Acrotelsella arboricola, 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 : 37-44

Acrotelsella arboricola sp. nov.

urn:lsid:zoobank.org:act:4E409D40-84D5-4EBD-B3F0-75BE3A20C554

Figs 103–127

Holotype ♀ (HW 1.35) QUEENSLAND: Undara , rocks above camp 18.2049°S 144.5706°E 789m asl, 5.viii.2013, Graeme Smith & Louise Smith, pyrethrum bark spray to square pattern bark eucalypt or bloodwood, QM T259424 (on two slides) . Paratypes (one male, three females, five juveniles) 1♂ (HW 1.30), same data as holotype, QM T259431 (on two slides) ; 2♀♀ (HW 1.09, 104) same data as holotype, AMS K.377989 (in alcohol) ; 1♀ (HW 1.45) Undara, rocks above camp 18.2049°S 144.5706°E 790m asl, 5.viii.2013, Graeme Smith & Louise Smith, pyrethrum spray to dead barkless tree, AMS K.541678 (on two slides); 5 juveniles (HW 0.80, 0.45, 0.45, 0.43, 0.43) same data as previous, AMS K.378026 (in alcohol). Localities shown on the map in Figure. 103 .

Diagnosis. This species can be distinguished from other described Acrotelsella with a simple ovipositor and trapezoidal thoracic sterna by a combination of characters including the presence of five papillae on the labial palp (versus three or four) combined with the distinct annulations on the flagellum and terminal filaments. It also has fewer combs on each side of the prothoracic sternum (4–5 versus 5–8) and the presence of some irregularly aligned (not all simply linear) combs on the thoracic sterna. It also differs from the nearest species ( A. marginata sp. nov.) by the smaller number of thick carrot-shaped macrochaetae on the tibia of PI (one versus three) with these macrochaetae being present but much thinner. When live this species lacks the lighter margins seen in Acrotelsella marginata sp. nov.

Description

Appearance: Medium size silverfish with narrow body, thorax not much wider than the abdomen which only tapers slightly posteriorly. Scale pattern in alcohol mottled brown, when live mottled dark grey or black with lighter areas around the posterior combs of the nota, without lighter bands along sides of nota ( Fig. 104 ).

Body length: H+B up to 9.8 mm, HW 1.5 mm; thorax: length 3.0 mm or 0.28–0.33 H+B; width 2.4 mm with the mesonotum being slightly wider than the pronotum and metanotum, the metanotum being slightly shorter than the pro- and mesonota. Antennae incomplete, maximum preserved length 8.3 mm or>0.68 H+B; terminal filaments all broken, maximum length of terminal filaments 9.0 mm or about H+B length.

Pigmentation: Light to dark brown. Flagellum of antennae with distinct annulations, the lighter areas restricted to the distal two or three annuli of each interval; pedicel with some patches of strong dark pigment most prominent on the outer dorsal face, scape usually without obvious pigment. Frons with pigment around the eyes and among the macrochaetae anterior to the eyes, clypeus and labrum, mandibles with pigment among bushes of macrochaetae, last three articles of maxillary palp with medium pigment in the proximal half to two thirds, slightly lighter in third article; labial palp with rich brown pigment along the outer margins proximally, penultimate article with brown pigment along the entire outer margin. Nota and thoracic sterna without obvious pigment. Coxae of legs with only slight pigment in the anterior outer corners. Trochanter with a distinct patch on the distal posterior margin. Femora with very dark almost black pigment on most of the posterior margin predominantly in the area distad of the bulge and also distally on the dorsal margin. Tibia with dark patches on dorsal face, especially distally but also proximally. First tarsal article with pigment, remaining articles without pigment. Abdominal segments without obvious pigment except for moderate dark pigment on coxites IX and its inner processes. Urotergite X darker laterally at base only. Ovipositor with some pigment overall. Cerci and median filament generally with distinct annulations with the lighter region restricted to the last annulus of each division. Abdominal styli with moderate pigment evenly distributed over whole length.

Macrochaetae: Variable, pectinate or smooth brown to hyaline, the pectinations are quite strong distally but can be very subtle in other parts of the shaft ( Figs 105–106 ).

Scales: Variable in shape, with numerous sub-parallel ribs that do not surpass the margin of the scale ( Fig. 107 ), those dorsal are brown in alcohol, those ventral hyaline. Scales found on top of head and clypeus, on scape, on second and third articles of maxillary palp, on mentum of labium, all nota, all thoracic sterna, legs (except for trochanter and apical three articles of tarsi), all urotergites and urosternites, styli and terminal filaments.

Head: ( Fig. 108 ) wider than long, with 1+1 open bushes of macrochaetae aligned in several subparallel rows on the antero-lateral corners. Eyes dark brown in alcohol preserved material. The row of macrochaetae extends along the lateral margin with a small gap above the antennal bases behind which is another row of macrochaetae two or three macrochaetae wide which extends to and in front of the eyes; the peri-antennal group is strong with an isolated macrochaeta between the group and the marginal rows. Clypeus with 1+1 very dense bushes of strongly pectinate macrochaetae as well as 2+2 macrochaetae between these bushes and the frons plus a few setae laterally. Labrum also with 1+1 bushes of pectinate macrochaetae as well as many small simple setae, some longer than others. — Antennae fairly long, scape ( Fig. 109 ) quite long with scales over surface and a preapical ring of numerous strong pectinate setae; pedicel with preapical ring of strong simple setae and cilia as well as smaller setae on the dorsal face as well as some small scattered setulae over face forming a circle; basal nine annuli/intervals of flagellum short, gradually increasing in length distally, each with a ring of setae, cilia and trichobothria; tenth interval with two annuli, the trichobothria restricted to the distal annulus; twelfth interval with three annuli, fourteenth with four annuli. In the most distal surviving intervals (about ¾ length) there are two very similar chains to each interval with three annuli each with rings of simple setae and cilia as illustrated in Figure 110 , with type B basiconic sensilla present but not abundant. — Mandibles 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 about 90 pectinate macrochaetae externally as well as scattered simple setae. — Maxilla ( Fig. 111 ) with two delicately pectinate macrochaetae, a seta and a cilium externally proximal to the palp, the lacinia with three strong teeth, one set further back than the other two, followed by six lamellate processes and a row of eight smooth apically bifurcate setae, galea a little longer than the lacinia with several small setulae or cilia over the surface and 4–5 larger setae basally; maxillary palp of moderate to short length, apical article 5.0–6.0 times longer than wide and 1.1–1.2 times as long as the penultimate article which is a little shorter than the third and longest article, the ultimate article with probably with a basiconic sensillum (type B) however it appeared differently on other specimens and could even be a circular sensillum; last two articles of palp with fine setae only, second and third article with scales and thin setae, some of which are a little stronger near the distal end of the article, first article with an incomplete subapical ring of slightly thicker setae. — Labium ( Fig. 112 ) short and broad, postmentum with transverse row of strong mostly simple setae, prementum with transverse and oblique rows of short strong simple or apically truncate setae, apically with curved setulae; penultimate article of labial palp with two strong setae medially; apical article subrectangular slightly expanded medially, about as long as wide, only a little eccentric in shape (L/ W 0.85 –0.91) with row of five papillae of compact type and a basiconic sensillum type B near the outer margin at the level of the papillae, surface covered with numerous fine setae.

Thorax: Pronotum ( Fig. 113 ) with setal collar about one to two macrochaetae wide towards the mid region but only a single macrochaeta wide towards the margins; lateral margins with many reasonably strong pectinate setae along the margin, with 8–9 combs of 1–3 strongly pectinate macrochaetae along each margin. Two open trichobothrial areas, the anterior trichobothrial area about 0.41 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 (on specimen K.541678 there is a clear developmental anomaly on one side with two combs missing between anterior and posterior trichobothrial two macrochaetae (sometimes one) with the trichobothrium areas resulting in a more posterior position on this side and at the mediad end and a cilium at the laterad end, most combs the appearance of being associated with N-1); posterior associated with 1–3 setulae posterior to the comb. Posterior trichobothrial area is located about 0.76–0.77 of the distance margin of all nota with 1+1 combs of 5–7 insertion points, along the margin (0.81 in the anomalous specimen) and is each associated with a few small setae between the comb and associated with the last comb which is usually composed of the margin and a cilium at each end; the outermost insertion on the comb is occupied by a long thin trichobothrium-like seta. The distance between the lateral combs of the pronotum 44% the total width of the pronotum. — Mesonotum ( Fig. 114 ) with lateral chaetotaxy similar to pronotum but with ten combs each of 1–3 macrochaetae, the anterior trichobothrial area located 0.64–0.68 along the lateral margin associated with comb N-2 composed of a single macrochaeta with the trichobothrium located between the macrochaeta and the margin, with a few setulae posterior to the comb and a cilium at the mediad end. Posterior trichobothrial area slightly more posterior than that on the pronotum (0.77–0.87) the trichobothrium located mediad to the comb of a single macrochaeta and with a few setulae posterior to the comb. — Metanotum ( Fig. 115 ) similar to mesonotum with 8–9 combs of 1–4 macrochaetae, the anterior trichobothrial area associated with comb N-1 of one macrochaeta 0.77–0.80 along the margin, the posterior trichobothrial area associated with the most posterior comb (0.86–0.90 along margin).

Presternum with transverse row of mostly pectinate setae ( Fig. 116 ). — Prothoracic sternum ( Fig. 116 ) large and trapezoidal 0.93–0.96 times as long as wide at its base, antero-lateral corners with several setae on the margin, posterior ⅔ of lateral margins with fringe of setae and some cilia as well as 4–5 combs each composed of 1–6 pectinate macrochaetae arranged in single straight or irregular combs, also with 1+1 larger submarginal setae distally. — Mesosternum ( Fig. 117 ) trapezoidal, 1.1–1.2 times as long as the prosternum but similar in shape, about a long as wide at its base (L/ W 0.89 –0.92) with two setae in the anterolateral corners and long thin simple marginal setae and cilia at the posterior corners which do not extend much beyond the combs, 1+2 or 2+2 combs distally of 2–5 macrochaetae with additional slightly submarginal 1+1 setae nearer to the posterior end; all combs associated with 0–1 setulae. — Metasternum ( Fig. 118 ) trapezoidal, shorter and wider than the mesosternum (L/ W 0.71 –0.75) with a few fine setae in the anterolateral corners, with marginal setae and cilia only along margins adjacent to the combs; with 1+1 or 1+2 subdistal combs of 2–7 pectinate macrochaetae.

Legs of average dimensions, tibia L/W ratio of PI 2.4–2.9, PII 3.2–3.6, PIII 3.5–4.7; tarsi L/W ratio PI 5.5–7.0, PII 7.6–8.2, PIII 9.6–10.5. PI ( Fig. 116 ) with a row of four pectinate macrochaetae laterally in pigmented region on the precoxa. Coxa with scales and a group of about nine macrochaetae on the anterolateral corners followed by a field of pectinate macrochaetae along the external margin about three macrochaetae wide; inner margin with a four 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 insertions along the mediad margin. Trochanter with a few strong smooth setae and a thin pectinate macrochaeta. Femur posteriorly with several slender pectinate macrochaetae, in addition to many smooth setae along the margin to the posterior bulge then a row of about ten setae in a well delineated darkly pigmented region along the margin to the articulation; anterior edge without strong macrochaeta along most of the margin except for two pectinate macrochaetae inserted well before the articulation. Tibia of PI with only one stout carrot-shaped pectinate macrochaetae near the end of the posterior margin and two more slender tapered pectinate macrochaetae along the posterior margin, as well as several longer thinner setae; anterior margin with two macrochaetae insertions as well some subdistal setae over the articulation; apex of tibia with the usual apical spur which is covered in several setae. Tarsi with four articles, the basal article of PI less than 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, those ventrally near the apex distinctly stronger than the others. Setae of tibia and tarsi quite long and strong as well as numerous. Pretarsus with two long curved lateral claws and a shorter curved medial empodial claw. PII ( Fig. 117 ) and PIII ( Fig. 118 ) similar to PI except the macrochaetae laterally on the coxae are absent from the anterior quarter; tibia of PII and PIII have more pectinate carrot-shaped macrochaetae, tibia of PIII probably with a long trichobothria-like seta about ⅓ the distance along the outer margin adjacent to a pectinate macrochaeta (two insertions seen but setae lost); 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 6–7 macrochaetae, urotergites II–VII ( Fig. 119 ) with 3+3 combs of 4–11 macrochaetae as in Table 9, urotergite VIII with 2+2 combs (lacking the sublateral), urotergite IX glabrous; all combs with a cilium at each end and with a few small setae and setulae between the comb and the margin. — Urotergite X ( Fig. 120 ) of female narrow triangular (46° in female) but with the apex sometimes slightly withdrawn from the apex of a triangle (but on the anomalous K.541678 the apex is distinctly round as in Figure 121 ), slightly wider at base than long (L/ W 0.78) with many setae along entire margin and 4–5 combs on each side, the combs composed of 1–6 macrochaetae per comb usually with a cilium at the mediad end of each comb, as well as a few setulae posterior to each comb. Urotergite X in male ( Fig. 122 ) distinctly less acute (65°) than in female (L/W at base 0.57).

Urosternite I and II glabrous, urosternites III–VII with 1+1 lateral combs of 7–14 pectinate macrochaetae ( Fig. 123 ) each with a smaller 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 4.5–15.1 times the average width of these combs, the ratio being largest on urosternite III and decreasing posteriorly.

Genital region of ♀ as in Figure 124 . 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 9–14 macrochaetae and a smaller number of thin setae and setulae between the comb and the margin, the coxites with rounded inner corners, the straight section being about ½–⅔ the width of the distal margin. Coxites IX with long rounded internal process about 4.5–5.2 times longer than wide at its base and 8.3–14.3 times longer than the short pointed external process, the inner processes greatly surpassing the apex of styli IX including macrochaetae; outer process with several setae externally, inner process with strong smooth macrochaetae along the inner margins and pectinate macrochaetae on the outer margin where many large scales also exist. — Ovipositor of primary type with rows of fine setae subapically on each article, quite long 2.0 HW, reaching beyond 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, 25–29 divisions in total.

Cerci ( Fig. 125 ) first division almost glabrous with just a couple of minute setae near the lateral margin, following two divisions each with a single rings of setae and trichobothria, the following division difficult to discern suture with next division, probably also a single ring of setae, cilia and trichobothria, the division merging with the following division which has two rings, the basal of trichobothria and scales, the distal with setae, cilia, trichobothria and macrochaetae, the following division similar with two rings, the next division with three rings, the basal of setae trichobothria and probably scales, the middle of scales and trichobothria, the distal as previous, the following division with four rings, the basal of scales, the second of setae and trichobothria, the third of scales and the distal as previous. — Median dorsal appendage ( Figs 125–126 ) with similar arrangement of increasing length as well as number and structure of divisions. Most distal surviving divisions difficult to examine due to pigmentation, with about 11 annuli, the seventh and eighth also with several trichobothria and cilia; there appear to be some basiconic sensilla type B and possibly also a circular sensillum but this may be an artefact. Epiproct and paraprocts very darkly sclerotized.

Urosternite VIII in ♂ entire with 1+1 combs of nine macrochaetae as well as some thin marginal setae and setulae, posterior margin between the styli almost straight. Coxites IX in ♂ separated ( Fig. 127 ) each side with a macrochaeta mediad to the base of the stylus. The internal process very acute apically about 3.0–3.3 times longer than the external process and 1.3–1.4 times as long as broad at its base. External and internal margins of internal process and external margin of outer process with many moderately strong setae and macrochaetae. 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. This species as collected from the bark of both living and dead trees.

Etymology. This species is named arboricola , from the Latin word for trees, referring to its habitat of living within and under the bark of trees

Figures

Figure 103. Known distribution of Acrotelsella arboricola sp. nov.

Figure 104. Acrotelsella arboricola from Undara, Queensland.

Figures 105–112. Acrotelsella arboricola sp. nov. holotype ♀ (105) long pectinate macrochaeta of frons; (106) highly pectinate, carrotshaped macrochaeta of tibia of PII; (107) darker dorsal scale of metanotum; (108) head (cross-hatched area obscured by eye pigment); (109) antenna, scape, pedicel and basal intervals of flagellum; (110) idem, most distal surviving complete interval; (111) maxilla; (112) labium. Scale bars = 0.1 mm.

Figures 113–116. Acrotelsella arboricola sp. nov. holotype ♀ (113) pronotum; (114) mesonotum; (115) metanotum; (116) presternum, prothoracic sternum and PI. Scale bars = 0.1 mm.

Figures 117–118. Acrotelsella arboricola sp. nov. holotype ♀ (117) mesothoracic sternum and PII; (118) metathoracic sternum and PIII. Scale bars = 0.1 mm.

Figures 119–124. Acrotelsella arboricola sp. nov. holotype ♀ unless otherwise indicated by specimen number; (119) combs of left side of urotergite V; (120) urotergite X; (121) aberrant urotergite X (K.541678); (122) urotergite X of ♂ (T259431); (123) urosternite V; (124) coxites VIII and IX with ovipositor. Scale bars = 0.1 mm.

Figures 125–127. Acrotelsella arboricola sp. nov. holotype ♀ unless otherwise indicated by specimen number (125) base of cerci and medial filament; (126) median dorsal filament, most distal surviving division (T259431); (127) coxites IX and penis of ♂ (T259431). Scale bars = 0.1 mm.