non-geophilomorphs (see, for example, Applegarth, 1952; Manton, 1964, 1965), no muscles attach to the transverse bar in Dicellophilus .

The hypopharyngeal bar is a broad and flat sclerite that does not give rise to endoskeletal formations. It extends along the lateral margin of the hypopharynx towards the tip of its lateral lobes, without showing any sclerotic connection to the sclerotized bars of the longitudinal furrows separating the lateral lobes from the median distal tip of the hypopharynx ( Fig. 2C ). Basally the hypopharyngeal bars provide articular support for the mandibular gnathal lobe ( Fig. 8B ), as is the case in non-geophilomorph centipedes ( Manton, 1965).

The epi- and hypopharyngeal bars unite next to the mouth opening and protrude into the head lumen to form an oblique plate-like apodeme ( Fig. 8C , pp) (‘posterior process’ of the tentorium fide Manton, 1965) that serves as the origin and insertion for a variety of muscles, the details of which remain to be worked out. The paired apodemes are not interconnected by a ligamentous bridge, which in non-geophilomorphs is formed by the connective tendons of the mandibular and maxillary segments.

Himantariidae

Epipharynx: The labral part of the epipharynx is smooth in all examined species ( Fig. 9A, D ). Labral marginal denticles vary in size and number, and for the three species studied here have been accurately illustrated by Chalande & Ribaut (1909: figs 18, 20, 45). The border between the labral and clypeal parts of the epipharynx is indicated by the limits of a field of strong spines that cover the entire surface of the clypeal part. These spines are simple (not grouped at their bases or arranged as scale-like rows) and of variable density, being sparser in Bothriogaster signata ( Fig. 9D ) than in Haplophilus subterraneus ( Fig. 9A ) or Himantarium gabrielis . In the latter two taxa, adjacent spines are so crowded as to be in contact at their bases ( Fig. 9F ). The apices of these spines are directed proximally (i.e. towards the mouth) along the midline and proximo-medially more laterally. The mesial region of the clypeal part bears numerous sensilla coeloconica, scattered over a substantial area without regular arrangement ( Fig. 9D ). The sensilla taper to a bluntly pointed apex but a terminal pore is not obvious ( Fig. 9E ), and they are surrounded by a narrow circular rim. In Himantarium and Haplophilus , the socket surrounding the sensilla coeloconica is encircled by short spines, some of which form branching groups ( Fig. 9F ). As defined by the field of spines and bottleshaped sensilla, the clypeal part of the epipharynx has a curved distal margin that encroaches upon the labral part of the epipharynx medially, i.e. the labral part is shortened medially. At the lateral edge of the field of spines are several spear-shaped sensilla. This group of sensilla is either set amidst the field of spines ( Haplophilus : Fig. 9B , arrows) or is lateral to the spine field ( Himantarium : Fig. 9G ). The spearshaped sensilla have a slender, weakly tapering terminal part and a broad, dome-shaped base ( Fig. 9B, G ). They evidently lack terminal pores, none being visible in any of the three sampled species.

A paired opening on the proximo-lateral clypeal part of the epipharynx in Haplophilus ( Fig. 9A ) and Himantarium is presumed to represent the buccal gland opening (‘glandulae buccales mediales’; Fahlander, 1938).

Hypopharynx: The himantariid hypopharynx is short and markedly convex along its frontal surface ( Fig. 10A ). The hypopharyngeal bar extends as a broad flap along the length of the hypopharynx, with the opening of the hypopharyngeal gland (= glandula mandibularis fide Fahlander, 1938), a lengthy slit with a subvertical orientation at the distal end of the flap ( Fig. 10C ). Most of the frontal surface is smooth, spines being confined to the median lips and the proximal margin. All three studied himantariid species have robust spines on the proximal medial part of the hypopharynx, their morphology and orientation being similar to those on the pharynx. In Bothriogaster signata the hypopharyngeal and pharyngeal spines are of comparable density whereas the hypopharyngeal spines of Himantarium gabrielis and Haplophilus subterraneus are densely crowded both proximally ( Fig. 10B ) and along the median lips ( Fig. 10C ). All of these spines have their apices pointed proximally or proximo-medially. The median lips bear scattered conical sensilla ( Fig. 10E, F ) that project from a rounded socket and are surrounded by a narrow circular rim that is itself delimited by a shallow furrow ( Fig. 10D ). The median incision terminates on the backside of the hypopharynx, and a broad extent of the backside is an area of smooth cuticle that is completely undivided ( Fig. 10E ). In Haplophilus subterraneus the distal part of the median incision is fringed by a field of scales that each bears several short spines along its proximal margin ( Fig. 10E ).

Mandible: All studied species have the lamina condylifera delimited by a strong suture ( Fig. 11A, B ) and the condyle is prominent and recurved at its tip (hook-like). The structure of the gnathal edges of the mandibles of taxa studied herein was depicted accurately by Chalande & Ribaut (1909). Their descriptions of variability in the structure and numbers of pectinate lamellae and tooth numbers on the lamellae are corroborated by SEM imagery. All species depict a widening of the lamellae from distal to proximal. The distal pectinate lamella bears only a few teeth ( Fig. 11A ), the numbers rapidly increasing and then slightly decreasing in more proximal lamellae (e.g. 4, 14, 28, 34, and 29 teeth in the five lamellae of the studied specimen of Himantarium gabrielis excluding the strongly sclerotized proximal lamella). The observed maximum number of teeth in the examined mandibles of Bothriogaster signata is 23, in Haplophilus subterraneus 13. In our material, the number of teeth in the most proximal lamella (‘dentate lamella’ of previous authors; dsl in Fig. 11 ) is seven in Haplophilus subterraneus , ten in Himantarium gabrielis , and 13–14 in Bothriogaster signata . In all species, this lamella is differentiated from the others by a markedly enhanced degree of sclerotization.

Oryidae

Epipharynx: The labral marginal spines of oryids correspond to previous descriptions in the taxonomic literature. Orya almohadensis ( Fig. 12A ) has small, closely arranged tooth-like spines on the intermediate part that grade into longer, more slender, and more medially pointing spines on the lateral parts. As observed by Turk (1955), the longer lateral spines do not show an alternation with shorter spines as is known for O. barbarica ( Attems, 1928: text-fig. 23). The most medial spines have blunt apices, the total number of spines being 60. In Notiphilides maximiliani the median spines are longer than those of Orya and c. 90 spines fringe the labral margin.The limits of the labral and clypeal parts are identified following the criteria used above in Himantariidae , the labral part being reduced distomedially to a short, smooth extent. The clypeal part is delimited by the presence of two kinds of sensilla (as in Himantariidae ). The median region bears sensilla coeloconica (40 in Orya almohadensis ) scattered over a large area. These sensilla are set in shallow, circular sockets ( Fig. 12A , upper inset). In contrast to those in Himantariidae , the sensilla coeloconica are mostly surrounded by smooth cuticle, with at most just a few spines amongst the sensilla field, the apices of these spines consistently directed mesially. Distal to the field of sensilla coeloconica are small, mesially directed spines in a spine field that spans the medial and lateral parts of the epipharynx; because the morphology and orientation of these spines are the same as those among the sensilla coeloconica, the spine field is identified as belonging to the clypeal rather than the labral part of the epipharynx. At the edge of the field of sensilla coeloconica are many spear-shaped sensilla ( Fig. 12A , lower inset) that, like those in the corresponding position in Himantariidae , are slender and tapering along most of their length, with a broadened, dome-shaped base ( Fig. 12C ). A terminal pore has not been detected in the spear-shaped sensilla. The spearshaped sensilla are either confined to the proximolateral part of the epipharynx ( Orya : Fig. 12A ) and are replaced by the sensilla coeloconica mesially, or are present on the median clypeal part as well ( Notiphilides : Fig. 12B ). In O. almohadensis 23–28 spear-shaped sensilla are present on each side of the epipharynx in the figured specimen. The relatively narrow epipharynx of Notiphilides shows a marked median longitudinal ridge along the entire clypeal part ( Fig. 12B ). A median ridge is also observed in the other sampled oryids, but it is less pronounced and mostly restricted to the distal clypeal part ( Fig. 12A ).

Hypopharynx: The oryid hypopharynx is relatively flat and at least moderately tapering distally ( Fig. 13A, D ). The proximal part of the frontal surface has a field of spear-shaped sensilla on each side ( Fig. 13B ), their morphology being identical to the spear-shaped sensilla on the proximo-lateral part of the epipharynx described above. In O. almohadensis some 30 spear-shaped sensilla are present on each side. Spines are lacking along most of the length of the lips and on nearly all of the frontal surface of the hypopharynx, but are instead concentrated on the distal tip, where they form a dense mass of triangular, flattened spines with their apices directed mesially. The backside of the hypopharnyx in entirely undivided, with conical sensilla scattered over much of its surface ( Fig. 13C–E ). Each sensillum has a circular rim of similar diameter to the sensillum at its base. Proximally the paired openings of the hypopharyngeal gland (ohg in Fig. 13C, D ) form pronounced slits below the base of the hypopharynx, oriented obliquely to the horizontal plane (i.e. less vertically oriented than in Himantariidae ).

Mandible: Oryid mandibles have a variable number of pectinate lamellae. By analogy to Mecistocephalidae , numbers of lamellae and teeth on the lamellae are presumed to increase ontogenetically ( Demange, 1968: 291; Bonato et al., 2003: 566). Of species sampled here, pectinate lamellae number six in N. maximiliani ( Fig. 14A ), seven in O. almohadensis ( Fig. 14B–D ), and four in Orphnaeus brevilabiatus ; Attems (1929) indicated a range of intraspecific variation in O. barbarica from five to eight lamellae. Those situated distally in the series have only a few teeth ( Fig. 14D ), whereas the longer pectinate lamellae have 14–22 teeth. The most proximal lamella may have slightly more robust teeth (11–18 in the species examined here) than the others ( Fig. 14B ), but it does not differ in pigmentation and sclerotization from remaining lamellae. The most distal lamella is ventrally followed by a row or cluster of tooth-like spines formed by the sharply angled ventral margin of the gnathal lobe ( Fig. 14C, D , vm). In Orphnaeus brevilabiatus these spines resemble the teeth of the pectinate lamellae in size and shape; in O. almodahensis they are distinguished by shorter length and a distinct broadened base. The lamina condylifera is hardly pigmented in Orphnaeus brevilabiatus and N. maximiliani and never delimited by a suture from remaining parts of the gnathal lobe; in all species studied it bears a robust, brownish-sclerotized hookshaped condyle ( Fig. 14A, B , co).

Schendylidae

Epipharynx: Schendylidae have no trichomes on the labral part of the epipharynx but display a dense field of branching spines on the clypeal part ( Fig. 15A, G ). As in himantariids and oryids, the border between labral and clypeal parts is strongly arched as the labral part is very narrow medially, in accordance with the absence of a sclerotic labral mid-piece. The margin of the labral side parts is equipped with sharp denticles of variable size and strength; medially, between the side-pieces, the marginal denticles turn into more blunt teeth (e.g. Plesioschendyla confossa : Fig. 15A ) or into an even arc that bears a few swellings (e.g. Hydroschendyla submarina : Fig. 15G ; ‘larges callosités’ of Brölemann & Ribaut, 1912: 137). The spines of the clypeal part are laterally arranged as scale-like bands, each composed of several slender spines ( Fig. 15H ). In Pectiniunguis argentinensis the scale-like aggregation of the spines is discernable even in the median part of the field ( Fig. 15D–F ), whereas in other taxa, the spines are so densely clustered that the individual scale-like aggregations are indistinct. Bottle-shaped sensilla coeloconica are found amidst the spine field ( Fig. 15G , sc). They are arranged as single median sensilla and pairs of sensilla that are slightly to distinctly offset from strict bilateral symmetry, numbering four sensilla in Pectiniunguis , six in Hydroschendyla , and eight in Plesioschendyla . A terminal pore can be recognized in these sensilla in some instances, such as in Pectiniunguis ( Fig. 15E ), although often it is indistinct. On the proximo-lateral clypeal part of the epipharynx, at the outer edge of the field of branching spines, is a cluster of spear-shaped sensilla ( Fig. 15B , sp), the morphology of which is as described above for Himantariidae , i.e. they have a tapering terminal part that originates from broader, dome-shaped base ( Fig. 15B, F, H ). Each lateral cluster consists of up to 18 spearshaped sensilla ( Fig. 15F ).

Hypopharynx: The schendylid hypopharynx strongly tapers distally ( Fig. 16A ), with a somewhat flattened frontal surface. A mesial longitudinal groove on the frontal surface is bordered by paired lips bearing a few rows of scale-like, mesially directed spines. Towards the hypopharyngeal tip the spines gradually increase in number and size ( Fig. 16E ). The frontal groove continues onto the backside of the hypopharynx as a median incision, such that the hypopharynx appears to be almost entirely divided into two, except for its proximal base. A lateral cluster of three or four spear-shaped sensilla is present on each lip of the hypopharynx in Hydroschendyla , confined to the proximalmost part of the lips ( Fig. 16F ). The hypopharyngeal glands have large paired dorsoventrally compressed ducts ( Fig. 8G ) that open basally on the backside of the hypopharynx via elongate, slit-like openings ( Fig. 16E , ohg).

Mandible: The mandibular gnathal edge of schendylids is composed of two pectinate lamellae ( Fig. 17C–G ). The two lamellae are arranged in a single row but are weakly to sharply angled against each other and may show a slight degree of overlap, as in Hydroschendyla . The proximal lamella (dentate lamella in previous morphological descriptions) bears thick, strongly sclerotized teeth that gradually increase in length from proximal to distal; in the sampled specimens they number seven in Plesioschendyla ( Fig. 17D, E ), 12 in Hydroschendyla ( Fig. 17C ), and 13 in Pectiniunguis ( Fig. 17F, G ). In the latter two, the teeth are subdivided into three groups, the proximalmost comprising six or seven teeth, the other two groups having three teeth each. Two groups of teeth (rather than three) are exceptionally observed in both Hydroschendyla submarina and Pectiniuguis argentinensis ; see Brölemann & Ribaut 1912, and Pereira & Coscarón, 1976, respectively, for infraspecific variation). The distal lamella bears multiple (16–29) hyaline teeth that are readily distinguishable from those of the proximal lamellae in being longer and more slender. The condyle of the mandibular gnathal lobe is hook-shaped in all sampled species, the lamina condylifera being delimited by a suture in Pectiniunguis and Hydroschendyla , but not in Plesioschendyla ( Fig. 17D ).

Tentorium: The descriptive account provided here is based on Hydroschendyla submarina . Exoskeletal sclerites continuous with the endoskeletal anterior tentorial apodeme extend from the origin of this apodeme next to the mouth towards the labral sidepiece and the cephalic pleurite as well as onto the hypopharynx in a T-shaped configuration (‘fulcrum’) ( Fig. 2F ). Its apex forms an oblique, slightly arched bar between the labral side-piece and the cephalic pleurite. At its midlength this bar expands into a triangular sclerite that sends off a sclerotized mesial branch interconnecting the hypopharyngeal bar with the oblique bar. The anterior part of the oblique bar resembles the epipharyngeal bar of non-adesmatan centipedes in laterally bordering the clypeal part of the epipharynx and in providing a strengthened mesial ridge to which the condyle of the mandibular gnathal lobe articulates. It differs, however, from the epipharyngeal bar in that it adopts the position of the missing paralabial sclerite, hence showing a marginal (rather than submarginal) position on the epipharynx. The anterior part of the oblique bar further differs from the epipharyngeal bar in non-adesmatan centipedes in that it contributes no endoskeletal formations; a marked frontal process as found in Dicellophilus is absent ( Fig. 8D ). The oblique bar only thickens internally at the level of its triangular expansion, where it forms a short endoskeletal protuberance that might represent a remnant of the frontal process ( Fig. 8E ). A single strand of a longitudinal muscle arising from the clypeus (t 1 in Dicellophilus : Fig. 8A ) attaches to this protuberance, but the greater part of this muscle passes backwards over the triangular expansion and its mesial branch to attach far behind on the posterior process of the tentorium (= anterior tentorial apodeme) (as in Orya barbarica , see Manton, 1965: fig. 81a). Further internal ridges are formed by the vertical orientation of the (exoskeletal) posterior branches of the triangular expansion (i.e. the posterior part of the oblique bar and the mesial branch interconnecting the oblique bar with the hypopharyngeal bar; Fig. 8F : tb, mb). In accordance with the lack (or reduction) of the frontal process, a homologue of the transverse muscle t 2 in Dicellophilus ( Fig. 8A ) seems to be absent in Hydroschendyla (as is the case for Orya barbarica ; see Manton, 1965). In contrast to the state in Dicellophilus , however, a few transverse muscular strands attach further posteriorly onto the mesial branch of the triangular expansion that interconnects the oblique bar with the hypopharyngeal bar ( Fig. 8F ); these strands might represent remnants of muscle t2. Their different point of insertion, far behind the articulation of the mandibles with the fulcrum, renders it unlikely that they cause tentorial movements involved in abducting the mandibular gnathal lobe.

The hypopharyngeal bar expands distally onto the dorso-lateral surface of the hypopharynx in a scoop-shaped manner. Its proximal part unites behind the mouth with the mesial branch of the triangular expansion of the oblique bar of the fulcrum to form an arched, shallow plate-like apodeme ( Fig. 8F ). As in Dicellophilus (and Orya barbarica ; Manton, 1965), the tentorial apodemes are not interconnected by a ligamentous bridge.

Ballophilidae

Epipharynx: The epipharynx of Ballophilus rouxi corresponds in most respects to the description of Schendylidae above. The field of branching spines is concentrated on the median part of the epipharynx with a deep median glabrous area proximally ( Fig. 15C ). The apices of the spines are directed medially in the lateral part of the spine field and proximally in the median part. Bottle-shaped sensilla (sensilla coeloconica; Fig. 15C , sc) amidst the spine field comprise an alternation between a median sensillum and pairs of sensilla that are offset from strict bilateral symmetry, as in Schendylidae , such that a total of six sensilla scattered amidst the field of spines are arranged as 1-2-1-2 (from distal to proximal). On the proximo-lateral part of the epipharynx, outside the field of branching spines, are six or seven spearshaped sensilla on each side ( Fig. 15C , sp). Their structure as conical spines with an inflated base is identical to that seen in Schendylidae .

Hypopharynx: The hypopharynx of Ballophilus rouxi is relatively narrow and deep ( Fig. 16B ), forming a strong arch when viewed from its backside ( Fig. 16D ). The frontal groove continues onto the backside as a deep cleft, which causes the same bipartite appearance of the hypopharynx as in Schendylidae . Scalelike spines with pointed, mesially directed branches are confined to the lips bordering the frontal groove. The spines are slender and very dense, which results in the lips appearing more plumose than in Schendylidae . The number of longitudinal spine rows barely increase towards the hypopharyngeal apex. A field of about 14 spear-shaped sensilla is scattered over a relatively large extent of the proximal part of the hypopharynx, extending near to the lips mesially and almost to the base of the hypopharyngeal bar laterally. The apices of these sensilla are directed proximally ( Fig. 16C ). Like the spear-shaped sensilla on the epipharynx they are composed of a tapering distal part arising from a domed base.

Mandible: The gnathal edge of the mandible of Ballophilus rouxi bears two pectinate lamellae; the more sclerotized one is the dentate lamella of previous descriptions ( Fig. 17A , dl). The more lightly sclerotized lamella has c. 28 teeth in the studied specimens and overlaps about half the length of the more sclerotized lamella. The latter has c. 11 teeth, without subdivision into groups as are seen in most Schendylidae . The mandibular condyle is large and hookshaped ( Fig. 17B , co). Morphology of the gnathal edge appears to be conserved in Ballophilidae (cf. Diplethmus: Ribaut, 1912 : figs 31, 32).

Gonibregmatidae : Gonibregmatus

Epipharynx: The epipharynx of Gonibregmatus anguinus is strongly compressed to a narrow longitudinal bulge, laterally bordered by the large, flat anterior branches of the fulcrum that distally almost meet in the midline ( Fig. 18A ). The distal apex of the epipharynx is formed by a small, triangular, nose-like labrum that lacks both a subdivision into side- and mid-pieces as well as a delimitation of the clypeus ( Fig. 2H ). As depicted by Attems (1929: fig. 295), the labral margin is armed by a fringe of uniformly thick and sharp, strongly sclerotized denticles (inset in Fig. 18A ), directed outwards and backwards. A border between labral and clypeal regions of the epipharynx could not be determined, as the median part of the epipharyngeal bulge was too strongly damaged in the single specimen available for our study. Marginal areas of the epipharynx are devoid of trichomes; their smooth surface distally adopts the surface sculpture of the external face of the clypeolabrum. The proximal area of the epipharyngeal bulge is equipped with a cluster of spear-shaped sensilla ( Fig. 18B ), the tips of which are directed towards the mouth.

Hypopharynx: The outline of the hypopharynx is crudely rhomboid in frontal view ( Fig. 18C ), and the frontal surface is relatively flat ( Fig. 18E ). A broad lateral area has a uniformly smooth surface; this smooth area extends across the midline proximally and has scattered small pores (presumed openings of epidermal glands) on its entire surface. The lips of the hypopharynx bear a distally widening field of dense scales, each branching into a few spines. Scattered amidst these scales, especially towards the frontal groove, are numerous sensilla coeloconica (detail in Fig. 18E ). The backside of the hypopharynx has a complete median incision ( Fig. 18D , mi). The area adjacent to the median incision is a crest bearing branching scales.

Mandible: The gnathal edge of the mandible bears a single pectinate lamella composed of 19 or 20 gently tapering teeth, together with four smaller teeth separated from the larger ones by a narrow diastema ( Fig. 19A ). The outer face of the mandible is ornamented with scutes, those more ventrally bearing a single small denticle at their apices. Neither a condyle nor a suture delimiting a lamina condylifera is observed. The angle delimiting the break between the outer and ventral surfaces of the mandible bears long, slender spines with pointed apices, these spines being developed along most of the length of the mandible. The ventral surface is expanded as a broad, curved field ( Fig. 19B ). It bears strong spike-like spines laterally ( Fig. 19C ), dense, shorter spines medially, and similar dense but still shorter spines medially. The distal part of this field is entirely covered by spines whereas the more proximal part has large scutes or scales ( Fig. 19B ). The inner surface of the mandible is mostly covered with scutes, these grading towards the gnathal edge and ventral surface into scales with a few short denticles along their distal edge.

Gonibregmatidae : Eucratonyx

Epipharynx: The relatively broad and short labrum of Eucratonyx meinerti bears long, sharp, tapering spines ( Fig. 20A ) along its entire, medially embayed margin, those on the side-pieces directed inwards. The epipharynx is almost entirely covered by scales except for the proximo-lateral areas that are devoid of trichomes; when viewed from behind, the entire scale band approximates a Y-shaped form. The medial distal part of the epipharynx bears flattened scales ( Fig. 20B ). Towards the lateral and proximal edges of the scale field, the scales display a few small spines along their distal margins. The marginal spines (usually about four) are longer on the scales on the proximal part of the epipharynx ( Fig. 20B ), this scale field apparently extending towards the mouth opening. The branching scales grade into longer spines that form a dense field on the lateral distal part of the epipharynx. Only three sensilla coeloconica are present on the epipharynx ( Fig. 20C , sc), having an irregular scattering amidst the spinebearing scales on the most proximal median part of the epipharynx. Their structure and position indicate that they are the usual median clypeal group of sensilla coeloconica. The border between labral and clypeal parts (lp and cp, respectively, in Fig. 20A ) is largely indistinct. The extent to which the anterior branch of the fulcrum ( Fig. 20A , fu) laterally borders the epipharynx suggests that the transition from the labral to the clypeal part medially lies between the distal field of flattened scales and the proximal field of branching scales bearing sensilla; the lateral course of the transition remains unclear.

Hypopharynx: In Eucratonyx meinerti , the hypopharynx is moderately convex in lateral view ( Fig. 20D ). The entire dorsal and frontal surfaces are densely covered with bristles that branch along their lateral and distal margins into slender spines. In the lateral part of the bristle field (along the hypopharyngeal bar, hb) the marginal spines on the bristles are short but they become progressively longer and more needle-like medially. No sensilla have been observed along the lips or on the distal tip of the hypopharynx, although the density of spines may simply preclude their recognition. The openings of the hypopharyngeal glands ( Fig. 20F , ohg) are elongate slits at the base of the hypopharynx, oriented obliquely to the horizontal plane.

Mandible: The gnathal edge of the mandible in Eucratonyx meinerti is strongly curved ( Fig. 21D ) and bears spines aligned in one row that is differentiated along its length into two series: uniformly slender spines along the ventral half ( Fig. 21A–D , pl), and broader, bluntly pointed spines along the dorsal half, the latter being more strongly pigmented ( Fig. 21A, C, D , dl). Based on their degree of sclerotization, these two series are intepreted as two lamellae, including a dorsal sclerotized lamella. Much of the outer face of the mandible is covered by scales, the morphologies of these scales mirroring those on the epipharynx, i.e. flat, simple scales near the gnathal edge, grading into scales with a few short marginal spines more distally ( Fig. 21B ). The inner face of the mandible has a pervasive cover of scales that bear a fringe of small marginal spines, the spines becoming increasing long towards the gnathal edge. A field of long, slender spines is developed along the ventral margin of the mandible ( Fig. 21B , vm). The mandibular condyle is recurved and hook-like at its tip ( Fig. 21A , co).

Geophilidae

Epipharynx: The boundary between the labral and clypeal part of the epipharynx of Geophilidae is marked by a few consistent characters. The boundary describes a biconvex course, in most cases with a broad and moderately deep median embayment ( Fig. 23A, C ) but in the case of Geophilus carpophagus the boundary is nearly transverse ( Fig. 22A ). The transition from the labral to clypeal parts of the epipharynx consistently corresponds to an abrupt change in ornamentation, the labral part being essentially smooth and the clypeal part bearing scales that have a fringe of short spines along their distal margins ( Fig. 22A , inset; 22D, F, 23 D, H). The labral and clypeal parts have consistent relationships to the tentorium: the anterior branch of the fulcrum (fu in Figs 22 , 23 ) borders the lateral margin of the clypeal part and terminates at the corner of the labral part. Lastly, labral and clypeal parts are distinguished by the confinement of sensilla coeloconica to the clypeal part (as in Geophilomorpha generally). The border between the labral and clypeal parts as delimited by the above set of criteria typically corresponds as well to the most strongly defined furrow on the epipharynx ( Figs 22A , 23A, C, G ). Exceptionally the border is marked by an insignificant furrow ( Steneurytion antipodum : Fig. 22C ) and a stronger furrow parallels its course more proximally; in this case the more marked furrow on the epipharynx represents a groove that departs from regular bilateral symmetry and we identify it as an artefactual fold.

The labral part of the epipharynx is highly variable in extent. At one extreme, as in Zelanophilus provocator ( Fig. 22E ), it is represented only by smooth lateral fields below the labral side-pieces and a fringe of mid-piece teeth mesially, with the clypeal part representing most of the epipharynx. In this case, the border between labral and clypeal parts still is a concave notch, but the notch is mesially hidden by elongate spines of distal scales of the clypeal part that protrude over the border (a more marked furrow amidst the epipharynx is accordingly interpreted as an artefactual fold). At the other extreme, seen in Clinopodes flavidus ( Fig. 23A ) and Ribautia repanda ( Fig. 23C ), the labral part is expanded across both the mesial and the lateral areas below the mid-piece and side-pieces and is nearly as large in extent as the clypeal part. Mid-piece teeth and side-piece bristles correspond to prior morphological descriptions for these species; in geophilid species sampled here the mid-piece teeth are mostly differentiated from the side-piece bristles by being robust and dentiform ( Figs 22A , 23G ). In some instances, such as in Ribautia ( Fig. 23C ), the mid-piece is fringed by fimbriae that are barely distinguishable from those on the side-pieces. Side-piece bristles in several cases bear small spinules or denticles ( Fig. 23C, G , insets), and are most elaborately beset with dense spinules in Clinopodes flavidus ( Fig. 23A , inset) so as to confer a brush-like structure.

On the clypeal part of the epipharynx, scales are usually most pronounced in a median band of variable width. As noted above, these scales have a consistent morphology of bearing a fringe of several spines along their distal margin ( Figs 22D, F , 23D ). The scales in the median band are generally smaller than those more laterally ( Clinopodes : Fig. 23B ; Pachymerium ferrugineum : Fig. 23H ). On the lateral clypeal part of the epipharynx the fringe of spines along the distal margin of the scales gradually shortens and disappears more proximo-laterally and the scales are transformed into polygonal scutes. Sensilla coloeonica are confined to the proximo-median clypeal part, the sensilla being situated amidst the scales ( Figs 22B, F , 23B, E, F ). Only a few sensilla are present, either scattered over a small area ( Fig. 22B ) or aligned as a transverse band immediately in front of the mouth ( Fig. 23E ).

Zelanophilus ( Fig. 22E , obg) and Ribautia have a pair of ovate openings near the proximal edge of the epipharynx. As for similarly positioned structures in other geophilomorph families, these are interpreted as the openings of the median buccal glands.

Hypopharynx: In general, the geophilid hypopharynx projects as a relatively narrow, more or less tapering tongue-like process. Its frontal surface is variably convex ( Fig. 24B ), ranging to an extreme in the strongly convex Zelanophilus ( Fig. 25F ), in which the hypopharyngeal bars are distally connected to a semicircular arc extending along the length of the hypopharynx. In frontal view, the hypopharyngeal bars are usually confined to the proximal half of the hypopharynx ( Figs 24A, D, E , 25A, D ) and are variably oriented either parallel to the long-axis of the hypopharynx ( Clinopodes : Fig. 24A ; Geophilus : Fig. 24E ) or appear as triangular fields with an oblique orientation ( Ribautia : Fig. 25A ; Steneurytion : Fig. 25D ). Apart from the smooth surface of the hypopharyngeal bars and a variably present median plate on the backside in some species, most of the surface of the hypopharynx has a dense covering of branching scales that are patterned in parallel rows on both the frontal ( Fig. 25D ) and the back sides ( Fig. 25E ). Individual scales cannot be discerned on much of the spine field, the parallel rows being composed of uninterrupted series of slender, parallel spines of uniform length ( Fig. 25D , inset), but the origin of these rows from branching scales is seen in gradation to scales close to the hypopharyngeal bars in, for example, Clinopodes flavidus ( Fig. 24A ) and variably on the lips, where scales with a fringe of short spines may be present ( Geophilus : Fig. 24F ), although other taxa have long spines instead of scales on the lips ( Clinopodes : Fig. 24A ). In the spine field on the distal half of the hypopharynx, variably close to the lips, a few conical sensilla have been detected in some species ( Fig. 24D, F, G ). The sensilla are surrounded by a circular rim, the base of the sensillum being strongly demarked from the rim. The number of these sensilla in any species and even their presence in some geophilids for which we have not detected them are uncertain because they are readily concealed in the spine field. The longitudinal median incision on the frontal surface and distal tip of the hypopharynx continues in all Geophilidae along the backside of the hypopharynx. It either extends entirely to the base of the hypopharynx ( Fig. 24C, F , mi) or is interrupted before reaching the base by a wedge-shaped smooth field (‘median plate’) ( Fig. 25C, E : mp).

Mandible: The gnathal edge bears a single pectinate lamella. In the six species studied here, it is composed of 18–45 slender, mostly blunt-tipped or weakly pointed teeth that maintain an even width along the series. The pectinate lamella is gently curved and is aligned with the ventral margin of the mandible, the curve of the entire composite edge forming a tight arc ( Figs 26F , 27F ). The transition between the two regions is variably marked by deeper pigmentation of the pectinate lamella under light microscopy. In some species, the transition is additionally marked by an abrupt break in slope ( Clinopodes : Fig. 26D ) and a change from simple, blunt-tipped teeth on the pectinate lamella to tight groupings of more slender, pointed spines on the ventral margin ( Geophilus : Fig. 26E ) or an even more marked change to branching scales on the ventral margin ( Pachymerium : Fig. 26A ). In Ribautia ( Fig. 27C ) and particularly in Zelanophilus ( Fig. 27F, G ) the transition is clearly distinct but is less extreme. The slender spines on the ventral margin are clustered into small groupings in Ribautia ( Fig. 27D ). In Zelanophilus single elongate spines form a dense row, their bases extending more deeply than do the teeth of the pectinate lamella, as seen in an internal view ( Fig. 27F, G ). The outer surface of the mandible bears strong scales with a fringe of short spines along their distal margin in all geophilids; the scales are at least as strongly developed on the ventral surface as well. The mandibular condyle is highly variable, developed as a prominent hook in some taxa ( Pachymerium : Fig. 26B , co; Zelanophilus : Fig. 27E ), an unhooked process ( Ribautia : Fig. 27A ), or indistinctly swollen ( Clinopodes : Fig. 26D ). The lamina condylifera is not delimited by a suture. The inner surface of the mandible is strongly ornamented, generally with scales on the proximal part that grade into a field of short, dense spines towards the pectinate lamella and the fringe of spines on the ventral edge ( Fig. 27B, F ).

Linotaeniidae

In contrast to a lack of data for most other geophilomorphs in the literature, the epipharynx of Strigamia has been illustrated by line drawings in several works, including Latzel (1880: S. crassipes ), Crabill (1954: S. acuminata and S. fulva ), and Pereira (2009: Strigamia hoffmani ). The arrangements of sensilla on the clypeal part of the epipharynx have been depicted as variable between species ( Crabill, 1954: figs 1, 4).

Epipharynx: The labral mid-piece and side-pieces of Strigamia maritima (corresponding to ‘lp’ and ‘lsp’, respectively, on the epipharynx; Fig. 28A ) are sharply delineated. The mid-piece has a lenticular outline, its anterior half bearing a fringe of robust, pointed spines, set off from the smooth posterior half by a shallow transverse furrow. The side-piece ( Fig. 28A , lsp) bears a tooth at its anteromedial apex. The clypeal part of the epipharynx has a bilobate anterior margin and nearly transverse proximal margin as in Geophilidae , with a strong, rounded median embayment where the labral mid-piece inserts. The surface of the clypeal part has scales in a wide median band, these scales bearing a fringe of several short, pointed spines along their distal margins; the lateral parts, in contrast, are more or less smooth, with a weak texture of polygonal scutes discernable. A transverse band of three sensilla coeloconica ( Fig. 28A , inset) spans the medial part a short distance in front of the proximal margin.

Hypopharynx: The outline of the hypopharynx of Strigamia maritima in frontal view is subpentagonal ( Fig. 28B ), although it is relatively strongly arched across its width ( Fig. 28C ) and its distal tip projects as a pronounced tongue in lateral aspect. The lateral flanks and the triangular proximal depression from which the frontal groove arises are smooth and unornamented. The lips of the hypopharynx bear simple spines that extend further laterally closer to the distal tip, where they display a patterning into parallel bands; the spine field narrows again on the backside of the hypopharynx ( Fig. 28C ). The most medial part of the lips bears narrower and shorter spines than elsewhere, these spines being grouped in rows as the fringes of scales. Near the transition between the more robust spines on the lips and the shorter spines grouped as scale fringes are a few conical sensilla ( Fig. 28D ), two such sensilla being detected on each side of the hypopharynx. Its backside displays a marked median incision and paired elongate openings of the hypopharyngeal glands proximo-laterally ( Fig. 28C ).

Mandibles: The gnathal edge bears a single pectinate lamella composed of c. 21 teeth that are tapered near their tips and terminate in blunt points. The proximal pair of teeth is more widely separated than are the others ( Fig. 30F ). The outer surface of the mandible has a subdued ornament of scutes; more strongly defined, elongate, scale-like scutes are present along the ventral margin of the gnathal lobe. A condyle is indistinct.

Figures

Figure 1. Hydroschendyla submarina, 3D reconstructions of the head (antennae cut off at their base and forcipules removed) based on histological sections (volume rendering), showing the position of the regions of interest of the present study. A, complete head reconstruction in oblique-frontal view; rectangle indicates the position where heads were sliced into two halves to examine epi- and hypopharynx by SEM; B, anterior half of the head, oblique view from behind on epipharynx; C, posterior half of the head, same view as in A but with the anterior half removed to show the hypopharynx and mandibular gnathal lobes. Abbreviations: an, antenna; br, brain; ep, epipharynx; hy, hypopharynx; md, mandible; mo, mouth; mx I, first maxilla; mx II, second maxilla.

Figure 2. Light micrographs of peristomatic structures of Geophilomorpha. A-D, Dicellophilus carniolensis. A, overview of epipharynx; B, left fulcrum and bucca (ventral view); C, overview of hypopharynx (frontal view); D, apex of hypopharynx (ventral view), showing sclerotized bars between lateral and median lobes. E, Plesioschendyla confossa, overview of epipharynx. F, Hydroschendyla submarina, overview of epipharynx. G, Himantarium gabrielis, ventral view on anterior half of head capsule after dissection of mouthparts. H, Gonibregmatus anguinus, ventral view on anterior half of head capsule after dissection of mouthparts. Abbreviations: bc, bucca; cl, clypeal part of clypeolabrum; cp, clypeal part of epipharynx; eb, epipharyngeal bar of fulcrum; ep, epipharynx; fu, fulcrum; hb, hypopharyngeal bar of fulcrum; hy, hypopharynx; lp, labral part of epipharynx; lsp, labral side-piece or side parts; no, notch between lateral and mesial lobes of hypopharynx; ph, pharynx; pl, cephalic pleurite; sf, sclerite of hypopharyngeal furrow; st, stilus; tb, transverse bar of fulcrum.

Figure 3. Epipharynx of Mecistocephalidae. A, Dicellophilus carniolensis. B, Tygarrup diversidens. C, Arrup kyushuensis. Ellipses refer to sensilla clusters (for higher magnifications see Fig. 4). Dashed line in B marks the indistinct border between labral and clypeal parts of the epipharynx. Abbreviations: cp, clypeal part of epipharynx; eb, epipharyngeal bar of fulcrum; lmp, labral mid-piece; lp, labral part of epipharynx; tp, tooth plate.

Figure 4. Epipharynx of Mecistocephalidae. A–B, Dicellophilus carniolensis. A, labral mid-piece tooth (tp) and labral bristle bands; B, median cluster of seven sensilla amidst bristle bands. C, Arrup kyushuensis, sensilla on clypeal part in (3+1+2) arrangement (counted from anatomically left to right). D, Mecistocephalus tahitiensis, sensilla on clypeal part in (2+1+3) arrangement (counted from left to right). E–F, Tygarrup diversidens. E, sensilla on clypeal part in (3+1+2) arrangement (counted from left to right); F, higher magnification of left sensilla cluster.

Figure 5. Peristomatic structures of Mecistocephalus sp. from Lord Howe Island. A, epipharynx, ellipse refers to transverse cluster of sensilla (inset); B, hypopharynx, frontal view; C, gnathal edge of right mandible, external face (anterior to right, dorsal to top); D, gnathal edge of left mandible, mesial view on internal face (dorsal to top). Abbreviations: cp, clypeal part of epipharynx; dsl, dorsal sclerotized lamella of mandibular gnathal edge; fr, furrow between lateral and mesial lobes of hypopharynx; lp, labral part of epipharynx; mo, mouth; no, notch between lateral and mesial lobes of hypopharynx; tp, tooth plate.

Figure 6. Hypopharynx of Mecistocephalidae. A, Tygarrup diversidens, frontal view (dorsal to top). B, Arrup kyushuensis, ventral view (the frontal surface of the anatomically right half broken off); arrow points to cluster of conical sensilla. C–E, Dicellophilus carniolensis. C, oblique latero-frontal view (anterior to left); D, spine clusters on distal tip, and E, detail of conical sensilla at edge of spine fields. Abbreviations: fr, furrow between lateral and mesial lobes of hypopharynx; no, notch between lateral and mesial lobes of hypopharynx; ph, pharynx.

Figure 7. Mandibles of Mecistocephalidae. A, Tygarrup diversidens, left gnathal lobe in dorsal view (anterior to top). B, Arrup kyushuensis, left gnathal lobe in dorso-lateral view (anterior to left). C–E, Dicellophilus carniolensis. C, right gnathal lobe in frontal view (dorsal to top); D, right gnathal edge (frontal view) at higher magnification; E, mesial view on right gnathal edge (dorsal to top). Abbreviations: co, condyle; tt, translucent tooth.

Figure 8. Series of transverse histological sections of the head, from anterior to posterior. A–C, Dicellophilus carniolensis. D–G, Hydroschendyla submarina. Abbreviations: dhg, duct of hypopharyngeal gland; eb, epipharyngeal bar of fulcrum; fp, frontal process of epipharyngeal bar; hb, hypopharyngeal bar of fulcrum; hy, hypopharynx; lsp, labral side-piece or side parts; m20, mandibular muscle 20 (fide Manton, 1965); mb, mesial bar of fulcrum; md, mandible; ph, pharynx; pp, posterior process of fulcrum (= anterior tentorial apodeme); sf, sclerite of hypopharyngeal furrow; st, stilus of bucca; t1, tentorial muscle 1; t2, tentorial muscle 2; tb, transverse bar of fulcrum.

Figure 9. Epipharynx of Himantariidae. A–C, Haplophilus subterraneus. A, overview of epipharynx; B, lateral clypeal part, arrows point to spear-shaped sensilla; C, median clypeal part, arrows point to sensilla coeloconica. D, E, Bothriogaster signata. D, overview of epipharynx; E, sensilla coeloconica on median clypeal part. F, G, Himantarium gabrielis. F, three sensilla coeloconica amidst field of spines on median clypeal part; G, spear-shaped sensilla on lateral clypeal part. Abbreviations: cp, clypeal part of epipharynx; fu, fulcrum; lp, labral part of epipharynx; obg, opening of median buccal gland; ph, pharynx.

Figure 10. Hypopharynx of Himantariidae. A, Bothriogaster signata, lateral view (anterior is right). B–D, Himantarium gabrielis. B, dorsal view; C, ventral view; arrow points to conical sensillum shown in D at higher magnification. E, F, Haplophilus subterraneus. E, oblique ventro-lateral view. F, cluster of sensilla on distal tip, its position indicated in E. Abbreviations: hb, hypopharyngeal bar of fulcrum; mo, mouth; ohg, opening of hypopharyngeal gland; ph, pharynx.

Figure 11. Mandibles of Himantariidae. A, Haplophilus subterraneus, right gnathal lobe in frontal view (dorsal to top). B–D, Himantarium gabrielis. B, right gnathal lobe in frontal view (dorsal to top); C, right gnathal edge in ventral view; D, the most proximal lamellae of the right gnathal lobe in mesial view. E, Bothriogaster signata, right gnathal lobe in mesial view (dorsal to right). Abbreviations: co, condyle; dsl, dorsal sclerotized lamella; lc, lamina condylifera.

Figure 12. Epipharynx of Oryidae. A, Orya almohadensis. Insets depict sensilla coeloconica of a broad median cluster (top inset) and spear-shaped sensilla of paired lateral clusters on the clypeal part (bottom inset). B, Notiphilides maximiliani, most proximal median area of the clypeal part (distal to top), showing mesially confluent clusters of spear-shaped sensilla. C, Orphnaeus brevilabiatus, proximal area of clypeal part (left side, distal to top), showing sensilla coeloconica mesially and spear-shaped sensilla laterally. Abbreviations: cp, clypeal part of epipharynx; fu, fulcrum; lp, labral part of epipharynx.

Figure 13. Hypopharynx of Oryidae. A–C, Orya almohadensis. A, overview of hypopharynx (frontal view, dorsal to top); B, detail of right proximo-lateral area, showing cluster of spear-shaped sensilla; C, ventral view (anterior to top), showing dense aggregation of sensilla on backside of hypopharynx. D–E, Orphnaeus brevilabiatus. D, ventral view on backside of hypopharynx (anterior to top); E, sensilla on hypopharyngeal backside in higher magnification. Abbreviations: hb, hypopharyngeal bar of fulcrum; ohg, opening of hypopharyngeal gland; ph, pharynx.

Figure 14. Mandibles of Oryidae. A, Notiphilides maximiliani, oblique fronto-mesial view on right gnathal lobe (dorsal to top). B–D, Orya almohadensis, left gnathal lobe. B, fronto-dorsal view (external face); C, mesial view (internal face, dorsal to top); D, ventro-mesial view. Abbreviations: co, condyle; pl, pectinate lamella; vm, ventral margin of gnathal lobe.

Figure 15. Epipharynx of Schendylidae and Ballophilidae. A–B, Plesioschendyla confossa. A, overview; B, detail of left clypeal part, showing sensilla coeloconica medially and spear-shaped sensilla laterally. C, Ballophilus rouxi, overview. D–F, Pectiniunguis argentinensis. D, median clypeal part, showing sensilla coeloconica (arrows) amidst scale-like spines; E, same, showing sensillum coeloconicum in higher magnification; F, lateral clypeal part (right side), showing cluster of spear-shaped sensilla next to median field of scale-like spines. G, H, Hydroschendyla submarina. G, overview; H, detail of left clypeal part, showing lateral cluster of spear-shaped sensilla next to median field of scale-like spines. Abbreviations: cp, clypeal part of epipharynx; lp, labral part of epipharynx; sc, sensillum coeloconicum; sp, spear-shaped sensillum.

Figure 16. Hypopharynx of Schendylidae and Ballophilidae. A, Plesioschendyla confossa, frontal view (dorsal to top). B–D, Ballophilus rouxi. B, frontal view (dorsal to top); C, detail of right proximal area immediately in front of mouth, showing cluster of spear-shaped sensilla. D, ventral view on backside of hypopharnyx (anterior to top). E, F, Hydroschendyla submarina. E, ventral view on hypopharyngeal tip and backside; F, frontal view on most proximal area in front of the mouth (dorsal to top), showing spear-shaped sensilla at the base of the median lips. Abbreviations: hb, hypopharyngeal bar; mi, median incision on hypopharyngeal backside; mo, mouth; ohg, opening of hypopharyngeal gland; ph, pharynx; sp, spear-shaped sensillum.

Figure 17. Mandibles of Schendylidae and Ballophilidae. A, B, Ballophilus rouxi. A, fronto-lateral view on external face of right gnathal lobe (dorsal to top); B, mesial view on internal face of right gnathal lobe (dorsal to top). C, Hydroschendyla submarina, dorso-lateral view on right gnathal lobe (anterior to right); the dorsal sclerotized lamella is resolved into three groups of teeth (arrows). D, E, Plesioschendyla confossa. D, dorso-lateral view on right gnathal lobe (anterior to top); E, mesial view on internal face of right gnathal edge (dorsal to top). F, G, Pectiniunguis argentinensis. F, dorsal view on right gnathal lobe (anterior to right), showing the dorsal sclerotized lamella resolved into three groups of teeth; G, mesial view on internal face of right gnathal edge (dorsal to top). Abbreviations: co, condyle; dl, dorsal sclerotized lamella; lc, lamina condylifera.

Figure 18. Peristomatic structures of Gonibregmatus anguinus. A, B, epipharynx. A, posterior view on clypeolabrum (median labral area broken off), depicting the strong lateral compression of the epipharynx; inset shows a lateral section of the row of denticles on the labral margin; B, proximal area of clypeal part of epipharynx, highlighted by box in A, showing spear-shaped sensilla. C–E, hypopharynx. C, frontal view (dorsal to top); D, ventral view on backside, showing median complete incision; E, frontal view on distal tip, inset showing conical sensilla on lips. Abbreviations: cl, clypeal part of clypeolabrum; ep, epipharynx; fu, fulcrum; lp, labral part of epipharynx; mi, median incision on hypopharyngeal backside; ph, pharynx.

Figure 19. Mandible of Gonibregmatus anguinus. A, lateral view on external face of left gnathal lobe (anterior to left, dorsal to top); B, ventral view on left gnathal lobe (anterior to top), showing its sculptured internal face; C, detail of spine field on ventral margin of left gnathal lobe. Abbreviations: pl, pectinate lamella; vm, ventral margin of mandibular gnathal lobe.

Figure 20. Peristomatic structures of Eucratonyx meinerti. A–C, epipharynx. A, overview; B, distal median area below spines of labral margin; C, median clypeal part, showing bottle-shaped sensilla coeloconica amidst field of branching scales. D–F, hypopharynx, left half. D, lateral view (anterior to top); E, frontal view (dorsal to top); F, ventral view (anterior to top); inset in E shows detail of bristles along hypopharyngeal bar. Abbreviations: cp, clypeal part of epipharynx; fu, fulcrum; hb, hypopharyngeal bar of fulcrum; lp, labral part of epipharynx; ohg, opening of hypopharyngeal gland; sc, sensillum coeloconicum.

Figure 21. Mandible of Eucratonyx meinerti. A, lateral view on external face of left gnathal lobe (anterior to left, dorsal to top); arrowhead indicates the border between the lightly and strongly sclerotized lamellae; B, ventral view on right gnathal lobe (anterior to top), showing the transition of the pectinate lamella into dense spine field on ventral margin; C, dorso-mesial view on gnathal edge of left mandible; arrowhead indicates the border between the two lamellae; D, mesial view on internal face of left gnathal lobe (dorsal to left). Abbreviations: co, condyle; dsl, dorsal sclerotized lamella; pl, pectinate lamella; vm, ventral margin of mandibular gnathal lobe.

Figure 22. Epipharynx of Geophilidae. A, B, Geophilus carpophagus. A, overview; inset shows branching scales on distal clypeal part at higher magnification; B, proximal median area of clypeal part (indicated by box in A), showing bottle-shaped sensilla coeloconica (arrows) amidst field of scale-like spines. C, D, Steneurytion antipodum. C, overview; D, proximal median area of clypeal part (indicated by box in C); arrow points to bottle-shaped sensillum coeloconicum. E, F, Zelanophilus provocator. E, overview; inset shows branching scales on distal clypeal part in higher magnification; F, median area of clypeal part (indicated by box in E), showing bottle-shaped sensilla coeloconica (arrows). Abbreviations: cp, clypeal part of epipharynx; fu, fulcrum; lp, labral part of epipharynx; obg, opening of median buccal gland; ph, pharynx.

Figure 23. Epipharynx of Geophilidae. A, B, Clinopodes flavidus. A, overview; inset shows the tips of plumose spines on labral margin; B, detail of proximo-medial clypeal part, showing row of bottle-shaped sensilla coeloconica (inset). C–F, Ribautia repanda. C, overview; inset shows the tips of spines on labral margin; D, detail of lateral clypeal part (indicated by box in C), showing scale-like spines; E, detail of proximo-median clypeal part, showing row of sensilla coeloconica; F, sensillum coeloconicum on proximo-median clypeal part at higher magnification. G, H, Pachymerium ferrugineum. G, overview; inset shows spines on labral margin in higher magnification; H, detail of border between labral and clypeal parts (indicated by box in G). Abbreviations: cp, clypeal part of epipharynx; fu, fulcrum; lp, labral part of epipharynx.

Figure 24. Hypopharynx of Geophilidae. A–C, Clinopodes flavidus. A, dorsal view on frontal surface (anterior to bottom); B, lateral view (anterior to left); C, ventral view on backside (anterior to top). D, Pachymerium ferrugineum, dorsal view on frontal surface (anterior to bottom); inset shows conical sensillum amidst distal spine field in higher magnification. E–G, Geophilus carpophagus. E, dorsal view on frontal surface (anterior to bottom); F, frontal view on hypopharyngeal apex (dorsal to top); G, two conical sensilla amidst spine field on median lips (position indicated by box in F). Abbreviations: hb, hypopharyngeal bar of fulcrum; mi, median incision on hypopharyngeal backside; ohg, opening of hypopharyngeal gland; ph, pharynx.

Figure 25. Hypopharynx of Geophilidae. A–C, Ribautia repanda. A, dorsal view on frontal surface (anterior to bottom); B, frontal view on hypopharyngeal tip (dorsal to top); C, ventral view on backside (anterior to top). D, E, Steneurytion antipodum. D, dorsal view on frontal surface (anterior to bottom); E, fronto-lateral view on backside (dorsal to top, anterior to left). F, G, Zelanophilus provocator. F, fronto-lateral view on backside (dorsal to top, anterior to right); G, ventro-lateral view on backside (anterior to top). Abbreviations: hb, hypopharyngeal bar of fulcrum; mi, median incision on hypopharyngeal backside; mo, mouth; mp, median plate on hypopharyngeal backside; ph, pharynx.

Figure 26. Mandibles of Geophilidae. A, B, Pachymerium ferrugineum. A, mesial view on gnathal edge of left mandible (anterior to right, dorsal to top); B, lateral view on gnathal lobe of left mandible (anterior to left, dorsal to top). C, E, Geophilus carpophagus. C, mesial view on gnathal edge of left mandible (anterior to right, dorsal to top); E, transition of pectinate lamella into branching spines on ventral margin. D, Clinopodes flavidus, ventral view on gnathal lobe of left mandible (anterior to top). F, Steneurytion antipodum, mesial view on gnathal edge of left mandible (anterior to right, dorsal to top). Abbreviations: co, condyle; pl, pectinate lamella; vm, ventral margin of gnathal lobe.

Figure 27. Mandibles of Geophilidae. A–D, Ribautia repanda. A, lateral view on external surface of right mandible (dorsal is top, anterior is right); B, mesial view on internal surface of right gnathal lobe (dorsal to top, anterior to left); C, external view on ventral margin of right gnathal lobe (anterior to top); D, detail of C, showing branching spines on ventral margin of right gnathal lobe. E–G, Zelanophilus provocator. E, dorsal view on right gnathal lobe (anterior to left); F, mesial view on internal surface of right gnathal lobe (dorsal to top, anterior to left); G, internal view on ventral margin of right gnathal lobe (anterior to left, dorsal to top). Abbreviations: co, condyle; pl, pectinate lamella; vm, ventral margin of gnathal lobe.

Figure 28. Peristomatic structures of Strigamia maritima. A, epipharynx (anterior to top), inset showing two of three sensilla coeloconica on proximo-median clypeal part. B, hypopharynx, frontal view (dorsal to top). C, backside of hypopharynx, ventral view (anterior to top). D, conical sensillum amidst branching scales on right frontal side of hypopharynx (position indicated in B, cs). Abbreviations: cp, clypeal part of epipharynx; cs, conical sensillum; fu, fulcrum; hb, hypopharyngeal bar of fulcrum; lp, labral part of epipharynx; lsp, labral side-piece; mi, median incision on hypopharyngeal backside; mo, mouth; ohg, opening of hypopharyngeal gland.

Figure 30. Mandibles of Dignathodontidae and Linotaeniidae. A–C, Henia vesuviana. A, fronto-mesial view on external surface of left gnathal lobe (dorsal to left); B, lateral view on external surface of left gnathal lobe (dorsal to top, anterior to left); C, mesial view on internal surface of pectinate lamella of left gnathal lobe (dorsal to left). D, E, Dignathodon microcephalus. D, ventro-mesial view on internal surface of left gnathal lobe (dorsal to top); E, lateral view on external surface of left gnathal lobe (dorsal to top). F, Strigamia maritima, mesial view on internal surface of right gnathal edge (anterior to top, dorsal to right). Abbreviations: co, condyle; pl, pectinate lamella; vm, ventral margin of gnathal lobe.