Acrotelsella hethicola, Smith & Mitchell, 2024

Smith, Graeme B. & Mitchell, Andrew, 2024, On some silverfish taxa from the Cape York region of northern Australia (Zygentoma: Lepismatidae: Ctenolepismatinae), Records of the Australian Museum (Rec. Aust. Mus.) 76 (1), pp. 1-68 : 44-51

Acrotelsella hethicola sp. nov.

urn:lsid:zoobank.org:act:23D6DFF4-7B76-48D9-90D5-27BDFDB4DBAC

Figs 128–149

Holotype ♂ (HW 1.08) QUEENSLAND: Jardine River NP, track to Jardine River South campsite 11.2167°S 142.3569°E 72m asl, 22.vii.2013, Graeme Smith, Eucalypt leaf litter,

QMT259417 (on two slides). Locality shown on the map in Figure 128 .

Diagnosis. This species, while only known from a single male, is genetically, morphologically and geographically close to Acrotelsella septentrionalis sp. nov. but is easily distinguishable from it by the smaller number of papillae on the labial palps (five versus 7–10), by the preponderance of circular sensilla rather than basiconic sensilla on the distal articles of the antennae and the distal article of the labial palp, by the concave posterior margins of all thoracic sterna, and by the rounded internal processes of coxites IX of the males.

Description

Appearance: Small to medium sized silverfish, somewhat stocky in form, thorax wider than the abdomen. Scale pattern when live see Figure 129 , antennae evenly brown, terminal filaments annulated; distinct band of dark scales on back of head; upper surface of legs dark. The single specimen known was about to moult so it was often possible to see the sclerites and macrochaetae of the newly forming cuticle beneath the old, which sometimes made it difficult to interpret when drawing the illustrations.

Body length: H+B up to 7.1 mm, HW 1.08 mm; thorax: length 2.4 mm or 0.33 H+B; width 1.88 mm with the mesonotum being slightly wider than the pronotum and not much wider than the metanotum. Antennae incomplete, maximum preserved length 5.5 mm or>0.77 H+B; terminal filaments all broken, maximum length of terminal filaments 2.5 mm or>0.35 H+B.

Pigmentation: Cuticle overall moderately dark when placed into alcohol. The intensity of darkness makes it a little difficult to observe macrochaetae insertions in some places. Flagellum of antennae without banding, moderate brown pigment evenly distributed; pedicel and scape not particularly strongly pigmented. Frons without darker regions, labrum and clypeus without pigment, mandibles and maxillae without pigment among bushes of macrochaetae, maxillary and labial palps with brown pigment, the ultimate and penultimate articles of the maxillary palp pigmented overall but a little darker distally, other articles with some pigment distally. Ultimate article of labial palp with pigment around margins, other articles with very little pigment. Nota and thoracic sterna without obvious pigment. Some pigment on “shoulder” of the coxa of PI but not along the outer margin nor on PII or PIII. Trochanter without distinct pigment. Femora fairly evenly pigmented or sclerotised, tending to darker at the posterior bulge and the anterior distal corners. Tibia of all legs a little darker distally. All tarsal articles without much pigment. Abdominal segments with little pigment but coxites IX have pigment around the insertion of the styli. Cerci and median filament annulated in photo when live but any annulation difficult to see in preserved material. Abdominal styli light basally with a little darker pigment distally.

Macrochaetae: Variable, strongly pectinate ( Figs 130–132 ) elongate, tapered or carrot-shaped and strongly pectinate or more subtly pectinate, curved and tapered dark brown to hyaline.

Scales: Variable, some with numerous sub-parallel ribs that do not surpass the margin of the scale, others with ribs that appear to merge towards the mid-line ( Fig. 132 ) some scales with ribs more widely spaced others closer together. Dorsal scales are brown to hyaline, those on ventral surface brown or hyaline. Scales found on frons and clypeus, on pedicel and scape, on second and third articles of maxillary palp, the submentum, all nota, all thoracic sterna, legs (except for trochanter and distal three articles of tarsi), all urotergites and urosternites, styli, medial filament and cerci. Scales of palps, styli, terminal filaments of variable size, form not well understood due to orientation in slide material.

Head: ( Fig. 134 ) wider than long with 1+1 not very dense bushes of macrochaetae aligned in subparallel rows on the antero-lateral corners, with a distinct gap in chaetotaxy between these two bushes. Eyes dark brown in alcohol preserved material. There is a small gap behind each bush in the row of macrochaetae along the margin which extends inwards a little near a large but isolated peri-antennal group and its long thin trichobothrium-like seta; the marginal row continues back and up over the eyes about one to two macrochaetae wide. Clypeus with 1+1 very dense bushes of strongly pectinate macrochaetae as well as a few curved setae laterally, with only a single cilium on the face between the bushes. Labrum also with 1+1 bushes but these are less dense, as well as many simple setae and cilia scattered over the face and a single macrochaeta medially between the bushes. — Antennae fairly long, scape ( Fig. 135 ) not long with scales over much of its surface and a preapical ring of setae; pedicel with sacles and preapical ring of simple setae and cilia and setae scattered over internal face; first annulus/ interval of flagellum with an incomplete subapical ring of simple setae; next four annuli each with a single ring of simple setae and a short trichobothrium; intervals six and seven similar but with additional long cilia; articles eight and nine with two rings, the basal only with setae and cilia, the distal similar but with a long trichobothrium; article ten with three rings the basal two of setae only or perhaps also a trichobothrium, the distal as in the previous interval. Most distal surviving intervals ( Fig. 136 ) consisting of two very similar chains, the basal of four annuli, the distal of five; circular sensilla can be seen in the basal three annuli of the basal chain and the basal two or three annuli of the distal chain, most annuli with a sub-basal ring of setae and sometimes a subdistal ring of cilia; basiconic sensilla not observed. — Mandibles typical for Acrotelsella with well-developed molar and incisor areas; a group of about ten short apically bifurcated but simple setae distally adjacent to the pectinate molar area and large bushes of pectinate macrochaetae externally as well as scattered simple setae. — Maxilla ( Fig. 137 ) with two thick minutely apically bifurcated and very subtly pectinate macrochaetae as well as two smaller setae externally proximal to the palp, the lacinia with three strong teeth, one set further back than the other two, followed by about five or six lamellate processes and a row of 5–6 short simple setae, galea longer than lacinia with about 3–4 strong smooth simple or apically bifurcate setae externally in its basal half and several cilia distally; maxillary palp not very elongate, apical article 5.4 times longer than wide and 1.13 times as long as the penultimate article which is the longest article, the ultimate article with a circular sensillum subapically, last two articles of palp with fine setae only, third article with some slightly stronger setae subapically, second and third articles also with scales, although these can be hard to find on the third article. — Labium ( Fig. 138 ) short and broad, postmentum with transverse row of simple and apically truncate smooth setae, prementum with transverse and oblique rows of strong apically truncate setae, apically with long curved setulae; labial palp short, apical article only slightly not expanded medially, about as long as wide (L/ W 1.07) with row of five papillae of compact type arranged in a single curved row, with a single circular sensillum on the outer margin, face covered with numerous fine setae as well as longer fine setae.

Thorax: Pronotum ( Fig. 139 ) with dense setal collar of both longer and shorter pectinate macrochaetae, about three macrochaetae wide, without slight medial gap; lateral margins with strong shorter and longer curved slightly pectinate macrochaetae as well as a few cilia, with 8–9 combs of 1–3 macrochaetae along each margin. Two open trichobothrial areas; the posterior trichobothrial area located about 0.70 of the distance along the margin and is associated with the last comb (N), this comb composed of three macrochaetae with the short trichobothrium at the mediad end and a cilium at the laterad end, the anterior trichobothrial area is forward of the midpoint (0.36) and associated with comb N-3, the comb composed of only a single macrochaeta with the trichobothrium between the macrochaeta and the margin and a cilium laterad of the trichobothrium; all combs associated with a few setulae, never very numerous. Posterior margin of all nota with 1+1 combs of 5–7 macrochaetae insertions associated with a couple of setulae between the comb and the margin and a cilium at each end, the macrochaetae are all lost but the most laterad insertion is almost certainly occupied by a long thin trichobothrium-like macrochaeta based on the shape of the insertion hole; these combs not particularly widely spaced (gap between them 45% of total width of pronotum). — Mesonotum ( Fig. 140 ) with lateral chaetotaxy similar to pronotum although fewer marginal setae and nine combs of 1–3 macrochaetae, the anterior trichobothrial area located 0.52 along the lateral margin, associated with comb N-2 composed of one macrochaeta with the trichobothrium located between the macrochaeta and the margin, with a few setulae posterior to the comb and a cilium between the trichobothrium and the margin. Posterior trichobothrial area slightly more posterior than that on the pronotum (0.79) the trichobothrium located mediad to the comb usually of three macrochaetae and with 1–4 setulae or stronger setae posterior to the comb.— Metanotum ( Fig. 141 ) similar to mesonotum with eight combs of 1–3 macrochaetae, the anterior trichobothrial area associated with comb N-1 of one macrochaeta about 0.67 the distance along the margin, the trichobothrium located between the margin and the macrochaeta, the posterior trichobothrial area associated with the most posterior comb (0.83 along the margin) of three macrochaetae.

Presternum narrow with transverse row of short pectinate setae ( Fig. 142 ) without scales or cilia between the row of setae and the prothoracic sternum. — Prothoracic sternum ( Fig. 142 ) approaching trapezoidal with concave posterior margin (however the newly developing cuticle of the next stadium is visible beneath the surface and it does not show any concave region between the most posterior combs), a little wider than long (L/ W 0.93) antero-lateral corners with about ten finely pectinate tapered marginal setae, posterior ⅘ of lateral margins with fringe of setae as well as 9–10 short combs on each side each composed of 1–8 pectinate macrochaetae. — Mesosternum ( Fig. 143 ) only a little larger than prosternum (1.15 times as long) about as long as wide at its base (L/ W 1.07) and of similar shape, anterolateral corners glabrous, posterior third of margins with many long thin setae and 3–4 combs on each side distally, teach composed of 4–11 pectinate macrochaetae in a single line; all combs with a few setulae behind them, larger smooth, tapered macrochaetae sometimes on the margin. — Metasternum ( Fig. 144 ) of similar length to prosternum except wider (L/ W 0.87) apically also with small concave margin, with marginal setae and occasional cilia along distal 1 / 4 of lateral margins and 4+4 combs of 3–11 pectinate macrochaetae although the close proximity of the more posterior combs suggest these may merge in some individuals to give a 3+3 or 3+4 arrangement as seen on the mesosternum.

Legs quite long, difficult to measure in alcohol because of alignment of specimen, tibia L/W ratio of PII 4.1. PI ( Fig. 142 ) with a comb of 4–5 pectinate macrochaetae laterally on the distal margin of the precoxa. Coxa with scales and a group of about 12 macrochaetae on the anterolateral corners usually arranged in two irregular rows, followed by a field of strong pectinate macrochaetae along the external margin about 3–4 macrochaetae wide; inner margin with 5–6 lightly pectinate tapering macrochaetae and several setae of varying thickness distally over the articulation. Trochanter with setae, setulae and cilia. Femur posteriorly with several long carrot-shaped pectinate macrochaetae as well as some thinner pectinate macrochaetae, some cilia and small setae, dorsal margin with at least three strong curved pectinate macrochaetae over the articulation. Tibia of PI with about eight stout, pectinate mostly carrot-shaped macrochaetae along the ventral and distal margins as well as several smooth setae, dorsal margin with two short curved mildly pectinate macrochaetae spaced along the margin and a few smooth setae and long scales subdistally, with usual tibial spur bearing a few setae. Tarsi with four articles, the basal article of PI about half the total length of the tarsus, its join with the next article not particularly oblique, the surface of all tarsal articles with numerous simple setae, those ventral near the distal end of the basal three articles more robust and with more rounded tips, especially on the two basal articles. Pretarsus with two long curved lateral claws and a shorter curved medial empodial claw. PII ( Fig. 143 ) and PIII ( Fig. 144 ) similar to PI except the antero-lateral groups of macrochaetae on the coxa absent; legs progressively longer from PI to PIII and the relative length of the basal tarsal article is progressively longer being about 0.6 of the total length on PIII.

Abdomen: Urotergite I with 1+1 lateral combs of five macrochaetae each associated with a cilium at least at the external end and 2–4 small marginal setae and 1–2 setulae between the comb and the margin, urotergites II–VII ( Fig. 145 ) with 3+3 combs of macrochaetae as in Table 10, the lateral combs with two cilia as well as 2–4 small marginal setae and 1–7 setulae, the sublateral combs with a cilium at the mediad end as well as 2–3 small marginal setae and 2–4 setulae, the submedial combs with a cilium at the laterad end as well as 2–3 small marginal setae and 2–4 setulae; urotergite VIII with 2+2 combs (lacking the sublateral), also with a cilium at each end of both combs as well as 1–4 marginal setae and 5–6 setulae, urotergite IX glabrous. — Urotergite X ( Fig. 146 ) almost equilateral triangle (72°), wider at base than long (L/ W 0.64) with many long fine pectinate tapered setae and setulae along entire margin, and 4+4 combs of 1–5 macrochaetae per comb but very few setulae posterior to each comb, and most combs with a cilium at the mediad end.

Urosternite I and II glabrous, urosternites III–VII with 1+1 lateral combs of 17–20 pectinate macrochaetae ( Fig. 147 ) each with several small marginal setae and several setulae between the comb and the margin as well as a cilium at the laterad end of every comb. The distance between the lateral combs 2.1–3.2 times the average width of these combs, the ratio being largest on urosternite III and decreasing posteriorly.

Genital region of ♂ as in Figure 148 . Two pairs of styli, those on IX long and slender with robust setae apically and along the length of the stylus, styli of VIII similar and not much smaller. Urosternite VIII entire with long combs of 16–17 macrochaetae and about half this number of marginal setae and a few setulae in between the two, the margin between the styli slightly concave. Coxites IX in ♂ separated with internal process not very broad and short being only 1.1–1.2 times longer than wide at its base and 3.4 times longer than the short pointed external process, the inner processes not quite reaching to half the length of the stylus; outer process with finely pectinate setae along the outer margin, inner process with setae and finely pectinate tapered macrochaetae along both margins, as well as three submarginal combs of 1–5 macrochaetae along the inner margin, and a macrochaeta inserted mediad of the base of the stylus. Penis typical with numerous glandular setae apically, each set on a protuberance. Parameres absent.

Cerci ( Fig. 149 ) first division almost glabrous except for a couple of small setae externally, second division with single ring of a few small setae and a trichobothrium, third division with a sub-basal ring of setae and trichobothria, a medial semi ring of scales and a trichobothrium and subdistally with a ring of setae, trichobothria and an external macrochaeta; fourth interval with sub-basal ring of a few setae, a trichobothrium and scales, the fifth division with three rings, the sub-basal with a seta, two trichobothria and scales, the middle ring with scales and trichobothria and the sub-distal ring with setae, macrochaetae and cilia; sixth division with four rings, the sub-basal with a seta, trichobothrium and scales, the next setae and trichobothria, the next with a trichobothrium and scales and the sub-distal with macrochaetae, cilia and setae. Subsequent divisions increase in length with eight rings visible in the most distal surviving division (eleventh).— Median dorsal appendage ( Fig. 149 ) basal divisions difficult to discern, probably only a few small setae on the most basal division; second division with a single ring of trichobothria and setae; following division with three rings, the most basal of setae and trichobothria, the following of scales only and the subdistal of trichobothria, macrochaetae and setae, fourth and fifth divisions with only two rings, the sub-basal of setae, scales and trichobothria and the subdistal of macrochaetae, setae and trichobothria, sixth division with three rings, the sub-basal of trichobothria, setae and long scales, the middle of trichobothria and shorter scales and the subdistal of macrochaetae, setae and cilia, seventh division with four rings, the sub-basal of long scales only, the next of setae and trichobothria, the third of long scales and trichobothria and the subdistal as in previous and subsequent divisions.

Female: Unknown.

Habitat. This species was collected in dry Eucalyptus leaf litter among Xanthorrhoea grass trees. Localities as in Figure 129 .

Etymology. The species is named hethicola , an artificial word referring to its habitat of heathland, using the old English word “heth” for heath and the Latin suffix “icola ” in the sense that the species is from the heath.

Figures

Figure 128. Known distribution of Acrotelsella hethicola sp. nov. from one palp. Scale bars = 0.1 mm. All arrows indicate circular sensilla.

Figure 129. Acrotelsella hethicola sp. nov. holotype from Jardine River, Queensland.

Figures 130–138. Acrotelsella hethicola sp. nov. holotype ♂ (130) periocular pectinate macrochaeta; (131) macrochaeta of prothoracic sternal comb; (132) carrot-shaped macrochaeta of tibia of PI; (133) darker scale from nota; (134) head; (135) antenna, scape, pedicel and basal intervals of flagellum; (136) idem, most distal surviving complete interval; (137) maxilla; (138) labium, chaetotaxy omitted from one palp. Scale bars = 0.1 mm. All arrows indicate circular sensilla.

Figures 139–142. Acrotelsella hethicola sp. nov. holotype ♂ (139) pronotum, left half; (140) mesonotum, left side; (141) metanotum, left side; (142) prothoracic presternum, sternum and PI. Scale bars = 0.1 mm.

Figures 143–145. Acrotelsella hethicola sp. nov. holotype ♂ (143) mesothoracic sternum and PII; (144) metathoracic sternum and PIII; (145) combs of left side of urotergite VI. Scale bars = 0.1 mm.

Figures 146–149. Acrotelsella hethicola sp. nov. holotype ♂ (146) urotergite X; (147) urosternite VI; (148) coxites IX, stylus and penis; (149) base of left cercus and median filament, with epiproct and a paraproct. Scale bars = 0.1 mm.