Acrotelsella petra, 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 : 3-12

Acrotelsella petra sp. nov.

urn:lsid:zoobank.org:act:E723F161-3F53-4BE9-B9C2-E3CDB289DBF0

Figs 2–29

Holotype ♀ (HW 1.31) QUEENSLAND: Chillagoe, Balancing Rock 17.1708°S 144.5132°E 387m asl, 23.iv.2011, Graeme Smith, under limestone stones on rocky surface, QMT259419 (on two slides) . Paratypes (11 males, three females, two juveniles) 1♂ (HW 1.15) same data as holotype, QMT259426 (on two slides) ; 1♀ (HW 0.98) Undara 18.2018°S 144.5696°E 764m asl, 28.iv.2011, Graeme Smith, underside of stone, AMS K.541650 (on two slides) ; 1♂ (HW 1.25) QLD: east of Chillagoe 17.1849°S 144.5434°E 417m asl, 17.iv.2011, Graeme Smith, Joe Sydney, Dave Rothery, under clean limestone rock, AMS K.541651 (on two slides) ; 1♀ (HW 1.45) same data as previous, AMS K.541652 (on two slides) ; 1♂ (HW 1.09) Undara , rocks above camp 18.2013°S 144.5698°E 778m asl, 5.viii.2013, Graeme & Louise Smith, leaf litter, AMS K.541654 (on two slides) ; 1 juvenile (HW 0.58) same data as previous, AMS K.377994 (in alcohol) ; 1♀ (HW 1.00) Undara , rocks above camp 18.2048°S 144.5707°E 784m asl, 5.viii.2013, Graeme & Louise Smith, leaf litter, AMS K.378030 (in alcohol) ; 1♂ (HW 1.08) Undara , rocks above camp 18.2015°S 144.5696°E 768m asl, 6.viii.2013, Graeme Smith, leaf litter on granite, K.541653 (on two slides) ; 5♂♂ (HW 1.03, 1.01, 0.95, 0.85, 0.78) 1 juvenile ♀ (HW 0.78) same data as previous, AMS K.377995 (in alcohol) ; 2♂♂ (HW 0.96, 0.90) Undara 18.2018°S 144.5696°E 764m asl, 28.iv.2011, Graeme Smith, leaf litter on granite rocks above campsite, K.377993 (in alcohol). Localities are shown on the map in Figure 2 .

Diagnosis. This species is closest to A. parlevar , sharing characters such as the three papilla of the labial palp and the parabolic shape of the thoracic sterna where some combs consist of macrochaetae in a quite irregular arrangement. It differs from A. parlevar by its broader form (width mesothorax/H+B of 0.21–0.25 versus 0.17–0.21), by the absence of combs on the inner processes of coxites IX in both sexes (sometimes seen on males of A. parlevar ), by the longer inner processes of the ♀ (L/W> 5 versus <4), by the longer ovipositor (L/HW about 2 or more, versus about 1.7) and with more divisions (24–26 versus <20), by the more acute urotergite X in both sexes (36–47° versus 47–60°), furthermore the arrangement of the macrochaetae in the thoracic sternal combs is less erratic than that seen in A. parlevar .

Description

Appearance: Medium to large silverfish, thorax not much wider than the abdomen which only tapers slightly posteriorly ( Fig. 3 ). Scale pattern when live overall dark grey or mottled when scales are lost, with lighter areas around the dorsal and lateral combs, with a distinct anterior fringe of brown macrochaetae in front of the head, legs with dark patches at apico-dorsally on femora and tibia, antennae branches are ML bootstrap values/Bayesian posterior probabilities, shown only if ≥ 70 and 0.9, respectively.

evenly brown, terminal filaments distinctly annulated with the lighter regions shorter than the darker regions especially distally. In alcohol mottled brown.

Body length: H+B up to 9.2 mm, HW up to 1.45 mm; thorax: length 3.1 mm or 0.29–0.34 H+B; width 2.3 mm with the pro and meta nota being slightly narrower than the mesonotum; maximum preserved antennal length 11.3 mm or 1.3 H+B; terminal filaments all broken, maximum preserved length of cercus 7.6 mm or>0.8 H+B; median dorsal appendage maximum length 6.3 mm (>0.8 H+B).

Pigmentation: Chestnut to brown in colour. Antennae evenly coloured brown; pigment absent from scape, pedicel with blotchy pigment which is darkest distally. Head and body dorsally almost without pigment, maxillary palp with some pigment in middle region of apical article and lighter at ends, penultimate article overall pigmented but darker distally, 3 rd article with blotchy pinkish brown pigment which is more noticeable dorsally and distally; labial palp with a little pigment on edges of ultimate and penultimate articles. Nota and thoracic sterna without obvious pigment. Coxae and trochanter of legs without pigment. Femora of PI and PII with a little pigment dorsally on distal end which is much denser on PIII, all femora also with pigment on posterior margin distal of the bulge. Tibia not strongly pigmented, just a little more distally and dorsally. Tarsi with some pigment on the basal article, most obvious on PIII. Abdominal segments without obvious pigment. Styli with quite strong chestnut pigment except for each end. Ovipositor largely without pigment. Cerci and median filament distinctly banded with only the basal and distal annuli of each division lacking pigment.

Macrochaetae: Hyaline to brown, variable, pectinate with stronger apical pectinations and numerous fine pectinations along most of the length of the shaft ( Fig. 4 ); some macrochaetae short and carrot-shaped ( Fig. 5 ) and others intermediate between these two forms.

Scales: With numerous sub-parallel ribs that do not surpass the margin of the scale ( Fig. 6 ), ribs on dorsal scales are brown, those on the ventral scales are hyaline. Scales found on top of head, clypeus, on scape, on second and third articles of maxillary palp, 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. 7 ) wider than long, with 1+1 moderately dense 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 after which there is another bush of pectinate macrochaetae almost merging with the obvious peri-antennal group, and the macrochaetae continue along the sides of the head to the eyes with the macrochaetae extending over the anterior half of the eyes in two subparallel rows. Clypeus with 1+1 very dense bushes of strongly pectinate macrochaetae as well as a few curved setae laterally anterior to the bushes; hyaline scales present between and anterior to the bushes. Labrum also with 1+1 distinct bushes of pectinate macrochaetae as well as a single long thin pectinate macrochaeta between the bushes, remainder of surface with scattered setae. — Antennae fairly long, scape ( Fig. 8 ) of average length with scales over surface and a preapical rosette of numerous setae; pedicel with preapical rosette of simple setae and cilia with two close rows of setae in places as well as setae scattered over face; annuli 1–5 of flagellum with a ring of simple setae and probably one or two short trichobothria; annuli 6–8 similar but also with some cilia. Articles subdivided into two annuli from the ninth article and into four annuli by the 13 th with the trichobothrium restricted to the most distal annulus of each interval. Distally the articles are subdivided into repeating chains of six annuli ( Fig. 9 ) each with a ring of simple setae, the third, 5 th and most distal annuli of each chain also bearing a proximal ring of setae, basiconic sensilla (type B) seen on several annuli but no distinct pattern was observed, however these can be difficult to see unless they appear on the sides of the mounted flagellum. — Mandibles typical for Acrotelsella with well-developed molar and incisor areas; a group of about thirteen strong apically bifurcated but simple setae distally adjacent to the pectinate molar area and a bush of about 120 macrochaetae externally as well as scattered simple setae and pectinate macrochaetae. — Maxilla ( Fig. 10 ) with some thick minutely apically bifurcated but otherwise smooth macrochaetae externally proximal to the palp, the lacinia with three strong teeth, one set further back than the other two, followed by about seven lamellate processes and a row of nine thin simple setae, those nearest the lamellate processes shorter and conical in shape, galea slightly longer than lacinia with about nine strong smooth simple or apically bifurcate setae externally in its basal half and several cilia distally; maxillary palp long and thin, apical article 4.2–7.1 times longer than wide and 0.9–1.1 times as long as the penultimate article, the third is the longest article, last two articles of palp with fine setae only, basal article with oblique rosette of thicker setae, second article also with subapical rosette of slightly thicker setae. — Labium ( Fig. 11 ) short and broad, prementum with transverse row of apically bifurcate setae, glossae and paraglossae with transverse and oblique rows of short strong apically bifurcated setae, apically with long curved setulae; labial palp short, apical article expanded slightly medially, usually a little longer than wide (0.95–1.35) with row of only three papillae of compact type arranged in a single row near the outer margin, with a single indeterminate basiconic sensillum and some rod-like basiconic sensilla on the outer margin, covered with numerous short and long fine setae.

Thorax: Pronotum ( Fig. 12 ) with dense setal collar about 2–3 macrochaetae wide, sometimes with very slight gap medially, macrochaetae stout and pectinate, also some cilia and many smaller stout setae; lateral margins with stout setae, marginal setae almost absent from the anterior third of the margin, becoming more frequent posteriorly, with 8–9 combs of 1–3 macrochaetae along each margin. Two open trichobothrial areas; the posterior trichobothrial area located about 0.74–0.79 along the margin and is associated with the last comb (N) this comb composed of two macrochaetae with the short trichobothrium at the mediad end and a cilium at the laterad end (the proximity of a large marginal setae close to the end of one comb on the holotype ( Fig. 13 ) gives the impression of three macrochaeta but the location of a cilium between the true comb and the marginal seta as well as the shape of the insertion supports the view that the more external macrochaeta is in fact a marginal macrochaeta rather than part of the comb); anterior trichobothrial area located 0.33–0.38 along the margin and is associated with comb N-3, the comb composed of one or two macrochaetae with the trichobothrium between the comb and the margin and a cilium at the mediad end; all combs associated with a few setulae, sometimes quite long. Posterior margin of all nota with 1+1 combs of 6–7 insertions with several setulae between the comb and the margin and a cilium at the mediad end, the most lateral insertion almost certainly houses a long thin trichobothrium-like seta; the gap between the combs on the pronotum is 45–54% the width of the pronotum. — Mesonotum ( Fig. 14 ) with lateral chaetotaxy similar to pronotum with 9–11 combs of 1–4 macrochaetae, the anterior trichobothrial area ( Fig. 15 ) located 0.61–0.66 along the lateral margin associated with comb N-2 composed of 2–3 macrochaetae (rarely one on just one side as illustrated for holotype) with the trichobothrium located between the macrochaetae and the margin, with some setulae posterior to the comb. Posterior trichobothrial area slightly more posterior than that on the pronotum (0.84–0.87), the trichobothrium located mediad of the comb of two macrochaetae and with 1–3 setulae posterior to the comb.— Metanotum ( Fig. 16 ) similar to mesonotum with 8–10 combs of 1–3 macrochaetae, the anterior trichobothrial area ( Fig. 17 ) associated with comb N-1 usually of two macrochaetae (rarely one) about 0.71–0.75 along the margin, the posterior trichobothrial area usually with two, sometimes only one macrochaeta.

Presternum narrow, with transverse row of small setae ( Fig. 18 ). — Prothoracic sternum ( Fig. 18 ) large, almost as long as the coxa, 0.93–1.12 times as long as wide at its base, parabolic, rounded apically, antero-lateral corners with fields of about 30–40 simple small setae, those on the margins finer than those submarginal, posterior three quarters of lateral margins with fringe of setae and some cilia as well as 5–9 short combs each composed of 1–13 macrochaetae mostly arranged in 2–3 overlapping rows. — Mesosternum ( Fig. 19 ) a little longer than prosternum (1.1 times) and slightly less acute apically, not much longer than wide at its base (L/ W 0.99 –1.07), without fine setae in the anterolateral corners and with long, thin simple marginal setae along the posterior quarter of the margin and 2+2, 2+3 or 3+3 combs distally, the more anterior composed of 2–16 pectinate macrochaetae in irregular rows. — Metasternum ( Fig. 21 ) much wider and shorter than mesonotum (L/ W 0.76 –0.83), apically rounded, the margins slightly concave adjacent to the posterior combs, with marginal setae and cilia along distal 1 / 5 th of lateral margins and 1+1, 1+2, 2+2 or 2+3 combs of 1–16 pectinate macrochaetae mostly arranged in single rows but with some macrochaetae offset from the rows plus some single smooth submarginal macrochaetae more distally.

Legs quite long, tibia L/W ratio of legs PI 2.4–3.7, PII 2.7–4.1, PIII 3.3–4.2; tarsi L/W ratio PI 5.1–7.0, PII 5.5–8.9, PIII 9.3–10.3. PI ( Fig. 18 ) with a row of about five macrochaetae laterally on the distal margin of the precoxa. Coxa with scales and a group of about fifteen macrochaetae on the anterolateral corners arranged in two irregular rows, followed by a field of strong pectinate macrochaetae along the external margin; inner margin with a five macrochaetae and several smooth and pectinate setae of varying thickness distally over the articulation. Trochanter with many small setae and cilia as well as a single pectinate macrochaeta. Femur posteriorly with several long thin pectinate macrochaetae and smooth setae along the margin, most individuals without carrot-shaped macrochaetae (although these may have been lost during handling), considerable variation exists between individuals with some only having thinner macrochaetae, others of intermediate thickness and a couple of specimens show at least one distinctly carrot-shaped macrochaeta; dorsal margin with three macrochaetae towards the distal end. Tibia of PI with about four stout, carrot-shaped slightly pectinate macrochaetae along the posterior margin as well as some thinner smooth setae and a row of shorter setae near the distal margin; anterior margin with two pectinate macrochaetae as well as some subdistal setae over the articulation, dorsal surface with a subdistal row of setae; 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, the surface of all tarsal articles with numerous simple setae. Pretarsus with two long curved lateral claws and a shorter curved medial claw. PII and PIII ( Figs 20–21 ) similar to PI except lacking the antero-lateral groups of macrochaetae on the coxa; femora with more carrot-shaped macrochaetae on the posterior margins; legs progressively longer from PI to PIII and the relative length of the basal tarsal article is progressively longer but only about 60% of the total length on PIII; tibia of PIII bearing a long thin trichobothrium-like seta adjacent to the more proximal macrochaeta near the dorsal margin.

Abdomen: Urotergite I with 1+1 lateral combs of 5–6 macrochaetae each associated with a cilium at either end and several setulae between the comb and the margin, urotergites II–VII ( Fig. 22 ) with 3+3 combs of macrochaetae as in Table 3, the lateral combs with a cilium at either end, the sublateral comb with a cilium at either or both ends, the submedial with a cilium at the outer end and several setae or setulae between the comb and the margin. Urotergite VIII with 2+2 combs (lacking the sublateral), urotergite IX glabrous; urotergite X ( Fig. 23 ) acutely triangular, slightly more acute in the female (36–45°) than in the male (42–47°), wider at base than long (L/ W 0.7 –1.0) with many setae along entire margin both above and below (small, simple or slightly pectinate) and four to six combs of 1–6 macrochaetae per comb as well as several setulae posterior to each comb, most combs with a cilium at the mediad end.

Urosternite I and II glabrous, urosternites III–VII with 1+1 lateral combs of 9–18 pectinate macrochaetae ( Fig. 24 ) each with several setulae or setae between the comb and the margin as well as a cilium at each end of every comb. The distance between the lateral combs 3.0–6.2 times the average width of the combs, the ratio being largest on urosternite III and decreasing posteriorly.

Genital region of ♀ as in Figure 26 . Two pairs of styli with very numerous stronger macrochaetae apically as well as quite numerous setae and some scales along the shaft. Coxites VIII with long combs of 11–15 macrochaetae and a similar number of setae and setulae between the comb and the margin, the coxites with rounded inner corners. Coxites IX with long rounded internal process about 5.9 times longer than wide at its base and thirteen times longer than the short pointed external process, the inner processes not reaching the apex of the ovipositor; outer process with several setae externally, inner process with several long smooth setae along the outer margins as well as finer setae, inner margin of process with setae insertions (all setae lost) and many small setae or setulae, apically with several long smooth setae. — Ovipositor ( Fig. 26 ) quite long (2.0–2.2 HW), surpassing the apex of the long internal processes of coxites IX, both pairs of gonapophyses consisting of longer basal articles becoming progressively shorter distally, about 24–26 articles in total; of primary type with rows of fine setae on each article.

Cerci ( Fig. 27 ) first division with some small insertions laterally, divisions two to four with single rings of setae, trichobothria and a lateral pectinate macrochaeta, divisions five to seven with two rings, the basal of scales and trichobothria, division eight with three rings, the basal of setae, trichobothria and scales, division nine with four rings with scales on the basal and penultimate rings. Most distal surviving divisions with ten annuli each with a ring of setae, the most distal and one and a half of the most basal without strong pigment, macrochaetae restricted to the distal ring, rings 3, 5, 8 and 10 with cilia, rings six and seven with trichobothria ( Fig. 29 ). — Median dorsal appendage ( Figs 27–28 ) first article glabrous, articles two to five with single rings of setae, trichobothria and macrochaetae, divisions six and seven with two rings the basal probably also with scales, division eight with three rings, the middle one of scales, division nine with four rings, with scales found on the basal and penultimate rings. Most distal surviving divisions (mid length) similar to cerci but lighter region restricted to the distal annulus only, scales found on the basal part of annuli 3–6, trichobothria on annuli 2, 5 and 6.

Male. Similar to female except coxites VIII entire ( Fig. 25 ) with 1+1 combs of macrochaetae. Coxites IX in ♂ separated, each side with a macrochaeta insertion mediad to the base of each stylus. External and internal margins of internal process with some moderately strong setae and macrochaetae; ventral surface of process with many long thin setae inserted parallel to the external margin. No short transverse combs found. Outer process small triangular with several stout setae along the outer margin. Penis typical with numerous glandular setae apically, each set on a protuberance. Parameres absent.

Habitat. Collected from the underside of limestone rocks at Chillagoe and from dry leaf litter on granite rock slopes at Undara. Localities as in Figure 2 .

Etymology. The species is named petra from the Latin word for rock, because it was collected on the underside of rocks and from dry leaf litter accumulated on large rocky exposures.

Figures

Figure 2. Known distribution of Acrotelsella petra sp. nov.

Figure 3. Acrotelsella petra sp. nov. from Balancing Rock, Chillagoe, Queensland.

Figures 4–11. Acrotelsella petra sp.nov.holotype ♀ unless otherwise indicated by specimen number (4) pectinate peri-ocular macrochaeta; (5) pectinate macrochaeta of posterior margin of femora of PI; (6) darker scale of pronotum; (7) head (cross-hatched area obscured by eye pigment); (8) antenna, scape, pedicel and basal intervals of flagellum of QMT259426; (9) idem, most distal surviving complete interval; (10) maxilla; (11) labium, smaller chaetotaxy and papillae omitted from one palp (K.541651). Scale bars = 0.1 mm.

Figures 12–20. Acrotelsella petra sp. nov. holotype ♀ unless otherwise specified by specimen number (12) pronotum, right side (QMT259426); (13) pronotum,posterior trichobothrial area, rightside with unusually aligned marginal macrochaeta;(14) mesonotum, right side (QMT259426); (15) mesonotum, anterior trichobothrial area, right side (QMT259419); (16) metanotum, right side (QMT259426); (17) metanotum, anterior trichobothrial area, right side (QMT259419); (18) prothoracic presternum, sternum and PI; (19) mesothoracic sternum; (20) PII. Scale bars = 0.1 mm.

Figures 21–25. Acrotelsella petra sp. nov. holotype ♀ unless otherwise indicated by specimen number (21) metathoracic sternum and PIII; (22) urotergite VI, left side; (23) urotergite X; (24) urosternite VI, left side; (25) coxites IX and penis (QMT259426). Scale bars = 0.1 mm.

Figures 26–29. Acrotelsella petra sp. nov. holotype ♀ unless otherwise indicated by specimen number (26) left coxites VIII and IX with ovipositor; (27) base of left cercus with epiproct and a paraproct (QMT259426); (28) base of median filament (QMT259426); (29) most distal surviving division of cercus (QMT259426). Scale bars = 0.1 mm.