Acrotelsella marginata, 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 : 28-34

Acrotelsella marginata sp. nov.

urn:lsid:zoobank.org:act:5BCF1182-7641-4AA9-9952-F720AFF716D1

Figs 79–100

Holotype ♀ (HW 1.44) QUEENSLAND: Jardine River NP, Jardine River South campsite 11.1399°S 142.3637°E 16m asl, 22.vii.2013, Graeme Smith, leaf litter in river edge forest (eucalypt, plus Acacia or Melaleuca ), QMT259422 (on two slides). Paratypes (four males, five females, five juveniles) 1♂ (HW 1.20) same data as holotype, QMT259429 (on two slides); 1♂ (HW 1.24) same data as holotype, AMS K.378008 (in alcohol); 1♀ (HW 1.50) Jardine River NP, Jardine River South campsite 11.1406°S 142.3626°E 15m asl, 21.vii.2013, Graeme Smith, leaf litter at base of tree, AMS K.541667 (on two slides); 1 subadult ♀ (HW 0.80) 1 juvenile ♂ (HW 0.73) same data as previous, AMS K.378009 (in alcohol); 1♀ (HW 1.25) Pennefather 12.2918°S 141.7033°E 7m asl, 19.vii.2013, Graeme Smith, paperbark leaf litter on sand, AMS K.541665 (two slides); 1♀ (HW 1.23) Pennefather 12.2916°S 141.7059°E 7m asl, 19.vii.2013, Graeme Smith, bark spray to soft bark eucalypt, AMS K.541666 (on two slides); 2♀♀ (HW 1.03, 1.00) 1♂ (HW 0.88) 3 juveniles (HW 0.73, 0.73, 0.60) same data as previous, AMS K.378010 (in alcohol); 1♂ (HW 1.18) Pennefather 12.2919°S 141.7076°E 10m asl, 19.vii.2013, Graeme Smith, abandoned termite galleries on ti tree, AMS K.378011 (in alcohol).

Not included in type series. 1♀ (HW 1.38) Wenlock River 13.1008°S 142.9406°E 133m asl, 27.vii.2013, Graeme Smith, bark spray to square bark tree, AMS K.541676 (on two slides) ; 1♂ (HW 1.29) ♀ (HW 1.05) 1 subadult ♂ (HW 0.90) same data as previous, K.378028 (in alcohol) ; 1 juvenile ♀ (HW 0.73) Wenlock River 13.1008°S 142.9409°E 128m asl, 27.vii.2013, Graeme Smith, bark spray to square bark tree, AMS K.378027 (in alcohol) ; 6 juveniles (HW 0.58, 0.55, 0.53, 0.48, 0.43, 0.43) same data as previous, AMS K.378025 (in alcohol). All localities shown on map in Figure. 79 .

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 lighter scales on the margins of the nota when live, very weak annulations of the antennae, the number of papillae on the apical article of the labial palp (five), the larger number of combs on the prothoracic sternum (5–8 versus 4–5) and the very weak or absent annulations on the terminal filaments.

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 recently moulted specimens have distinct lighter bands along sides of at least the pronotum ( Fig. 80 ) but we do not have enough photos, especially of the clade to which the holotype belongs (see comments).

Body length: H+B up to 10.6 mm, HW 1.5 mm, thorax: length 3.1 mm or 0.28–0.37 H+B, width 2.4 mm with the mesonotum being slightly wider than the pronotum and metanotum. Antennae incomplete, maximum preserved length 8.8 mm or>0.84 H+B; terminal filaments all broken, maximum length of terminal filaments 6.1 mm or>0.58 H+B.

Pigmentation: Light to dark brown. Flagellum of antennae with weak annulations, the lighter areas restricted to the distal two annuli of each interval; pedicel with variable pigment, sometimes absent but when present usually only as patch on outer face but occasionally extending as medium brown pigment over much of dorsal face, scape usually without pigment but a small patch basally on some specimens. Frons without pigment around the eyes and among the macrochaetae anterior to the eyes, labrum without pigment, clypeus sometimes with pigment patches below bushes, mandibles with pigment among bushes of macrochaetae, last three articles of maxillary palp with light to medium pigment which is lighter at each end, second article without pigment; labial palp with pigment around inner and inner basal margin of ultimate article and inner and/or outer distal margin of penultimate article, slight pigment distally on the ante-penultimate article. Nota and thoracic sterna without obvious pigment. Coxae of legs with only slight pigment in the anterior outer corners. Trochanter with some pigment along outer margin especially distally. Femora with pigment on posterior margin predominantly in the area distad of the bulge and also distally on the dorsal margin. Tibia with some pigment in the distal third especially on the dorsal margin. First tarsal article with pigment, remaining articles without pigment or with a small amount medially. Abdominal segments without obvious pigment except for light pigment on anterior outer margins of urotergite X. Ovipositor with some light pigment distally. Cerci and median filament generally with evenly distributed medium density pigment overall however the most distal two annuli may have slightly less pigment than the rest.Abdominal styli with light pigment.

Macrochaetae: Variable, pectinate or smooth straw coloured, the pectinations are generally not strong and may be very delicate on many setae and tapered macrochaetae ( Figs 81–82 ).

Scales: Variable in shape, with numerous sub-parallel ribs that do not surpass the margin of the scale ( Fig. 83 ) those dorsal are brown in alcohol, 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 apical three articles of tarsi), all urotergites and urosternites, styli and terminal filaments.

Head: ( Fig. 84 ) 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 almost connected with the lateral 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. 85 ) 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 setulae scattered 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; thirteenth interval with three annuli, fourteenth with four annuli. In the most distal surviving intervals there are two very similar chains to each interval with a total of about 20 rings of chaetotaxy per chain; with type B basiconic sensilla present but not abundant. — Mandibles typical for Acrotelsella with prominent molar and large incisor areas; a group of about eleven strong apically bifurcated but simple setae distally adjacent to the pectinate molar area and a bush of about 100 pectinate macrochaetae externally as well as scattered simple setae. — Maxilla ( Fig. 86 ) with two smooth or delicately pectinate macrochaetae, two setae and a cilium externally proximal to the palp, the lacinia with three strong teeth, one set further back than the other two, followed by seven lamellate processes and a row of six 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 long and thin, apical article 4.6–6.8 times longer than wide and 0.97–1.14 times as long as the penultimate article which is a little shorter than the third and longest article, the ultimate article with basiconic sensilla (type B); 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. 87 ) 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; second article of labial palp with two strong setae medially, apical article quite variable in shape, usually expanded medially about as long as wide and eccentric in shape (L/ W 0.81 –1.35) with single row of five papillae of compact type (only four on one side of the holotype) 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. 88 ) with setal collar about 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 and 8–9 combs of 1–3 strongly pectinate macrochaetae. Two open trichobothrial areas; the anterior trichobothrial area about 0.37–0.41 of the distance along the margin associated with comb N-3, the trichobothrium almost always being placed between the single macrochaeta of the comb and a larger slightly submarginal macrochaeta; posterior trichobothrial area is located about 0.75–0.77 along the margin and is associated with the last comb which is usually composed of a single macrochaeta (rarely two) with the trichobothrium at the mediad end and a cilium at the laterad end, most combs associated with 1–4 setulae posterior to the comb. Posterior margin of all nota with 1+1 combs of 5–7 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 distance between the lateral combs of the pronotum 38–44% the total width of the pronotum. — Mesonotum ( Fig. 89 ) with lateral chaetotaxy similar to pronotum but with 10–12 combs each of 1–4 macrochaetae, the anterior trichobothrial area located 0.62–0.65 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 (0.84–0.88), the trichobothrium located mediad to the comb of a single macrochaeta with a few setulae posterior to the comb. — Metanotum ( Fig. 90 ) similar to mesonotum with 9–10 combs of 1–4 macrochaetae, the anterior trichobothrial area associated with comb N-1 of one macrochaeta about 0.73–0.75 along the margin, the posterior trichobothrial area associated with the most posterior comb (0.85–0.87 along margin).

Presternum with transverse row of small setae ( Fig. 91 ). — Prothoracic sternum ( Fig. 91 ) large and trapezoidal 0.94–1.05 times as long as wide at its base, antero-lateral corners with several simple setae all on the margin, posterior ¾ of lateral margins with fringe of fine setae and some cilia as well as 5–8 combs each composed of 1–7 pectinate macrochaetae arranged in single straight or curved combs, sometimes a bit complex with some macrochaetae offset from the main row, also with 1+1 larger submarginal setae distally. — Mesosternum ( Fig. 92 ) trapezoidal a little larger than prosternum (1.11–1.25 times as long) but similar in shape, about as long as wide at its base (L/ W 0.95 –1.05) with a few fine setae in the anterolateral corners and with long thin simple marginal setae and cilia at the posterior corners not extending much beyond the combs and 2+2 combs (rarely 2+3) distally of 2–5 macrochaetae without additional slightly submarginal 1+1 strong setae nearer to the posterior end; all combs associated with 0–1 setulae. — Metasternum ( Fig. 93 ) trapezoidal, shorter and wider than the mesosternum (L/ W 0.72 –0.81) with a few fine setae in the anterolateral corners, with marginal setae and cilia only along margins adjacent to the combs; with 1+1 (rarely 1+2) subdistal combs of 4–10 pectinate macrochaetae.

Legs of average dimensions, neither long and slender nor short and stout, tibia L/W ratio of PI 2.2–2.7, PII 2.2–3.2, PIII 3.3–3.9; tarsi L/W ratio PI 6.0–7.5, PII 6.1–8.9, PIII 9.1–10.9. PI ( Fig. 91 ) with a row of several 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 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 robust smooth setae along the margin to the posterior bulge then a row of about 13 setae along the margin to the articulation; anterior edge without strong macrochaetae along the margin and at least two pectinate macrochaetae over the articulation. Tibia of PI with three stout carrot-shaped pectinate macrochaetae along the posterior margin as well as several longer thinner delicately pectinate or smooth setae and a row of shorter stout setae near the distal margin; anterior margin with one pectinate macrochaeta as well 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, 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. 92 ) and PIII ( Fig. 93 ) similar to PI except the macrochaetae laterally on the coxae are reduced in the anterior half; the tibia of PIII appears to have more pectinate carrot-shaped macrochaetae than the other legs, tibia of PIII with a long trichobothria-like seta about ⅓ the distance along the outer margin adjacent to a pectinate macrochaeta; 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 5–6 macrochaetae, urotergites II–VII ( Fig. 94 ) with 3+3 combs of 0–11 macrochaetae as in Table 6, urotergite VIII with 2+2 combs (lacking the sublateral), urotergite IX glabrous; the lateral and submedial combs with a cilium at each end and the sublateral with a cilium only at the mediad end; all combs with several small setae and setulae between the comb and the margin. — Urotergite X ( Fig. 95 ) of female narrow triangular (42–52°) but with the apex sometimes slightly withdrawn from the apex of a triangle, slightly wider at base than long (L/ W 0.74 –0.89) with many setae along entire margin and 5–6 combs on each side, the combs composed of 1–5 macrochaetae usually with a cilium at the mediad end as well as a few setulae posterior to each comb. Urotergite X in male less acute (57°) than in female.

Urosternite I and II glabrous, urosternites III–VII with 1+1 lateral combs of 7–14 pectinate macrochaetae ( Fig. 96 ) 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 3.8–13.0 times the average width of these combs, the ratio being largest on urosternite III and decreasing posteriorly.

Genital region of ♀ as in Figure 97 . 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 11–13 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 ⅓–⅔ the width of the distal margin. Coxites IX with long rounded internal process about 4.2–5.6 times longer than wide at its base (longer in larger specimens) and 7.5–14.0 times longer than the short pointed external process, the inner processes surpassing the apex of styli IX including macrochaetae; outer process with several setae externally, inner process with strong smooth macrochaetae along the margins, being very dense 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 1.5–1.9 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, 24–27 divisions in total.

Cerci ( Figs 99–100 ) first division almost glabrous with just a couple of minute setae near the lateral margin; following division with two rings of setae and trichobothria, the following division with five rings the basal, middle and distal with setae and trichobothria, the second and fourth with small trichobothria and scales; following division with only two rings, the basal of scales setae and trichobothria, pectinate macrochaetae and cilia appearing in the most distal ring; the fifth division with three rings, the basal two of scales and trichobothria; the next two divisions with four rings, the basal and third of scales and trichobothria; following divisions with increasing number of rings. — Median dorsal appendage ( Fig. 99 ) with similar arrangement of increasing length as well as number and structure of divisions. Most distal surviving division with 13 annuli, the sixth and seventh predominantly of trichobothria and cilia. Epiproct and paraprocts very darkly sclerotized.

Urosternite VIII in ♂ entire with 1+1 combs of 11–13 macrochaetae as well as some thin marginal setae and setulae, posterior margin between the styli slightly concave. Coxites IX in ♂ separated ( Fig. 100 ) each side with a macrochaeta mediad to the base of the stylus. The internal process very acute apically about 3.7–4.0 times longer than the external process and 1.6–1.7 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 pectinate setae along the outer margin. Penis typical with numerous glandular setae apically each set on a protuberance. Parameres absent.

Habitat. This species was collected by spraying the bark of various tree species, from leaf litter and from abandoned termite galleries.

Etymology. The species is named marginata from the Latin noun for margin, referring to the lighter margins of the pronotum.

Comment. The material collected at Wenlock River was excluded from the type series because of insufficient molecular data and its geographic distance from the remainder of the specimens, however the morphology conforms to A. marginata sp. nov.

Molecular data also suggested that there are two clades very close to A. marginata sp. nov. that differ from each other in COI by 1.8-5.1% and within group variation of up to 5.1%. It was more difficult to find morphological differences between these clades. All have light markings on the edge of the nota but in one clade this appears to be limited to the pronotum ( Fig. 80 ), however we only have a photo of a single specimen from this clade, and its scale covering is not in good condition. The other two clades have distinct light margins along all nota as well as urotergite X ( Figs 101–102 ). Specimens belonging to the first clade (which includes the type specimens of A. marginata sp. nov.) were mostly collected in leaf litter although twice while spraying the bark of a tree, the other two clades were only collected by spraying bark. The first clade also has the urosternal combs closer together than on the other two clades with the gap between the combs relative to the average length of the comb being 3.8–13.0 (with the length of the gap greater for the anterior combs than the posterior combs) compared to 3.9–20.8 with the difference being most obvious on the anterior segments (compare Tables 6, 7 and 8). The combs of the prothoracic sternum of the first clade are sometimes irregular but in the other two clades all macrochaetae were arranged in simple rows. In the first clade, the anterior trichobothrium of the pronotum is almost always located between a macrochaeta on the margin and a macrochaeta mediad of the trichobothrium, whereas in the other two clades there was no incidence observed where a marginal macrochaeta is aligned with this comb and trichobothrium. Within the two latter clades A. aff. marginata F2 appears to have a smaller gap between the most posterior combs (segments VII and VIII) of 3.9–4.8 while A. aff. marginata F3 has a gap of>6.0. There is significant overlap in the geographic distribution of all three clades with two specimens from different clades being collected within a few hundred metres of each other but in different habitats. We are therefore uncertain about the significance of these differences and have chosen to describe only one of these clades as a species but record the other two clades as A. aff. marginata F2 and F3. However, we accept the possibility that these clades do represent distinct species and that more convincing morphological differences may eventually be found, perhaps by more detailed studies of scale morphology or the arrangement of various sensilla. It may even be possible to separate the clades solely on the basis of the scale pattern of living specimens, however more material in good condition would need to be photographed.

Figures

Figure 79. Known distribution of Acrotelsella marginata sp. nov. (circle) and two closely related taxa A. aff. marginata F2. (square) and A. aff. marginata F3. (inverted triangle).

Figure 80. Acrotelsella marginata sp. nov. from Pennefather, Queensland.

Figures 81–87. Acrotelsella marginata sp. nov. holotype ♀ (81) long pectinate macrochaeta of frons; (82) finely pectinate macrochaeta of coxa of PI; (83) darker dorsal scale of pronotum; (84) head, cross-hatched area obscured by eye pigment; (85) antenna, scape, pedicel and basal intervals of flagellum; (86) maxilla and palp, arrow showing location of basiconic sensillum; (87) labium, chaetotaxy omitted from left palp. Scale bars = 0.1 mm.

Figures 88–91. Acrotelsella marginata sp. nov. holotype ♀ (88) pronotum, left half; (89) mesonotum, left side; (90) metanotum, left side; (91) part of presternum, prothoracic sternum and PI. Scale bars = 0.1 mm.

Figures 92–94. Acrotelsella marginata sp. nov. holotype ♀ (92) mesothoracic sternum and PII; (93) metathoracic sternum and PIII; (94) urotergite V, right side combs. Scale bars = 0.1 mm.

Figures 95–97. Acrotelsella marginata sp. nov. holotype ♀ (95) urotergite X; (96) urosternite VII, posterior margin; (97) right coxites VIII and IX with ovipositor. Scale bars = 0.1 mm.

Figures 98–100. Acrotelsella marginata sp. nov. holotype ♀ unless otherwise indicated by specimen number (98) base of cerci and medial filament; (99) most distal surviving division of cercus; (100) left coxite IX and penis of male (QMT259429). Scale bars = 0.1 mm.

Figure 101. Acrotelsella aff. marginata F2 from Punsand Bay campground, Queensland.

Figure 102. Acrotelsella aff. marginata F3 from Captain Billy Road, Queensland.