Acrotelsella thommoi, Smith & Mitchell, 2022

Smith, Graeme B. & Mitchell, Andrew, 2022, On some Silverfish Taxa from the Mildura Region (Inland South-eastern Australia) (Zygentoma: Lepismatidae: Ctenolepismatinae), Records of the Australian Museum (Rec. Aust. Mus.) 74 (5), pp. 151-199 : 181-188

Acrotelsella thommoi sp. nov.

urn:lsid:zoobank.org:pub:7F1EA4F4-20EE-4B14-B588-6F1381D21E0F

Figs 98–123

Holotype ♀ ( HW 1.45 ) NEW SOUTH WALES: ca 55km northwest of Nyngan 31.14635°S 146.8123°E 251m asl, 7.iv.2011, Graeme Smith, in accumulated bark/termite dirt in fork at base of Eucalypt; also under bark at very base, AMS K.541636 (on two slides) . Paratypes 1♂ ( HW 1.50 ), same data as holotype, AMS K.541637 (on two slides) ; 1♂ ( HW 1.43 ), same data as holotype, AMS K.377973) (in alcohol) .

Other material examined but not included in type series. 1♂ ( HW 1.29 ) VICTORIA: Hattah-Kulkyne N.P. 34.62633°S 142.37472°E 75m asl, 24.ix.2013, Graeme Smith, top of dune in loose strips of bark caught in fork of Eucalyptus, NMV gbs004035 (on two slides); 1♀ ( HW 1.25 ) Hattah-Kulkyne N.P. 34.62636°S 142.37486°E 71m asl, 24.ix.2013, Graeme Smith, bark spray to loose strips of bark caught in fork of Eucalyptus, NMV gbs004036 (on two slides) .

Diagnosis. This species can be distinguished from other described Acrotelsella with a primary type ovipositor and a rounded or slightly pointed subtriangular prothoracic sternum by a combination of several characters including the presence of three papillae in a straight line, by the presence of only a single macrochaeta mediad of the anterior trichobothrium on the meso- and metanota, by the quite rounded posterior margin of coxites VIII in the female (the curved region occupying ⅔–⅞ of the margin versus less than half in other Australian species but possibly about the same as in A. wygodzinskyi Hazra, 1980 from India and A. giubana from Somalia), by the larger number of divisions in the ovipositor (25–31 versus less than 25 in all other described species).

Description

Appearance: Medium to large silverfish, with narrow body, thorax slightly wider than the abdomen which only tapers slightly posteriorly. Scale pattern when live mottled grey, with light brown macrochaetae ( Fig. 99 ); in alcohol mottled brown. Eyes dark chestnut, thorax and abdomen dorsally fairly evenly covered in brown scales.

Body length: H+B up to 11.3 mm, HW 2.4 mm; thorax: length 3.5 mm or 0.29–0.35 H+B; width 2.4 mm with the mesonotum being slightly wider than the pronotum and metanotum. Antennae when complete up to about H+B; terminal filaments maximum length seen of 0.87 H+B.

Pigmentation: Flagellum of antennae without annulations, light brown pigment evenly distributed; scape and pedicel without pigment. Head with slight pigment behind the eyes, ultimate article of maxillary palp with light pigment at each end, moderate brown pigment on other four articles, mostly along the sides and above (not below); labial palp with similar moderate pigment on articles 2–3, ultimate article with pigment only along proximal margins. Nota and thoracic sterna without obvious pigment. Coxae of legs with light pigment along the outer margin. Trochanter with slight pigment in distal corner adjacent to femur. Femora with small pigment region over posterior bulge extending to the joint with the tibia as well as on the leading edge adjacent to the distal comb. Tibia dark along dorsal margin especially distally but at least some of this is due to scales. First tarsal article dark with pigment and scales, remaining articles without pigment. Abdominal segments without obvious pigment except for pigment on coxites IX adjacent to the styli. Ovipositor largely without pigment. Cerci and median filament with medium brown pigment overall, except for the distal most annulus of each division bearing the large macrochaetae which is light in colour, this lighter area can be less prominent in some individuals.Abdominal styli with light pigment.

Macrochaetae: Variable, the major macrochaetae of the combs with strong pectinations ( Fig. 100 ) while those of the larger slightly submarginal macrochaetae have more delicate pectinations, less numerous apically ( Fig. 101 ) or smooth, straw coloured.

Scales: Variable in shape, with numerous sub-parallel ribs that do not surpass the margin of the scale ( Fig. 102 ), those dorsal are brown, those ventral hyaline. Scales found on top of head, on scape, on second and third articles of maxillary palp, on mentum of labium, all nota, all thoracic sterna, legs (except for trochanter and distal three articles of tarsi), all urotergites and urosternites, styli IX, medial filament and cerci.

Head: ( Fig. 103 ) wider than long, with 1+1 bushes of macrochaetae aligned in subparallel rows on the antero-lateral corners. Eyes dark brown in alcohol preserved material. There is a small gap in the row of macrochaetae along the margin above the antennal bases behind which is another row of macrochaetae two macrochaetae wide which extends to and above the eyes; the peri-antennal group is almost connected with the lateral rows. Clypeus with 1+1 very dense bushes of strongly pectinate macrochaetae as well as a few setae laterally. Labrum also with 1+1 dense bushes of pectinate macrochaetae as well as many simple setae, some longer than others. —Antennae fairly long, scape ( Fig. 104 ) quite long with scales over surface and a preapical ring of numerous setae; pedicel with preapical ring of strong simple setae and cilia as well as smaller setae on the dorsal face and some scattered over face; first annulus/interval of flagellum glabrous; next annulus in holotype apparently with three rings of simple setae each with a trichobothrium which probably represent annuli in the process of dividing; subsequent four intervals with single ring of setae and cilia and a short trichobothrium per annulus; following interval divided into two with the basal annulus glabrous and the next of setae, cilia and a trichobothrium. By one quarter the length of the antennae there are four annuli per interval and by mid antenna eight per interval. Distally it is difficult to decide how many annuli per interval as the trichobothria do not appear to be present. There is a repeating pattern of six annuli ( Fig. 105 ) with the most distal annulus having at least one long basiconic sensilla type B and probably also a campaniform sensilla. — Mandibles ( Fig. 106 ) typical for Acrotelsella with prominent molar and large incisor areas; a group of about nine strong apically bifurcated but simple setae distally adjacent to the pectinate molar area and a bush of extremely numerous and densely packed pectinate macrochaetae externally as well as scattered simple setae. — Maxilla ( Fig. 107 ) with two thicker and one smaller, smooth or slightly pectinate macrochaeta externally proximal to the palp, the lacinia with four strong teeth, one set further back than the other three, followed by seven lamellate processes and a row of six smooth apically bifurcate setae, galea longer than the lacinia with just two somewhat stronger, smooth, simple or apically bifurcate setae externally in its basal half and several cilia distally; maxillary palp long and thin, apical article 3.6–6.1 times longer than wide and 0.93–1.07 times as long as the penultimate article which is almost as long as the third and longest article, the ultimate article apparently only with basiconic sensilla (type B); last two articles of palp with fine setae only, third article with scales and thin setae as well as a few slightly stronger setae subapically, first and second articles with subapical ring of slightly thicker setae, the ring incomplete on the basal article, second article also with scales. — Labium ( Fig. 108 ) short and broad, postmentum with transverse row of simple and truncate apically bifurcate macrochaetae, prementum with transverse and oblique rows of short strong apically bifurcated setae, apically with curved setulae; labial palp with the second article with several strong setae; apical article expanded medially, a little shorter than long (0.79–1.04) with row of three papillae of compact type arranged in a single row near the outer margin, with one or two rod-like basiconic sensillum (type B) near the outer margin, covered with numerous fine setae as well as longer fine setae.

Thorax: Pronotum ( Fig. 109 ) with setal collar about three macrochaetae wide, with the macrochaetae in the medial region smaller and sparser than those laterally; lateral margins with a few smaller finely pectinate setae along the margin, as well as larger slightly submarginal macrochaetae also with subtle pectinations, usually located near to but not quite in line with the lateral combs, with 8–9 combs of one to three strongly pectinate macrochaetae along each margin. Two open trichobothrial areas; the anterior trichobothrial area about 0.34–0.39 of the distance along the margin, associated with comb N-3, the trichobothrium being placed between the single macrochaeta of the comb and the margin; posterior trichobothrial area is located about 0.70–0.75 of the distance along the margin and is associated with the last comb which is composed of two macrochaetae with the short trichobothrium at the mediad end and a cilium at the laterad end, all combs associated with a several setulae. Posterior margin with 1+1 combs of 4–8 insertion points, each associated with a few small setae between the comb and the margin and a cilium at each end; the outermost insertion on the comb is occupied by a long thin trichobothrium-like seta. The gap between the posterior combs 48–49% of the width of the pronotum. — Mesonotum ( Fig. 110 ) with lateral chaetotaxy similar to pronotum but with 9–11 combs each of 1–4 macrochaetae, the anterior trichobothrial area located 0.60–0.65 along the lateral margin associated with comb N-2 composed of one macrochaeta (rarely two) with the trichobothrium located between the macrochaeta and the margin, with several setulae posterior to the comb and a cilium at the mediad end. Posterior trichobothrial area slightly more posterior than that on the pronotum (0.82–0.84), the trichobothrium located mediad to the comb of usually just one macrochaeta although two occur on one side of gbs004036 and with a few setulae posterior to the comb. Posterior margin with 1+1 combs of 4–8 macrochaetae insertions usually with a cilium at each end, the most lateral macrochaeta most likely a long, thin, trichobothrium-like seta, with a few setulae between the comb and the margin. — Metanotum ( Fig. 111 ) similar to mesonotum with 8–10 combs of 1–4 macrochaetae, the anterior trichobothrial area associated with comb N-1 of two macrochaetae about 0.72–0.73 along the margin, the posterior trichobothrial area associated with the most posterior comb (0.85–0.87 along margin) and the posterior 1+1 combs each of 4–8 macrochaetae, the most lateral macrochaeta being long, thin and trichobothrium-like, with a few setulae between the comb and the margin.

Presternum very narrow, with transverse row of long almost smooth setae and setulae ( Fig. 112 ). — Prothoracic sternum ( Fig. 112 ) large, 0.93–1.07 times as long as wide at its base, parabolic, rounded apically, antero-lateral corners with many simple setae, those on the margins smaller than those just inside the margin, posterior ⅘ to ⅔ of lateral margins with fringe of long setae and some cilia as well as 4–7 combs each composed of 1–6 pectinate macrochaetae arranged in single straight or curved combs. — Mesosternum ( Fig. 113 ) a little larger than prosternum (1.10–1.16 times as long) but similar in shape, about a long as wide at its base (L/ W 1.00 –1.02), with a few fine setae in the anterolateral corners, with long, thin simple marginal setae and cilia along the posterior quarter of the lateral margins and 2 + 2 combs distally, the more anterior composed of 5–6 strongly pectinate macrochaetae, the next of 4–5 macrochaetae with additional slightly submarginal 1+1 strong setae nearer to the posterior end; all combs with a few setulae distal to each comb. — Metasternum ( Fig. 114 ) shorter and wider than the mesosternum (L/ W 0.77 –0.82) apically rounded or very slightly pointed, the margins may be slightly concave adjacent to the posterior combs, with marginal setae and cilia along distal margins adjacent to the combs as well as a few setulae between the combs and the margin; 1+1, 1+2 or 2+2 subdistal combs of 2–11 strongly pectinate macrochaetae.

Legs of average dimensions, neither long and slender nor short and stout, tibia L/W ratio of PI 2.5 (range 2.2–2.9), PII 2.9 (range 2.7–3.3), PIII 5.0 (range 3.3–6.0); tarsi L/W ratio PI 6.0 (range 5.4–7.2), PII 6.8 (range 5.8–8.0), PIII 8.6 (range 7.0–10.4). PI ( Fig. 112 ) with a row of about six macrochaetae laterally on the precoxa. Coxa with scales and a group of about eight macrochaetae on the anterolateral corners followed by a field of pectinate macrochaetae along the external margin about three macrochaetae wide; inner margin with a five lightly pectinate macrochaetae and several smooth and pectinate setae of varying thickness distally over the articulation; distal end with distinct cleft, with a row of small setae along the mediad margin. Trochanter with one small pectinate macrochaeta and a few strong smooth setae. Femur posteriorly with several slender pectinate macrochaetae, in addition to some stronger tapered and carrot-shaped macrochaetae along the margin to the posterior bulge then a row of about eight setae along the margin to the articulation; anterior edge with two strong macrochaeta insertions near the articulation. Tibia of PI with about two stout, carrot-shaped, pectinate macrochaetae along the posterior margin as well as several longer, thinner, pectinate or smooth setae and a row of three shorter stout setae near the distal margin; anterior margin with two strong insertion points about ½ and ¾ along the margin, each associated with one or two strong setae, as well several subdistal setae over the articulation; apex of tibia with the usual apical spur which is covered in numerous 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, whereas the distal margin of the second article is quite oblique, the surface of all tarsal articles with very numerous simple setae. Pretarsus with two long curved lateral claws and a shorter curved medial claw. PII ( Fig. 115 ) and PIII ( Fig. 116 ) similar to PI except the macrochaetae laterally on the coxae are somewhat reduced in the anterior half on PII and much reduced in the anterior half on PIII; the tibia of PIII has a long thin trichobothria-like seta about ¼ the distance along the outer margin: legs progressively longer from PI to PIII and the relative length of the basal tarsal article is progressively longer, being about 60% of the total length of the tarsus of PIII.

Abdomen: Urotergite I with 1+1 lateral combs of 5–7 macrochaetae each associated with a cilium at each end and several setulae or slender setae between the comb and the margin, urotergites II–VII with 3+3 combs of 4–13 macrochaetae as in table 6 ( Fig. 117 ), urotergite VIII with 2+2 combs (lacking the sublateral), urotergite IX glabrous; all combs with a cilium at each end and many small setae and setulae between the comb and the margin. — Urotergite X ( Fig. 118 ) triangular (50–56° in both sexes) but with the apex slightly withdrawn from the apex of a triangle, wider at base than long (L/ W 0.60 –0.77) with many delicately pectinate smooth setae along entire margin both above and 4–5 combs on each side, the combs composed of 1–7 macrochaetae per comb usually with a cilium at the mediad end of each comb, as well as several setulae posterior to each comb.

Urosternite I and II glabrous, urosternites III–VII with 1+1 lateral combs of 8–17 pectinate macrochaetae ( Fig. 119 ) each with a similar number of setulae between the comb and the margin as well as a cilium at the lateral end of every comb. The distance between the lateral combs 3.5–10.3 times the average width of these combs, the ratio being largest on urosternite III and decreasing posteriorly.

Genital region of ♀ as in Figure 120 . Two pairs of styli, those on IX about one third longer than those on VIII, with some robust setae apically. Coxites VIII with long combs of 10–14 macrochaetae and a smaller number of thin but sometimes very long setae (almost as long as the macrochaetae) between the comb and the margin, the coxites with rounded inner corners, the straight section being only ⅛–⅓ the width of the distal margin. Coxites IX with long rounded internal process, about 2.8–5.2 times longer than wide at its base (longer in larger specimens) and 7.2–11.4 times longer than the short pointed external process, the inner processes surpassing the apex of styli IX including macrochaetae, almost reaching to the end of the ovipositor; outer process with several setae externally, inner process with strong smooth macrochaetae along the margins, being very dense on the outer margin where many scales also exist. — Ovipositor of primary type with rows of fine setae on each article ( Figs 120, 121 ), not very long (up to 1.5 HW, range 1.42–1.95), reaching to the apex of the long internal processes of coxites IX, both pairs of gonapophyses consisting of long basal division followed by smaller divisions that do not differ greatly in their length along the ovipositor, 25–31 divisions in total.

Cerci ( Fig. 122 ) with first division almost glabrous, with just a couple of minute setae near the lateral margin, following four divisions wider than long with two or three rings of setae, macrochaetae and trichobothria, the middle, later also most basal ring with some small scales, divisions then progressively longer with four annuli per division each with a ring of setae, trichobothria, macrochaetae restricted to the most distal ring, scales present in the most basal and the penultimate rings.— Median dorsal appendage ( Fig. 122 ) first division glabrous, second division very short with only a couple of small setae laterally on each side, third division with one full ring, following two divisions with a single ring of setae and trichobothria, subsequent divisions with two or more rings of setae and trichobothria with scales present on basal and middle rings. Most distal divisions in more or less intact terminal filaments with 16 annuli per division. Epiproct and paraprocts quite darkly sclerotized or pigmented.

Coxite VIII in ♂ entire with 1+1 combs of 11–15 macrochaetae as well as many thin marginal setae and setulae between the comb and the margin. Coxites IX in ♂ separated ( Fig. 123 ) each side with a long smooth macrochaeta (about ⅔ the length of the internal process) mediad to the base of the stylus. The internal process very acute apically, about 2.9–4.8 times longer than the external process and 1.3–1.5 times as long as broad at its base. External and internal margins of internal process and external margin of outer process with many finely pectinate setae and macrochaetae. Outer process small triangular with several stout finely pectinate setae along the outer margin. Penis typical with numerous glandular setae apically, each set on a protuberance. Parameres absent.

Habitat. This species has been collected in accumulated bark and/or termite dirt in fork at base of Eucalypt, as well as under bark at very base of Eucalypt.

Etymology. This species is named for a good friend, Greg Thompson (“Thommo”), a quiet adventurer, who sadly is no longer with us (22 January 1954 – 22 October 2021).

Remarks

There are several species in a group that have simple ovipositors and, while we have found distinct morphological differences to separate the three species described in this work, it is quite difficult to be certain of the position of other species described because of their inadequate descriptions. Acrotelsella splendens (Nicholls and Richardson, 1926) appears to differ from the three species described in this work by the extremely truncate posterior margin to coxites VIII with less than one quarter of the margin being occupied by the medio-posterior curve. It is also illustrated as having a long series of papillae on the labial palp whereas the species described here do not have more than five papillae. However, Mendes (1989) redescribed the species based on material from Indonesia and Thailand without seeing the type material. Only five papillae are illustrated on the ultimate article of the labial palp and Mendes does not illustrate the posterior margin of coxites VIII in the female. The variability of the shape of urotergite X between the Thai and Indonesian specimens is much greater than we have found within species in this current study. While the material described by Mendes may be closely related to the Australian species, we believe that their correct identity needs further investigation. We have not included the characters described by Mendes in our evaluation of the species described here.

Acrotelsella producta also appears in this group but the inner processes of coxites IX are illustrated, at least in one of his illustrations, as being much longer than any other species, reaching beyond the apex of the stylus IX by the length of the stylus, however it is not illustrated as being so long in a second illustration in the tables. No other described species extends more than half the length of stylus IX, however Acrotelsella producta does need to be redescribed, checking the length of the processes as well as providing details on many characters, over-looked at that time but now considered relevant. Womersley (1939) interpretation of the various specimens before him and his interpretation of the published descriptions of other Acrotelsella species is probably not very helpful and should be re-examined in the light of new knowledge and technical advances.

Acrotelsella pacifica may also fit into this group of species. It differs from all other species in the group by having 8–14 labial palp papillae however the original description of Marquesas Island material lacks many details and Mendes (1989) supplementary description is based on material from Indonesia and the Philippines without reference to the types and also lacks some details that we now think useful .

Figures

Figure 98. Known distribution of Acrotelsella thommoi sp. nov.

Figure 99. Acrotelsella thommoi sp. nov., Nyngan.

Figures 100–108. Acrotelsella thommoi sp. nov. holotype ♀ (100) long pectinate macrochaeta of clypeus; (101) finely pectinate marginal macrochaeta of pronotum; (102) darker dorsal scale of mesonotum; (103) head (cross-hatched area obscured by eye pigment); (104) antenna, scape, pedicel and basal intervals of flagellum; (105) idem, most distal surviving complete interval; (106) mandible; (107) maxilla; (108) labium. Scale bars = 0.1 mm.

Figures 109–112.Acrotelsella thommoisp.nov.holotype ♀ (109) pronotum,rightside;(110) mesonotum,rightside with anterior trichobothrial area indicated; (111) metanotum with trichobothria indicated; (112) presternum, prothoracic sternum and PI. Scale bars = 0.1 mm.

Figures 113–116. Acrotelsella thommoi sp. nov. holotype ♀ (113) mesothoracic sternum; (114) metathoracic sternum; (115) PII; (116) PIII. Scale bars = 0.1 mm.

Figures 117–123. Acrotelsella thommoi sp. nov. holotype ♀ unless otherwise indicated by specimen number (117) urotergite VII, left half; (118) urotergite X; (119) urosternite VII, left half; (120) left coxites VIII and IX with styli and ovipositor; (121) apex of gonapophyses; (122) base of cerci and medial filament; (123) right coxite IX of male and penis (K.541637). Scale bars = 0.1 mm.