Acrotelsella obscura, 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 : 59-66

Acrotelsella obscura sp. nov.

urn:lsid:zoobank.org:act:C6FF0E0D-7BD7-47A3-AE56-BEFCB789EEED

Figs 176–199

Holotype ♀ (HW 1.25) QUEENSLAND: south of Coen 14.1442°S 143.2451°E 238m asl, 1.viii.2013, Graeme & Louise Smith, leaf litter, QM T259423 (on two slides) . Paratypes (one male, one female) 1♀ (HW 1.13) same data as holotype, AMS K.541677 (on two slides) ; 1♂ (HW 1.30) same data as holotype, QM T259430 (on two slides)

( Fig. 176 ). Diagnosis. This species can be distinguished from other described species with secondary ovipositors by the expanded outer margins on the inner processes of coxites IX in the female being 1.5 times wider at their widest point than at their base (versus 0.9–1.2 in all other species of the group where this has been measured e.g., A. obscura sp. nov., A septentrionalis sp. nov., A. mallee , A. albicaudata ), the presence of only two macrochaetae (rarely three) in the posterior trichobothrial areas of all nota and the presence of several exceptionally long finely pectinate macrochaetae along the shaft of styli IX.

Description

Appearance: Medium sized silverfish, somewhat stocky in form, thorax wider than the abdomen. Scale pattern when live see Figure 177 , antennae evenly brown, terminal filaments annulated, slightly darker scales on back of head. In alcohol specimens become very dark almost as soon as they contact the alcohol.

Body length: H+B up to 8.9 mm, HW 1.30 mm; thorax: length 2.4 mm or 0.27–0.31 H+B, width 2.3 mm with the mesonotum being slightly wider than the pronotum. Antennae incomplete, maximum preserved length 5.9 mm or>0.77 H+B; terminal filaments all broken, maximum length of terminal filaments 4.4 mm or>0.5 H+B.

Pigmentation: Cuticle overall quite dark with specimens becoming very dark when placed into alcohol. The intensity of darkness makes it difficult to observe macrochaetae insertions in some places. Some variability in darkness noted between specimens. Flagellum of antennae without banding, moderate orange-brown pigment evenly distributed; pedicel and scape with pigment distally. Frons overall slightly dark, labrum and clypeus without pigment, mandibles and maxillae overall slightly pigmented but without strong pigment among bushes of macrochaetae, maxillary and labial palps with stronger brown pigment, the distal article of the maxillary palp overall with medium brown pigment, penultimate and third articles with moderate pigment overall but darkest distally, second article also with moderate pigment but lighter at base. Labial palp ultimate and penultimate articles with quite dark pigment, especially around edges. Nota and thoracic sterna without obvious pigment. Shoulder of the coxa darker but not along the outer margin. Trochanter with pigment along outer margin more pronounced at each end. Femora fairly evenly well pigmented, darker at the anterior distal corners. Tibia darkly pigmented overall, except for apical spur. First tarsal article with more pigment distally, distal article with some light orange pigment apically. Abdominal segments progressively darker towards posterior end (sclerotised or pigment?); coxites VIII and IX quite dark. Ovipositor a little pigmented distally. Cerci and median filament annulated, mostly dark divisions except for first annulus which is light in colouring and apex of distal division distad of the ring of macrochaetae. Abdominal styli darker in distal half becoming more intense distally, styli VIII the same or sometimes with much less pigment.

Macrochaetae: Variable strongly pectinate ( Figs 178–180 ) carrot-shaped and strongly pectinate or more subtly pectinate curved and tapered dark brown to straw coloured.

Scales: With numerous sub-parallel ribs that do not surpass the margin of the scale ( Fig. 181 ), those dorsal are brown, those ventral brown or hyaline. Scales found on top of head, on pedicel and scape, mandible, 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 and terminal filaments.

Head: ( Fig. 182 ) 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 chestnut in alcohol preserved material. There is a small gap behind each bush in the row of macrochaetae along the margin which extends inwards towards but not quite reaching the peri-antennal group and its long thin trichobothrium-like seta; the marginal row continues back and up over the eyes about two macrochaetae wide. Clypeus with 1+1 very dense bushes of strongly pectinate macrochaetae as well as a few curved setae laterally. Labrum also with 1+1 dense bushes and a single macrochaeta and scattered cilia medially between the bushes as well as some simple setae scattered over the face. — Antennae fairly long, scape ( Fig. 183 ) not long with scales over much of its surface and a preapical ring of setae; pedicel with preapical ring of simple setae and cilia as well as scales over face; first annulus/interval of flagellum with a weak subapical ring of simple setae; second to sixth annuli with ring of simple setae each and at least one trichobothrium; interval seven also with a cilium in the ring of setae and a trichobothrium; intervals eight and nine divided into two annuli, the basal of setae only the subdistal with two trichobothria and some cilia; interval ten divided into three annuli and interval eleven into four annuli with the trichobothrium restricted to the most distal annulus.At about half the length of the antennae the intervals are subdivided into about nine with the most distal annulus bearing a proximal ring of setae, a subapical ring of cilia and two trichobothria; rod-like basiconic sensilla (type B) rarely seen. Most distal surviving intervals difficult to define ( Fig. 184 ) perhaps divided into seven annuli with trichobothria no longer observed, basiconic sensilla type B seen on ultimate annulus; circular sensilla were not seen but may be present as the darkness of the antennae makes observation very difficult. — Mandibles typical for Acrotelsella with well-developed molar and incisor areas; a group of about 10–15 strong apically bifurcated but simple setae distally adjacent to the pectinate molar area and a bush of around eighty strong, often dense, pectinate macrochaetae externally as well as scattered simple setae. — Maxilla ( Fig. 185 ) with one or two stout smooth macrochaetae as well as 2–3 smaller setae 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 5–7 short simple setae, galea longer than lacinia with about 3–5 strong, smooth simple or apically bifurcate setae externally in its basal half and several cilia distally; maxillary palp very long and thin, apical article 6.0–6.2 times longer than wide and about the same length as the penultimate and third articles, the ultimate article with a small basiconic (type B) and fine setae, penultimate and third articles with some slightly thicker setae subdistally, second and third articles also with scales, first and second articles with more distal subdistal rings of stronger setae. — Labium ( Fig. 186 ) short and broad, postmentum with transverse row of strong apically bifurcate and simple setae, prementum with transverse and oblique rows of stout apically bifurcated setae, apically with long curved setulae; labial palp short, apical article slightly expanded medially with a row of 10–11 papillae of compact type arranged in a single curved row, with one or two very small rod-like basiconic sensilla (type B) on the outer margin, covered with numerous fine setae as well as longer fine setae.

Thorax: Pronotum ( Fig. 187 ) with dense setal collar of both longer and shorter strongly pectinate macrochaetae about 2–3 macrochaetae wide, without slight medial gap; lateral margins with many strong shorter and longer curved slightly pectinate macrochaetae as well as a few cilia, with 9–10 combs of 1–4 macrochaetae along each margin. Two open trichobothrial areas; the posterior trichobothrial area located about 0.72–0.73 along the margin and is associated with the last comb (N), this comb composed of two (sometimes three) macrochaetae with the short trichobothrium at the mediad end and a cilium at the laterad end, the anterior trichobothrial area forward of the midpoint (0.36–0.43) 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; however on many specimens, a large lateral macrochaeta is aligned with this comb giving the impression of the trichobothrium being positioned between two macrochaetae, all combs associated with a few setulae, sometimes more numerous. Posterior margin of all nota with 1+1 combs of 5–7 macrochaetae insertions associated with several setulae between the comb and the margin and a cilium at each end, the macrochaetae are mostly lost but in several specimens (probably all) the most laterad or second most laterad is occupied by a long thin trichobothrium-like macrochaeta; these combs not widely spaced (gap between them 46–49% of total width of pronotum). — Mesonotum ( Fig. 188 ) with lateral chaetotaxy similar to pronotum with ten combs of 1–4 macrochaetae, the anterior trichobothrial area located 0.57–0.61 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 (0.82–0.83) the trichobothrium located mediad to the comb usually of two macrochaetae and with 1–3 setulae or stronger setae posterior to the comb.— Metanotum ( Fig. 189 ) similar to mesonotum with nine combs of 1–4 macrochaetae, the anterior trichobothrial area associated with comb N-1 of a single macrochaeta about 0.74 along the margin, the trichobothrium located between the margin and the macrochaeta, the posterior trichobothrial area associated with the most posterior comb (0.87–0.88 along the margin) of two macrochaetae.

Presternum narrow, with transverse row of spaced pectinate macrochaetae and setae, without numerous fine setulae below and between these macrochaetae ( Fig. 190 ). — Prothoracic sternum ( Fig. 190 ) parabolic, a little shorter than at its base (L/ W 0.89 –0.96) antero-lateral corners with about 10–15 simple marginal setae, posterior three quarters of lateral margins with fringe of setae and some cilia as well as 6–9 short combs on each side each composed of 2–9 pectinate macrochaetae, combs sometimes lying quite close to each other and lying in two overlapping rows, sometimes with a strong seta on the margin near the end of the comb but not counted in the number of macrochaetae per comb, these strong marginal or submarginal smooth macrochaetae also present distally and at irregular locations along the lateral margins. — Mesosternum ( Fig. 191 ) only a little larger than prosternum (1.1–1.2 times as long) about as long as wide at its base (L/ W 1.00 –1.12) anterolateral corners glabrous, posterior third of margins with many long thin setae and 3+3 combs distally, each composed of 5–11 pectinate macrochaetae in a single row although sometimes the row is slightly irregular, all combs with several curved setulae beneath them, larger smooth tapered macrochaetae distally at or past the level of the two more distal combs. — Metasternum ( Fig. 192 ) of similar length to prosternum except wider (L/ W 0.81 –0.87), apically rounded, with marginal setae and cilia along distal third of lateral margins and 3+3 (occasionally 2+3) combs of 3–10 pectinate macrochaetae.

Legs quite long, tibia L/W ratio of PI 2.6, PII 2.7–3.1, PIII 3.0–3.5; tarsi L/W ratio PI 7.6–7.7, PII range 8.0–8.4, PIII 10.6–11.0. PI ( Fig. 190 ) with a comb of four pectinate and smooth macrochaetae laterally on the distal margin of the precoxa. Coxa with scales and a group of about 12–16 macrochaetae on the anterolateral corners usually arranged in 2–3 irregular rows, followed by a field of strong pectinate macrochaetae along the external margin about 2–4 macrochaetae wide, the margin with curved slightly pectinate macrochaetae, the macrochaetae behind the margin pectinate; inner margin with 4–6 lightly pectinate macrochaetae and several smooth and delicately pectinate setae of varying thickness distally over the articulation. Trochanter with several setae, some quite strong. Femur posteriorly with some long thin pectinate macrochaetae as well as ten carrot-shaped pectinate macrochaetae along the posterior margin and a line of smooth setae posteriorly, dorsal margin with at least three short curved pectinate macrochaetae over the articulation. Tibia of PI with five stout carrot-shaped strongly pectinate macrochaetae along the ventral margin as well as several longer thinner smooth setae and an additional carrot-shaped pectinate macrochaeta on the distal end rather than the normal strong setae; anterior margin with one pectinate macrochaeta and stronger setae near the distal margin, 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. Pretarsus with two long curved lateral claws and a shorter curved medial empodial claw. PII ( Fig. 191 ) and PIII ( Fig. 192 ) similar to PI except the antero-lateral groups of macrochaetae on the coxa absent; legs progressively longer from PI to PIII (L tibia PI/PIII 0.57–0.61, L tarsus PI/PIII 0.58–0.66 and the relative length of the basal tarsal article is progressively longer, being about 0.63 of the total length on PIII.

Abdomen: Urotergite I with 1+1 lateral combs of 5–6 macrochaetae each associated with a cilium at both ends, one marginal seta and some setulae between the comb and the margin, urotergites II–VII ( Fig. 193 ) with 3+3 combs of macrochaetae as in Table 12; the lateral combs with two cilia as well as 1–3 small marginal setae and several setulae, the sublateral combs with a cilium at the mediad end as well as 1–2 marginal setae and several setulae, the submedial combs with a cilium at the laterad end as well as 2–3 marginal setae and several setulae; urotergite VIII with 2+2 combs (lacking the sublateral) also with a cilium at each end of both combs with 1–3 marginal setae and some setulae; urotergite IX glabrous. — Urotergite X ( Fig. 194 ) equilateral triangle (58–62°) in both sexes, wider at base than long (L/ W 0.68 –0.72) with many pectinate tapered setae along entire margin, and 4–5 combs of 1–5 macrochaetae per comb on each side as well as a few setulae posterior to each comb, most combs with a cilium at the mediad end.

Urosternites I and II glabrous, urosternites III–VII with 1+1 lateral combs of 15–24 pectinate macrochaetae ( Fig. 195 ) each with a few marginal setae and many setulae between the comb and the margin as well as a cilium at the laterad end. The distance between the lateral combs 1.9–3.1 times the average width of these combs, the ratio being largest on urosternite III and decreasing posteriorly.

Genital region of ♀ as in Figures 196 and 197 . Two pairs of styli, those on IX long and slender with robust setae apically and along the length of the stylus, styli of VIII ( Fig. 196 ) similar and not much smaller (0.8). Coxites VIII with long combs of 15–22 macrochaetae and just a few marginal setae and several setulae between the comb and the margin, the coxites with straight truncate posterior margin and a slightly obtuse angle (97–102°) with the inner margin, the corner being moderately rounded the curve occupying only ⅛ to ¼ the length of the posterior margin. Each coxite IX with long internal process which is very broad, being about 2.9–3.3 times longer than wide at its base and 5.3–6.4 times longer than the short pointed external process, however these inner processes are much wider along their length beyond the stylus insertion being 1.5 times wider at their widest point than at their base, the inner processes not quite reaching the apex of the ovipositor and bearing 4–5 combs of 1–5 macrochaetae along the inner margin, outer process with a few stout setae along the outer margin; inner process with numerous, quite long, closely packed setae along the expanded outer margin adjacent to the stylus, a long smooth macrochaetae inserted mediad of the base of the stylus, the inner margin with 4–5 combs of 1–5 pectinate macrochaetae. Stylus IX with several long (half the length of the stylus) pectinate macrochaetae raised perpendicular to the style axis on the posterior face. — Ovipositor of secondary type 1.56 HW, only just surpassing the apex of the internal processes of coxites IX, both pairs of gonapophyses consisting of longer basal divisions becoming progressively shorter distally except for the last divisions which are about as long as the previous two together, 13–15 divisions in total; the apical ten divisions armed with modified spines or conules which become more numerous distally, the last divisions with 7–10 modified spines; all divisions also with short fine trichobothria-like setae.

Cerci ( Fig. 198 ) first division with two incomplete rings of fine setae and trichobothria, second division with sub-basal semi ring of a few setae, those on the outside large, and a subapical ring of setae, trichobothrium and some pectinate macrochaeta externally; third and fourth divisions with two rings, the basal of trichobothria and scales the subapical of trichobothria, setae and macrochaetae; fifth and sixth intervals with sub-basal ring of setae, trichobothria and scales, a medial ring of scales and a small trichobothrium, the subapical ring of macrochaetae, setae, and cilia; seventh division with four rings, the basal and penultimate with trichobothria and scales, the second of setae and trichobothria and the ultimate as in the previous division. — Median dorsal appendage ( Fig. 198 ), first division with three rings of fine setae, following division with a basal ring of fine setae a medial ring of scales and a subdistal ring of fine setae, those on the outer sides longer; third division with two rings the basal of small setae and scales, the subdistal similar to the previous; divisions 4–6 with three rings, the basal and penultimate of scales and trichobothria, the second of setae and smaller macrochaetae, the subapical as in the previous division.

Male: Similar to female except urosternite VIII entire with posterior margin between the combs very slightly concave, almost straight. Coxites IX in ♂ separated ( Fig. 199 ) with internal process broad and shorter than that of the female being only 1.4–1.5 times longer than wide at its base and 2.4–3.3 times longer than the short pointed external process, the inner processes not quite reaching to half the length of the stylus; outer process with stout setae along the outer margin; inner process with setae along both margins, and four submarginal combs of 1–5 macrochaetae along the inner margin, as well as a long smooth macrochaetae inserted mediad of the base of the stylus. Penis typical with numerous glandular setae apically, each set on a protuberance. Parameres absent.

Habitat. This species was collected in dry leaf litter.

Etymology. The species is named obscura from a Latin word for dark to reflect the sudden darkening of the cuticle that occurs as soon as the specimens are dropped into alcohol.

Figures

Figure 176. Known distribution of Acrotelsella obscura sp. nov.

Figure 177. Acrotelsella obscura sp. nov., 10 km south of Coen, Queensland.

Figures 178–186. Acrotelsella obscura sp. nov. holotype ♀ (178) long pectinate periocular macrochaeta; (179) curved slightly pectinate marginal macrochaeta of metanotum; (180) long strongly pectinate macrochaeta of PIII; (181) darker dorsal scale of mesonotum; (182) head (cross-hatched area obscured by eye pigment); (183) antenna, scape, pedicel and basal intervals of flagellum; (184) idem, most distal surviving complete interval; (185) maxilla; (186) labium. Arrows indicate the position of the basiconic sensilla. Scale bars = 0.1 mm.

Figures 187–190. Acrotelsella obscura sp. nov. holotype ♀ (187) pronotum; (188) mesonotum; (189) metanotum; (190) presternum, prothoracic sternum and PI. Scale bars = 0.1 mm.

Figures 191–192. Acrotelsella obscura sp. nov. holotype ♀ (191) mesothoracic sternum and PII; (192) metathoracic sternum and PIII, NB spur of tibia not normally developed on this leg. Scale bars = 0.1 mm.

Figures 193–197. Acrotelsella obscura sp. nov. holotype ♀ (193) right combs of urotergite VI; (194) urotergite X; (195) right side of urosternite V; (196) right coxite VIII; (197) left coxites VII and IX with ovipositor. Scale bars = 0.1 mm.

Figures 198–199. Acrotelsella obscura sp. nov.holotype ♀ unless otherwise indicated by specimen number (198) base of cerci and medial filament (K.541677); (199) coxites IX and penis of ♂ (T259430). Scale bars = 0.1 mm.