Acrotelsella albicaudata, 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 : 166-173

Acrotelsella albicaudata sp. nov.

urn:lsid:zoobank.org:pub:C36AD292-6727-45DD-8F28-9C078FE72E67

Figs 35–66

Holotype ♂ ( HW 1.13 ) VICTORIA: Murray-Sunset N.P. 34.73984°S 142.01870°E 111m asl, 25.ix.2013, Graeme Smith, leaf litter under Acacia sp. , NMV T-22586 (on two slides) . Paratypes 1♀ ( HW 1.08 ) same data as holotype, NMV T-22587 (on two slides) ; 1 juvenile ( HW 0.78) same data as holotype, AMS K.261327 (on two slides) ; 1♂ ( HW 1.40 ) VIC: Murray-Sunset N.P. Pioneer track 35.03444°S 141.73926°E 52m asl, 26.ix.2013, Graeme Smith, Eucalyptus leaf litter on top of ridge, AMS K.377968 (in alcohol, about to moult) .

Diagnosis. In the field, this species can easily be distinguished from other described Acrotelsella by the very white tail filaments. Additional characters differentiating the species include the presence of only a single pair of styli in both sexes, seven papillae on the last article of the labial palp, the secondary type ovipositor and the short internal processes of coxites IX of the female which lack transverse combs.

Description

Appearance: Medium-sized silverfish, with thorax a bit wider than the abdomen which tapers posteriorly. Scale pattern as in Figure 36 , in alcohol mottled brown with some dorsal scales much darker than others. Eyes dark brown. Antennae with darker annulations, terminal filaments extraordinarily white.

Body length: Up to H+B 8.6 mm, HW 1.38 mm; thorax: length 2.6 mm or 0.30–0.32 H+B; width 2.25 mm with the pronotum being slightly narrower than the mesonotum, the mesonotum slightly wider than the metanotum, all nota of about the same length; antennae incomplete, maximum preserved length 4.2 mm or>0.5 H+B; terminal filaments all broken, maximum length of cercus 2.9 mm or>0.46 H+B; median dorsal appendage maximum preserved length 3.4 mm (>0.54 H+B), but not very long.

Pigmentation: Flagellum of antennae with distinct annulations; pedicel with very distinct dark ring at its apex. Frons with darker pigment along the sides of the head and through the anterior bushes, labrum and clypeus without pigment. Mandibles and maxillae without pigment among bushes of macrochaetae, ultimate article of maxillary palp with reddish brown pigment in the medial third and only light pigment in the other two thirds, penultimate article with dark pigment in the distal half, third article with dark pigment in distal third, second article with dark pigment in distal third and lighter pigment proximally. Labial palp with quite dark pigment on much of the apical and subapical articles with dark pigment distally on the second article, basal article with very little pigment. Nota and thoracic sterna without obvious pigment. Precoxa of legs very darkly pigmented. Coxae with quite dark pigment in the anterior “shoulders: extending down the outer margin among the bristles. Trochanter with darker more reddish pigment along posterior margin especially distally. Femora with dark reddish pigment along most of the posterior margin, especially distally and also on anterior margin distally, the density of the pigment along the posterior margin as well as on subsequent leg articles makes it difficult to discern sockets of setae and perhaps even macrochaetae. Tibia with dark pigment around all of distal margin. First tarsal article dark distally, remaining legs articles without pigment.Abdominal segments without obvious pigment dorsally, ventrally the posterior urosternites and coxites pigmented, especially coxites IX around the stylus insertion. Ovipositor without pigment. Cerci and median filament very white. Abdominal styli with moderate pigment.

Macrochaetae: Variable, pectinate or smooth ( Figs 37–39 ), quite dark to straw coloured.

Scales: Of quite variable shape with numerous sub-parallel ribs that do not or only slightly surpass the margin of the scale ( Fig. 40 ), the number of ribs and degree of pigmentation varies considerably across the nota but no scales with wide spacings observed. Both ventral and dorsal surfaces with scales with pigmented ribs although this is generally less on the ventral surface; scales of legs can be quite dark. Scales found on top of head, on scape and pedicel, on mandibles, 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, medial filament and cerci, those on the terminal filaments hyaline.

Head: ( Fig. 41 ) wider than long. Frons with 1+1 not very dense bushes of macrochaetae aligned in subparallel curved rows on the antero-lateral corners separated by a medial gap. Along the margins posterior to these bushes is a very small gap in the row of macrochaetae along the margin above the antennal bases after which there is another bush of pectinate macrochaetae extending towards the barely isolated peri-antennal groups which consist of about 10 macrochaetae and a long thin trichobothrium-like seta; posterior to these the marginal macrochaetae rows extend to the eyes about two wide with about six macrochaetae above the eyes ending in a group of three or four strong macrochaetae near the posterior margin of the head; sides of head posteriorly with usual long thin trichobothrium-like seta. Clypeus with 1+1 dense bushes of about 50 slightly thinner pectinate macrochaetae as well as a few curved setae laterally. Labrum also with 1+1 dense bushes of about 35 pectinate macrochaetae; face of labrum with scattered simple curved setae and at least one longer thin apically bifurcate seta. Eyes dark chestnut brown. — Antennae probably shorter than H+B, scape ( Fig. 42 ) quite long with scales over surface and a preapical ring of numerous setae; pedicel also with scales, with preapical ring of simple setae and cilia, with a second incomplete ring of smaller setae below this and a few small additional setae on the inner face; first annulus/interval of flagellum with only a few setae in a ring with a subapical ring of simple setae; next annulus with a single ring of simple setae and two trichobothria; subsequent intervals with single ring of setae and two trichobothria with some cilia appearing by the fifth interval. Further intervals of flagellum poorly preserved on slides, becoming quite shrunken, however circular areas that may be poculiform sensilla may be present. The dark pigment also obscures observation of sensilla, but some circular and basiconic sensilla type B were seen. — Mandibles ( Fig. 43 ) typical for Acrotelsella with well-developed molar and incisor areas; a group of about seven strong apically bifurcated but simple setae distally adjacent to the pectinate molar area and a bush of about 60 pectinate macrochaetae externally as well as scattered simple setae and scales. — Maxilla ( Fig. 44 ) with two thick minutely apically bifurcated but otherwise smooth macrochaetae and a smaller apically bifurcate seta externally proximal to the palp, the lacinia with three strong teeth, one set further back than the other two, followed by 5–7 lamellate processes and a row of just 3–4 thin simple or apically slightly bifurcate setae, galea distinctly longer than lacinia with about 4–5 smooth, simple or apically bifurcate setae externally in its basal half and a few setulae or cilia distally; maxillary palp not particularly long and thin, apical article ( Fig. 45 ) 4–5 times longer than wide and a bit longer than the penultimate article (range 1.0–1.3) which is 0.7 times as long as the third and longest article, the ultimate article with at least one basiconic sensillum type B and two type C, and possibly a circular sensillum although this was very indistinct and may be an artefact, last three articles of palp with fine setae, basal article with ring of thicker setae, second article also with subapical ring of slightly thicker setae. — Labium ( Fig. 46 ) short and broad, postmentum with transverse row of simple setae, prementum with transverse and oblique rows of short strong setae, apically with long curved setulae; labial palp short, apical article subrectangular ( Fig. 47 ), about as long as wide (0.94–1.07) with seven papillae of compact type arranged in a single curved row near the outer margin, these papillae were difficult to see in the holotype and paratype NMV T-22587 due to the high degree of pigmentation in this and penultimate articles, but were clearly distinguished in the paratype K.377968; no basiconic sensilla were seen but this may also be an artefact of the pigmentation (only one ultimate article of the holotype was preserved and those of paratype NMV T-22587 were too shrivelled to examine), surface covered with numerous fine setae as well as longer fine setae.

Thorax: Pronotum ( Fig. 48 ) with setal collar about two to three macrochaetae wide plus cilia and setulae, without gap medially; lateral margins with stronger subtly pectinate as well as smaller setae and some cilia along the margin, with eight combs of 1–3 macrochaetae along each margin. Two open trichobothrial areas; the anterior trichobothrial area 0.39–0.44 along the margin and associated with comb N-3, the comb composed of only a single macrochaeta with the trichobothrium between the macrochaeta and the margin; all combs associated with a few setulae; the posterior trichobothrial area is located 0.77–0.79 along the margin and is associated with the last comb (N), this comb composed of two macrochaetae with the trichobothrium at the mediad end and a cilium at the laterad end. Posterior margin with 1+1 combs of 6–8 macrochaetae ( Fig. 49 ) associated with several setulae between the comb and the margin and a cilium at each end; the combs not widely situated with the gap between them only 43–44% of the width of the pronotum. — Mesonotum ( Fig. 50 ) with lateral chaetotaxy similar to pronotum with nine combs of 1–3 macrochaetae, the anterior trichobothrial area located 0.57–0.61 along the lateral margin associated with comb N-2 composed of two macrochaetae with the trichobothrium located between the macrochaetae and the margin, with one to three 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 (0.83–0.87 along margin), the trichobothrium located mediad to the comb of just one macrochaeta and with one to four setulae posterior to the comb. Posterior margin with quite laterad 1+1 combs of eight macrochaetae with cilia at each end and several setula or small setae between the comb and the margin. — Metanotum ( Fig. 51 ) similar to mesonotum with eight combs of one to three macrochaetae, the anterior trichobothrial area located 0.71–0.78 along the margin associated with comb N-1 of 1–2 macrochaetae, the posterior trichobothrial area associated with the most posterior comb of only one macrochaeta and the posterior 1+1 combs each of eight macrochaetae with a cilium at each end and several setulae or small setae between the comb and the margin.

Presternum narrow, with single transverse row of subtly pectinate setae ( Fig. 52 ). — Prothoracic sternum ( Fig. 52 ) 0.94 times as long as wide at its base, parabolic, slightly truncate and glabrous apically, antero-lateral corners with fields of about 6–9 large simple small setae, posterior three quarters of lateral margins with fringe of strong setae and some cilia as well as 6+6 or 6+7 combs each composed of 3–9 pectinate macrochaetae with the macrochaetae somewhat irregularly arranged. — Mesosternum ( Fig. 53 ) about as long as wide at its base (L/ W 1.02 –1.05) and a little longer than prosternum (1.2 times as long) without setae in the anterolateral corners, simple setae along the posterior quarter of the margin and 2+2 or 2+3 combs and 1+1 single pectinate macrochaetae distally, both sets of combs composed of 6–9 pectinate macrochaetae plus a few posterior setulae. — Metasternum ( Fig. 54 ) a little shorter and wider than the mesosternum (L/ W 0.82 –0.83), slightly pentangular in shape, apically glabrous with marginal setae and cilia along distal ¼ of lateral margins, with 2+2 combs of pectinate macrochaetae of 4–7 macrochaetae arranged in single but slightly irregular rows and occasionally with 1+1 single submarginal macrochaetae (absent from K.377968) more distally.

Legs fairly robust, tibia L/W ratio of legs PI 2.5 (range 2.3–2.7), PII 2.4 (range 2.2–2.7), PIII 3.4 (range 3.3–3.8); tarsi L/W ratio PI 6.3 (5.0–7.0), PII 7.1 (range 6.7–7.5), PIII 7.8 (range 7.3–8.1). PI ( Fig. 52 ) with a row of about six pectinate macrochaetae laterally on the distal margin of the precoxa. Coxa with scales and a group of about twelve macrochaetae on the anterolateral corners followed by a field of strong pectinate macrochaetae about 2–3 macrochaetae wide along the external margin; inner margin with six tapered slightly pectinate macrochaetae and three or four smooth strong setae distally over the articulation as well as some smaller setae along the distal margin. Trochanter with a single fine pectinate macrochaeta as well as several fine setae and cilia. Femur posteriorly with six (?) strong pectinate macrochaetae as well as a few small setae and cilia, in addition to three strong macrochaetae on the dorsal surface towards the distal end over the articulation. Tibia of PI with about five or six stout, carrot-shaped, pectinate macrochaetae along the ventral margin as well as three smaller macrochaetae on the dorsal margin and a few smooth setae over the articulation, the usual apical spur with only 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. Pretarsus with two long curved lateral claws and a shorter curved medial claw. PII ( Fig. 53 ) and PIII ( Fig. 54 ) similar to PI except the antero-lateral groups of macrochaetae on the coxa absent; legs progressively longer from PI to PIII (tibia PI/PIII 0.57–0.65, tarsus PI/PIII 0.69–0.75) and the relative length of the basal tarsal article is progressively longer, being about three quarters of the total length on PIII, the last two articles are quite short and the suture between them almost indistinguishable on the holotype.

Abdomen: Urotergite I with 1+1 lateral combs of 3–6 macrochaetae each associated with a cilium at either end, 2–4 small marginal setae and 2–3 setulae between the comb and the margin, urotergites II–VII ( Figs 55–58 ) with 3+3 combs of macrochaetae as in Table 4, the lateral and submedial combs each with a cilium at each end, the sublateral combs with just a single cilium at the mediad end, urotergite VIII with 2+2 combs (lacking the sublateral), urotergite IX glabrous; all combs with 1–6 small as well as 3–5 setulae between the comb and the margin. — Urotergite X ( Fig. 59 ) acutely triangular (57° in K.377968, 64° in holotype but wider 99° in K.261327 but this looks deformed and therefore probably not representative, urotergite lost during dissection of NMV T-22587), wider at base than long (L/ W 0.56) with many setae along entire margin both above and below (all lost on holotype), and 3+3 combs of three to five macrochaetae per comb (all macrochaetae lost) as well as several setulae posterior to each comb and a cilium at the mediad end.

Urosternite I and II glabrous with the posterior margin of urosternite I protruding a little in the middle, urosternites III–VII with 1+1 lateral combs of 11–16 pectinate macrochaetae ( Fig. 60 ) each with 4–6 marginal setae and a few setulae between the comb and the margin as well as a cilium at the laterad end of each comb only. The distance between the lateral combs 3.1–4.4 times the average width of these combs, the ratio being largest on urosternite IV and decreasing posteriorly. Only one pair of styli present in both sexes.

Genital region of ♀ as in Figure 61 . Styli short with robust setae apically and along the length of each stylus. Coxites VIII with long combs of 12 macrochaetae and a lesser number of setulae and marginal setae, the coxites with almost square inner corners but rounded near the angle. Coxites IX with short, wide, round internal process, about 1.5 times longer than wide at its base and only 3–4 times longer than the short pointed external process, the inner processes just reaching the apex of the ovipositor; outer process with a few setae externally, inner process with several long smooth setae along the outer margins as well as finer setae or setulae and many scales, inner margin of process with setae insertions and some small setae. — Ovipositor ( Figs 61, 62 ) short, about equal to HW, only just attaining the apex of the short internal processes of coxites IX, both pairs of gonapophyses with very long basal divisions then quite short divisions, about 15–16 divisions in total; of the secondary type, the posterior gonapophyses with three conules apically, the posterior gonapophyses with a single conule.

The contrast in pigment levels between the quite dark anal region, including the sharp horn-like paraprocts and epiproct and the unpigmented terminal filaments is quite striking. Cerci ( Figs 63, 64 ) first division with some small trichobothria and small setae, following two basal divisions much shorter than wide, each with a single ring of setae and trichobothria, divisions four and five somewhat longer but still shorter than wide with two rings, the most basal with trichobothria and probably scales and small setae, the most dorsal ring with larger setae, cilia and macrochaetae on the dorsal and outer margins, divisions six and seven longer than wide with an inconspicuous medial ring of insertions which appear to be mostly scales, the basal ring with setae, trichobothria and scales, the distal with larger setae, cilia and macrochaetae; most distal surviving divisions (thirteenth) with four subdivisions each with two annuli, each annulus with a ring of chaetotaxy, the most distal ring of large macrochaetae and cilia also with a ring of setae proximal to it; trichobothria appear restricted to the third most distal subdivision, long cilia at the distal end of the second, and third subdivisions; hyaline scales are present on these distal divisions although difficult to distinguish. — Median dorsal appendage ( Figures 63, 65 ), first division very short, glabrous, following division with two rings of fine setae and trichobothria, divisions three and four a little shorter than two, each with a single ring of fine setae and trichobothria, fifth division with two rings, the most basal with scattered trichobothria, scales and a fine seta, the most distal with trichobothria, cilia and long fine setae, division with two rings, the most basal with setae and scales, the most distal with stronger as well as some fine setae, long cilia and trichobothria, division seven with three rings, the middle one appearing to be only scales; most distal surviving divisions (about half length) formed of four annuli, each annulus with two rings of chaetotaxy; trichobothria present on the basal and third annuli, long cilia distally on the second and ultimate annulus; hyaline scales present on the basal ring of some annuli.

Coxite VIII in ♂ entire ( Fig. 66 ) with 1+1 combs of 13 macrochaetae, with a cilium at the laterad end, as well as about six marginal setae and several setulae, the posterior margin similar to other urosternites. Coxites IX in ♂ separated each side with a long smooth macrochaeta (about ¾ the length of the internal process) mediad to the base of the stylus. External and internal margins of internal process with many moderately strong setae and macrochaetae. Outer process small triangular with several stout pectinate setae along the outer margin. Penis typical with numerous glandular setae apically, each set on a protuberance. Parameres absent.

Habitat. Collected in dry leaf litter on sandy substrate.

Etymology. The species is named albicaudata for its striking white tail filaments.

Remarks

The new species has several characters which place it closer to Hemitelsella species. It has only a single pair of styli, the internal processes of coxites IX in the female are short and rounded. The processes of coxites IX however lack transverse combs and the setae of the tarsi lack the rounded tips. Furthermore, the bushes on the head are stronger than those of Hemitelsella species and more like those in Acrotelsella and the anterior trichobothrial areas of the pronotum are like Acrotelsella and associated with comb N-3 rather N-2. As mentioned above, this molecular clade including Acrotelsella , Hemitelsella and Qantelsella species needs further investigation.

Figures

Figure 35. Known distribution of Acrotelsella albicaudata sp. nov.

Figure 36. Acrotelsella albicaudata sp. nov., Murray Sunset N.P.

Figures 37–47. Acrotelsella albicaudata sp. nov.holotype ♂ (37) long pectinate supra-ocular macrochaeta; (38) distal inferior macrochaeta of tibia; (39) marginal macrochaeta of pronotum; (40) darker dorsal scale; (41) head (cross-hatched area obscured by eye pigment); (42) antenna, scape, pedicel and basal intervals of flagellum; (43) mandible; (44) maxilla; (45) idem, apex of ultimate article of palp, showing the location of the sensilla; (46) labium; (47) idem, ultimate article of palp. Scale bars = 0.1 mm.

Figures 48–53. Acrotelsella albicaudata sp. nov. holotype ♂ (48) pronotum, left half; (49) idem, right posterior comb; (50) mesonotum, left side; (51) metanotum, left side:(52) presternum, prothoracic sternum and PI; (53) mesothoracic sternum and PII.Scale bars = 0.1 mm.

Figures 54–60. Acrotelsella albicaudatasp. nov.holotype ♂ (54) metathoracic sternum and PIII; (55) urotergite V; (56) urotergite III, left lateral comb; (57) idem, left sublateral comb; (58) idem, left submedial comb; (59) urotergite X; (60) right sublateral comb of urosternite IV. Scale bars = 0.1 mm.

Figures 61–66. Acrotelsella albicaudata sp. nov. holotype ♂ unless otherwise indicated with specimen number (61) coxites VIII and IX and ovipositor of female; (62) idem, apex of gonapophyses; (63) base of cerci and medial filament; (64) cercus, most distal surviving divisions; (65) medial filament, most distal surviving division; (66) urosternite VIII and coxites IX with penis and stylus IX (NMV T-22587). Scale bars = 0.1 mm.