Heterolepisma milledgei, Smith & Mitchell, 2019
Smith, Graeme B. & Mitchell, Andrew, 2019, Species of Heterolepismatinae (Zygentoma: Lepismatidae) Found on some Remote Eastern Australian Islands, Records of the Australian Museum 71 (4), pp. 139-181 : 151-158
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Heterolepisma milledgei sp. nov.
Holotype. ♂ ( HW 1.43 ) ( AM K.541007 K.541008 on two slides) LORD HOWE ISLAND: Stevens Reserve 31.52°S 159.07°E 15m asl, 25.ii.2001, Graham Milledge GoogleMaps . Paratypes. 1♂ ( HW 1.25 ) (K. 377823 in alcohol) same data as holotype GoogleMaps ; 1♀ ( HW 1.03 ) (K.261088 K.261089 on two slides) LORD HOWE ISLAND: eastern slope of Phillip Point (north head) 31.522°S 159.041°E, 1.xii.2000, CBCR Australian Museum GoogleMaps ; 1♀ ( HW 1.18 ) (K.261256 K.261257 on two slides) LORD HOWE ISLAND: Blackburn Island 31.534°S 159.060°E, 18.ii.2017, C. Reid GoogleMaps ; 1♂ ( HW 1.25 ) (K.541013 K.541014 on two slides) LORD HOWE ISLAND: Junction of Kim’s Lookout trail and North Beach trail 31.519°S 159.050°E, 18–27.ii.2001, LHIS010 /04 GoogleMaps ; 1♀ ( HW 1.10 ) (K.377863 (shared) in alcohol) LORD HOWE ISLAND: Western slope of Malabar Ridge S. of Kims Trail, 31.516°S 159.059°E, 24 November 2000, LHIS007 /L GoogleMaps ; 1 juvenile ( HW 0.75) (K.377863 (shared) in alcohol) same data as previous GoogleMaps ; 1 juvenile ( HW 0.73) (K. 377864 in alcohol) LORD HOWE ISLAND: Eastern slope of Dawson’s Point ridge near top, 31.516°S 159.049°E, 24.xi.2000, LHIS008 L GoogleMaps ; 1♀ ( HW 1.28 ) (K. 377866 in alcohol) LORD HOWE ISLAND: Western slope of Dawson’s Point Ridge, off North Beach trail, 31.083°S 159.048°E, 24.xi–1.xii.2000, LHIS12 /03 GoogleMaps ; 1 partial specimen ( HW 1.18 ) (K.377867 (shared) in alcohol) LORD HOWE ISLAND: Junction of Kim’s Lookout trail and North Beach trail, S31.519° E159.050°, 18–27.ii.2001, LHIS010 /02, (head, thorax and abdominal segments I– III) GoogleMaps ; 1 partial specimen ( HW 0.93) (K.377867 (shared) in alcohol) same data as previous, (head, thorax and abdominal segments I–V) GoogleMaps ; 1♂ ( HW 0.95) K.261258 on one slide) LORD HOWE ISLAND: Balls Pyramid , base of “Pillars of Porteus” 31.757°S 159.255°E, 26.iii.2017, F. Koehler (specimen probably subadult as styli VIII are only about half the expected size) GoogleMaps ; 1 juvenile ♂ ( HW 0.68) (K.261349 on one slide) LORD HOWE ISLAND: Balls Pyramid , rock platform at southern tip “Base Camp” 31.7575°S 159.2550°E, 26.iii.2017, F. Koehler GoogleMaps ; 1 juvenile ♂ ( HW 0.73) (K. 377869 in 100% ethanol), same data as previous GoogleMaps ; 1 juvenile ♀ ( HW 0.70) (K. 377827 in 80% ethanol) same data as previous GoogleMaps ; 1 juvenile ( HW 0.63) (K. 377870 in 100% ethanol) same data as previous GoogleMaps .
Diagnosis. This species can be distinguished from most other described species of Heterolepisma by a combination of features including the presence of macrochaetae along the anterior margin of the frons, the absence of a medial comb on urosternite I, the presence of only 1+1 macrochaetae on urosternites II–VIII and the number of styli (three pairs in the ♀ and two pairs in the ♂). It differs from the closely related H. sclerophyllum species group most obviously in the shorter urotergite X (L/W at its base of 0.36–0.47 vs 0.43–0.73) and its truncate trapezoidal shape (versus rounded).
Appearance: Medium sized silverfish ( Fig. 42 View Figures 42–50 ), thorax about 15% wider than abdomen which only tapers slightly posteriorly from about the fifth abdominal segment; appearance when live unknown.
Body length: H+B 10.1 mm; HW 1.43 mm; thorax: length up to 3.2 mm or 0.31 H+B (range 0.29–0.32); width up to 2.13 mm with no great difference in length or width between the nota although the mesonotum is the widest and the pronotum the narrowest; antennae not complete> 5.2 mm or>0.54 H+B; terminal filaments all damaged,>4.0 mm or>0.43 H+B.
Pigmentation: Pigment brownish, quite variable between specimens, with the specimen from Blackburn Island being much darker than the holotype, while others show intermediate levels of pigmentation, the variability perhaps due to the maturity of the specimen and the duration in alcohol. Flagellum of antennae evenly pale becoming slightly darker distally; pedicel and scape without pigment. Terminal filaments annulated darker brown with only the most distal part of each major division from just below the rosette of major macrochaetae to the suture with the next division devoid of pigment. Head with very small area of pigment around eyes only. Clypeus, labrum and mandibles without pigment. Maxillary palp without pigment except for slightly shaded penultimate article. Labium and labial palp largely without pigment except for small amount along the outer margin of the penultimate article. Legs without pigment except for dorsal face of the tibia and the first tarsal article of PIII where light pigment is fairly evenly distributed and a small amount on the tibia distally of PII. Urotergite X with light pigment, darkest proximally and becoming lighter distally. Coxites IX around stylus insertion and both pair of styli with very dark pigment in one specimen (K.541014), only styli IX pigmented in another specimen (K.541014), weaker in the holotype and almost absent in K. 261258. Ovipositor without pigment.
Macrochaetae: Typical for the Heterolepismatinae , smooth, hyaline or slightly straw coloured, apically bifurcate with truncated tips to each bifurcation. Some macrochaetae on tibia, stout carrot-shaped.
Scales: Quite broad, hyaline or with ribs browner distally, with numerous subparallel ribs that do not surpass the margin of the scale ( Fig. 43 View Figures 42–50 ). Scales found on top of head, absent from clypeus and labrum as well as all cephalic appendages; present on all nota, all thoracic sterna, and coxae of legs but
absent from remaining leg articles, present on all urotergites and urosternites, absent from styli and terminal filaments. Lanceolate scales not seen.
Head: Wider than long ( Fig. 44 View Figures 42–50 ). Frons with complete row of strong macrochaetae along the anterior margin which join laterally with the rows of macrochaetae along the lateral margins, running back towards and above the eyes, these rows quite dense about 2–4 macrochaetae wide, periantennal groups of about six macrochaetae and smaller setae, contiguous with the lateral marginal row. Clypeus with 1+1 long rows of macrochaetae (ca. seven or more in adult specimens) proximally and another transverse row of thinner but still well-developed setae a little distal of the middle, two of these setae on each side are long, trichobothria-like; area between these two rows well populated with setae, many of which are quite long. Labrum with transverse proximal band of cilia followed by a band of setae in proximal half, distal half with the usual row of six fine setae. — Antennae with scape longer than pedicel ( Fig. 45 View Figures 42–50 ), each with a subapical rosette of small macrochaetae and setae, as well as some cilia; ventral and lateral faces of scape, and to a lesser extent also the pedicel, with many setae and some cilia. First annulus or interval of flagellum with a subapical rosette of a few setae; subsequent six annuli with a single rosette of small setae, trichobothria and some cilia, the sutures between the annuli difficult to see in the holotype, eighth to tenth intervals divided into two annuli, each with a rosette similar to the previous, eleventh and twelfth intervals divided into two annuli but the apical annulus has two rosettes, following interval still divided into two annuli but each has two rosettes, the most distal surviving interval in the holotype (probably about mid-antenna) with four annuli per interval, each with two rosettes, the trichobothria restricted to the most distal rosette, in paratype K. 261256 the antenna is much more intact (three quarters?), each apical interval is divided into eight annuli with trichobothria still restricted to the most distal annulus, with a small basiconic sensillum (type B) at least on the fourth annulus of each interval and possibly also on the most distal annulus, as well as two basiconic sensilla type C, one on the second and the other on the fourth annulus ( Fig. 46 View Figures 42–50 ). — Mandibles ( Figs 47, 48 View Figures 42–50 ) typical for Heterolepismatinae with well-developed molar and incisor areas, a group of about 7–15 short apically bifurcated setae distally adjacent to the molar region and a bush of about 50–60 long macrochaetae externally. — Maxilla ( Fig. 49 View Figures 42–50 ) with three thick apically bifurcate macrochaetae externally proximal to the palp; lacinia short and wide, with three strong teeth, one set further back than the other two, followed by about seven lamellate processes and a row of 7–11 setae, galea with 0–5 stronger setae proximally but otherwise with only short fine cilia or setulae; apical article of maxillary palp 4.6 times longer than wide (range 4.3–4.7) and 1.3 times longer than the penultimate article (range 1.1–1.5), the ultimate article with three branched papillae, those in the male larger and more elaborate than those in the female; all articles of palp covered with fine setae, penultimate article with a few somewhat stronger setae subapically, first, second and third articles with incomplete subapical rosettes of stronger setae. — Labium ( Fig. 50 View Figures 42–50 ) wider than long, postmentum with several quite strong setae in each posterolateral corner, quite long simple setae in band about two wide across the anterior quarter, prementum with transverse and oblique groups of strong often slightly apically bifurcate setae and with short setulae distally; apical article of labial palp, 1.2 times longer than wide (range L/ W 1.1 –1.3) with five papillae arranged in a cluster arrangement with the three larger papillae in a curved line around the posterior two smaller papillae; outer margin with at least two basiconic sensilla (one type C, one type B); penultimate article with three stronger setae medially, second article with several stronger setae on the inner face and subdistally, basal article with several short strong setae in an oblique line on the anterior face.
Thorax: Pronotum ( Fig. 51 View Figures 51–59 ) with well-developed setal collar about three or four macrochaetae wide and some long cilia scattered throughout collar; chaetotaxy of lateral margins largely lost, consisting of many marginal setae or macrochaetae as well as several submarginal macrochaetae and long cilia. Anterior trichobothrium a little further than halfway along the margin and occasionally associated with a marginal macrochaeta but more often not, otherwise without any special chaetotaxy other than sometimes a couple of setulae ( Fig. 52, 54 View Figures 51–59 ). The posterior trichobothrium mediad of two submarginal macrochaetae with some two or three setulae and long cilia ( Fig. 53, 54 View Figures 51–59 ). Posterior margin with 1+1 submedian combs of two macrochaetae each associated with one or two setulae perhaps two cilia or setulae anterior to the comb ( Fig. 55 View Figures 51–59 ). — Mesonotum ( Fig. 56 View Figures 51–59 ) with similar lateral chaetotaxy to pronotum except two or three of the submarginal macrochaetae are arranged as combs of two macrochaetae; both trichobothrial areas are more posterior ( Fig. 57 View Figures 51–59 ), the anterior trichobothrium about 80% along the margin and located between a macrochaeta and the margin and the posterior area as in the pronotum, in one example (right side only of K. 261088) there are two macrochaetae mediad of the trichobothrium; 2+2 posterior macrochaetae as in pronotum. — Metanotum ( Figs 58, 59 View Figures 51–59 ) similar to mesonotum.
Presternum narrow, with transverse band of strong mostly apically bifurcate macrochaetae one or two wide plus small setae and cilia ( Fig. 60 View Figures 60–64 ). All thoracic sterna with hyaline scales. — Prothoracic sternum ( Figs 60, 61 View Figures 60–64 ) cordiform, about as long as wide at base (L/W range 0.84–1.05), posterior two fifths of lateral margins with long thin setae and cilia, 1+1 quite variable combs of 2–9 macrochaetae subparallel to the margin subdistally. — Mesosternum ( Fig. 62 View Figures 60–64 ) semi-elliptical, a little longer than wide (range L/ W 1.02 –1.15) with 1+1 subdistal combs of five, six or seven macrochaetae as well as several marginal setae, cilia and setulae. — Metasternum ( Fig. 63 View Figures 60–64 ) apically rounded or straight for a distance between the combs, wider than long (range L/ W 0.73 –0.76) with 1+1 subapical combs, each of 3–7 macrochaetae, the lateral margins adjacent to each comb with setae, cilia and setulae, the gap between the combs about four times the average width of the combs (range 2.8–4.9).
Legs ( Figs 60, 62, 64 View Figures 60–64 ) becoming progressively longer and more slender (mean tibia length PII/PI 1.3 (range 1.23–1.31), PIII/PI 1.70 (range 1.63–1.75), mean tarsus length PII/PI 1.1 (range 1.00–1.25), PIII/PI 1.50 (range 1.37–1.55), tibia L/W ratio of legs PI 3.1 (range 2.5–3.6), PII 3.6 (range 3.5–3.7), PIII 4.0 (range 3.8–4.2); tarsi L/W ratio PI 6.2 (range 6.1–6.3), PII 6.3 (range 5.9–6.8), PIII 9.2 (range 8.5– 9.8). Precoxa of PI with comb of about six macrochaetae. Coxa of PI with combs of one or two macrochaetae in the anterolateral corner, many scattered macrochaetae as well as some cilia and setulae along the outer margin, becoming more numerous distally; inner margin with seven macrochaetae distally over the articulation and another one or two strong macrochaetae subdistally, as well as a seta subdistally and a long thin seta on the dorsal face. Trochanter with several long setae, three or four thicker than the rest. Femur ventrally with several strong macrochaetae along the posterior margin and two subdistally over the articulation, numerous thin setae, some quite long scattered over the ventral and dorsal surfaces. Tibia with a strong carrot-shaped macrochaeta distally as long as apical spur and another two subequally spaced along the ventral margin, as well as several longer macrochaetae along the entire length of the ventral margin, dorsal or outer margin with one short pointed macrochaeta or two macrochaetae just distad of the middle and another subdistally; surface covered in long fine setae; apical spur bearing several small setae. Tarsi of four articles, the basal tarsal article about as long as the following articles together on PI, PII and PIII; all articles bearing numerous long thin setae, including longer stronger setae on the ventral surfaces, suture between third and fourth articles weak. Pretarsus with two long curved lateral claws and a straight medial claw. PII and PIII similar to PI.
Abdomen: Urotergite I with 2+2 combs, the lateral combs of 2–3 macrochaetae each associated with 1–2 cilia, two marginal setae and two setulae, the sublateral combs of two macrochaetae each associated with 1–2 cilia, a marginal seta and a setula ( Fig. 65 View Figures 65–76 ); urotergites II–VII with 3+3 combs, the number of macrochaetae per comb is shown in table 5, each lateral comb associated with one to four cilia, two marginal setae and sometimes a setula ( Figs 66–70 View Figures 65–76 ); urotergite VIII with 2+2 combs, lacking the sublateral comb (only one large seta in submedial comb on urosternite VIII in specimen K.541014); urotergite IX without combs but with 0–2 cilia and 2–4 small marginal setae or setulae in each infralateral corner ( Fig. 71 View Figures 65–76 ). Urotergite X ( Fig. 72 View Figures 65–76 ) short, trapezoidal (L/ W 0.39, range 0.36–0.47) with glabrous posterior margin between one or two submarginal macrochaetae in the posterolateral corners, lateral margins with several macrochaetae, setae and some cilia along entire length.
Urosternite I glabrous; urosternites II–VII with 1+1 macrochaetae each associated with a cilium laterad of the insertion, a small seta and one or two setulae between the macrochaeta and the margin ( Figs 73, 74 View Figures 65–76 ) (macrochaeta missing on one side of urosternite VII in K.541014 but cilium and seta still present); urosternite VII in female with straight posterior margin and a macrochaeta mediad of each stylus insertion and a cilium laterad of the stylus insertion, and two or three setulae on each side; urosternite VIII in the male entire ( Fig. 75 View Figures 65–76 ), its posterior margin slightly convex, its chaetotaxy similar to urosternite VII in the female ( Fig. 76 View Figures 65–76 ). Three pairs of styli in the females VII–IX ( Fig. 77 View Figures 77–85 ) and two in the male (VIII–IX).
Coxites IX of ♂ with acute inner process about 1.2 times longer than wide at its base (range 1.11–1.24) and about 2.8 times longer than the external process (range 2.63–3.31) reaching to just under half the length of the stylus, both inner and outer processes with several macrochaetae/setae along their margins emerging from both the dorsal and ventral surfaces of the processes close to or on the margin. Parameres ( Figs 78, 79 View Figures 77–85 ) a little longer than wide, with about twenty fine setae and some cilia. Penis typical for genus with numerous glandular setae apically, each set on a protuberance.
Coxite IX of ♀ ( Fig. 80 View Figures 77–85 ), the internal process acute apically, about twice as long as the external process and 1.3 times as long as broad at its base, not reaching to half the length of the stylus; external and internal margins of internal process and external margin and apex of outer process with many moderately strong setae directed both up and down. — Ovipositor ( Fig. 80 View Figures 77–85 ), very long and thin (up to 2.1 HW), surpassing the apex of stylus IX by about the length of the stylus (excluding terminal macrochaetae), composed of 39–42 divisions. Distal divisions of gonapophyses VIII and IX with only short fine setae and setulae ( Figs 81, 82 View Figures 77–85 ).
Cerci ( Figs 83, 84 View Figures 77–85 ) with five basal divisions short with no more than a single rosette of setae and trichobothria, sixth and seventh divisions each with two rosettes of setae, cilia and trichobothria and macrochaetae in the apical rosette of the seventh, subsequent divisions with three then four rosettes with macrochaetae confined to the most apical division, eight rosettes per divisions from about the thirteenth, the divisions progressively longer; most apical surviving division (about 16th in holotype) with ten rosettes per division. — Median dorsal appendage ( Figs 83, 85 View Figures 77–85 ) with glabrous first division, the following division either has two rosettes or the suture between the rosettes is too faint to see, the following two divisions with a single rosette of setae and trichobothria, the next two divisions with two rosettes and the following divisions with four rosettes; most apical surviving division (about 16th in holotype) with ten rosettes per division ( Fig. 85 View Figures 77–85 ).
Balls Pyramid variant: Both Balls Pyramid specimens dissected and mounted had only one macrochaeta in each submedial comb of the urotergites. While the possibility that this is due to their small size cannot be excluded (HW <1.03), this seems unlikely as the submedial combs of the nota in both specimens have two macrochaetae. It would appear that this could represent a morphological difference between the populations on Lord Howe Island and Balls Pyramid suggesting a fairly long period of separation. Both populations however shared identical 28S sequences and are therefore considered here as belonging to a single species (see discussion below).
Juvenile stages: In the small juvenile ♂ (K.261349) from Balls Pyramid there were no combs of two macrochaetae on the lateral margins of the meso- and metanota and only one pair of styli were developed. These observations are consistent with growth characteristics of the genus.
Habitat. Specimens were reported as collected by fogging a Banyan Fig, in leaf litter in closed rainforest ( Drypetes / Cryptocarya ) or ( Cleistocalyx / Chionanthus ), from litter in broad megaphyllous closed sclerophyll forest- ( Howea belmoryana habitat), under rocks/logs, beating Lagunaria / Cassinia , and in a pitfall trap. This suggests it dwells in leaf litter accumulations, probably in areas either protected from rain or which dry out quickly, as is the case with H. sclerophyllum ). Heterolepisma howense on the other hand seems to live under bark or within other cavities on trees. A similar separation of species has been seen by the first author on the Australian mainland where H. sclerophyllum is almost always collected from leaf litter accumulations and only rarely from the bark of trees while a sympatric undescribed species in the H. highlandi group was only ever taken from bark.
Etymology. Named for the collector of the type specimen Dr Graham Milledge, an arachnologist at the AMS.
This new species is closely related to H. sclerophyllum . Comparison of morphometric data failed to find a character (other than the L/W ratio of urotergite X) that clearly separated H. milledgei sp. nov. from H. sclerophyllum . It is possible that a difference exists in the number of ovipositor divisions (for most genotypes except that of the Megalong genotype) and the ratio of stylus VIII/IX, however data for H. milledgei sp. nov. is limited. There also appears to be a difference in the width of the gap between the combs on the metathoracic sternite (3.16–4.92 vs 1.66–3.72) except for the Glenbrook genotype (2.38–4.11). Heterolepisma milledgei sp. nov. also appears to have denser setae but an objective measure that encompasses the range of instars and the quality of preservation is currently lacking. The very limited data available suggest that there are fewer setulae in the trichobothrial areas but the number of setulae in the sclerophyllum complex needs to be re-examined.
Molecular data presented in Smith et al., 2019 found that distances of 0.9–1.8% or greater in 28S, and 7.2–14% in COI were associated with morphologically distinct species. We were able to obtain similar molecular data ( Fig. 3 View Figure 3 ) for three specimens here considered to belong to H. milledgei sp. nov., a subadult male and a juvenile from Balls Pyramid and a female from Blackburn Island (a small atoll within the main Lagoon of Lord Howe Island). The distance between H. milledgei sp. nov. and H. sclerophyllum for the 28S gene was 1.3% and 18.4–25.2% for COI. We consider this degree of difference, associated with a consistent morphological difference (trapezoidal urotergite X) as sufficient for H. milledgei sp. nov. to be considered as a species distinct from H. sclerophyllum . While distances of 6.9–8.1% were found for the COI gene between the Balls Pyramid and Blackburn Island specimens, as well as a difference in the number of macrochaetae in the submedial combs on the abdominal tergites, the two populations had identical 28S sequences. We therefore consider them to belong to the same species, but the differences in morphology and COI sequences suggest that these two populations have been isolated from each other for some considerable time and that they derived from a progenitor near to or the same as H. sclerophyllum from the eastern coast of mainland Australia.
Smith (2014) mentioned a specimen of H. howense from Lord Howe Island (K. 261088 K. 261089) that he compared to the newly described H. sclerophyllum . Hardly considering that there could be two species of Heterolepisma on Lord Howe Island he believed, due to the arrangement of styli and the shape of urotergite X, that the specimen belonged to the inadequately described H. howense , however, the redescription of H. howense above, now makes it clear that this specimen is not H. howense but belongs to H. milledgei sp. nov..
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