Isotopenola australis ( Womersley, 1934 )

Potapov, Mikhail, Babenko, Anatoly, Fjellberg, Arne & Greenslade, Penelope, 2009, Taxonomy of the Proisotoma complex. II. A revision of the genus Subisotoma and a description of Isotopenola gen. nov. (Collembola: Isotomidae), Zootaxa 2314, pp. 1-40 : 28-32

Isotopenola australis ( Womersley, 1934)

Figs 9 , 77–96 , Tab. 2

Cryptopygus australis Womersley, 1934: 87

Proisotoma (Subisotoma) australis ( Womersley, 1934) : Greenslade 1994 Material. Holotype: subadult male, Australia, Victoria, You Yang Mts (SAMA). 7 individuals, adult females and subadult males, Australia, Victoria, You Yang Mts, under Big Rock, leaf litter, 05.vii.2009, leg. P. Greenslade (SAMA and MSPU). Several tens individuals, Australia, Northern Territory, Emily Gap, Alice Springs, 03.vi.1978, old Eucalyptus , leg. A. Zakharov (SAMA and MSPU).

Redescription. Size 0.7–1.5 mm. Body shape plump, with strong cryptopygy. Colour from grey to light greyish brown, with pigment grains scattered on body. All abdominal segments clearly separated, Abd.VI small, hidden under Abd.V ( Fig. 85 ). Dorsal side of body, antennae, furca, and the most portions of legs with regular thin primary granulation. Ventral side of trunk and head, bases of legs, and intersegmental areas on lateral sides with irregular wrinkles and secondary granulation ( Fig. 84 ). Degree of granulation development varies depending on individual. Ocelli 8+8, G and H clearly smaller. PAO elliptical, wide, without constriction, about 1.4–1.9 as long as ocellus diameter and 0.8–0.9 as long as U3. Maxillary outer lobe with simple maxillary palp and with 4 sublobal chaetae. Labral formula as 2/554. Labium with all five papillae (А– Е) present, papilla E with only five guard chaetae ( Fig. 90 ). Proximal part of labium with 3 chaetae, basomedian field with 4 chaetae. Ventral side of head with 3+3 postlabial chaetae ( Fig. 83 ). Ant.1 with 2 bms, dorsal and ventral, and 2 ventral sensilla (s) ( Fig. 91 ). Ant.2 with 3 bms and 1 laterodistal s. Ant.3 without bms and with 5 distal s (four of AO and one lateral s) and without additional sensilla on its dorsal side ( Fig. 89 ). Sensilla on Ant.4 hardly differentiated, subapical organite small, microsensillum present. Ant.1 and Ant.2 with 12 and 24–27 chaetae, respectively.

Tergal sensilla conspicuous, shorter and finer than ordinary chaetae. Sensillar formulas 55/44445 (s) and 11/111 (ms) ( Figs 9 , 89–90 ). One sensillum on one side of tergite lost in some individuals (the variants 54/ 44445, 55/43345, 55/43445, 55/34445, 55/44444 were found in the population from Emily Gap). Position of macrosensilla rather stable, on Abd.I–III set well anterior to p-row. On Abd.I microsensilla anterior to and between sensilla, on Abd.II laterally to sensilla (sometimes almost at a level with them), on Abd.III very close to sensilla. All tergites with dense cover of chaetae, normal or needle-like (see sex dimorphism below). Dorsal axial chaetom of Th.II–Abd.III as 7–9,7–9/5–6,5–6,5–6. Macrochaetae hardly developed, longest chaetae on Abd.V about 0.2 times as long as this tergite length. Sternum of Th.III without chaetae ( Fig. 84 ).

Unguis with inner tooth. Unguiculus with narrow basal lamella about half as long (0.5–0.6) as U3. Ti.1–3 with a few additional chaetae, with about 21, 23, 25–27 chaetae in total, respectively. Reproductive males without modified chaetae on Ti.3. Tibiotarsal tenent chaetae 1–2– 2 in number. Ventral tube with 4+4 laterodistal and about 5–6 caudal chaetae (with 4 of which in one transversal row). Tenaculum with 4+4 teeth and one chaeta. Submedial setaceous field on sterna of Abd.III with 4–6 chaetae, anterior furcal subcoxa with 7–10, posterior one with 5–7 chaetae. Anterior side of manubrium without chaetae, posterior side with about 20–26 chaetae on the main part and usually with 4+4 chaetae on laterobasal lobes. Dens with one subapical chaeta anteriorly and 6 or (more rarely) 5 posterior chaetae, arranged as 2 or 3 basal, 2 at the middle and 1 subdistal. Mucro rather long, with two teeth, the subapical one less distinct. Ratio of manubrium: dens: mucro = 4.5–7.0: 2.9–4.4: 1 ( Figs 80 , 86 ). Each anal lobe with 3 setulae of middle size.

Sex dimorphism. Males from population from Emily Gap with more needle-like chaetae which covering almost all dorsal surface of trunk and head ( Figs 93–94, 96 ). Females with these chaetae only on Abd.IV–V ( Figs 91–92, 95 ). Subadults and juveniles have fewer ‘needles’ depending on sex and age. The needles completely absent in individuals of early instars.

Affinity. Isotopenola australis is an oligochaetotic species having only 3+3 postlabial chaetae (versus 4+4 or more in other known species of the genus), 12 chaetae on Ant.I (versus more than 16, excluding I. delicata ), and few additional chaetae on tibiotarsi (versus many chaetae in other species). Isotopenola australis is also exceptional in having well visible needle-like chaetae on body which were not mentioned by Womersley nor by Salmon in their descriptions of Australian and New Zealand species of Cryptopygus .

We studied a holotype of Cryptopygus australis Womersley, 1934 (small subadult male, Australia, Victoria, You Yang Mountains, in SAMA). Only a few characters were visible in holotype: oligochaetotic tibiotarsi, clavate tenent chaetae as common for the group (1–2–2), mucro bidentate, dens with 6 and 5 (on left and right sides) posterior and 1 anterior chaetae, 6+6 equal ocelli are visible, G and H hardly visible. The exact number of tergal macrosensilla was not possible to determine. Our description was completed with the specimens collected at the type locality (You Yang Mts.) ( Figs 77–82 ) and from arid zone of Australia (Emily Gap, Northern Territory). The latter specimens show some differences from typical populations. They are larger (up to 1.5 mm, vs. up to 1.0 in typical specimens), paler, have more chaetae on tergites (but variability of this character overlapped in these forms), and shorter sensilla on body (compare Figs 78, 79 and 87, 88 ). The sexual dimorphism described above is based on population from Emily Gap. Possibly, the similar phenomenon occurs in typical population but a reliable conclusion can not be made since we have only adult females and subadult males which both were armed as shown on Figs 91–92 . The chaetotaxy of adult males in typical I. australis is unknown.

In our material, such a relatively few number of sensilla on body is only shared with Isotopenola sp. 4 ( New Zealand, Mt. Stokes Track, leg. K. Marske, J. Allwood) which is possibly conspecific with Cryptopygus terrigenus Salmon. This species differs from I. australis at least in a less developed furca ( Fig. 116 ) and more chaetae on tibiotarsi. In samples from near Alice Springs (Kunoth Paddock, Hamilton Downs Station, West Macdonnell Ranges) another species superficially similar to I. australis was seen. In contrast to I. australis , it is characterised by multiplication of the sensillar chaetotaxy and a postlabial area with 4+4 chaetae which characters are more common for the Isotopenola species studied.

Distribution. Known only from the Victoria and Northern Territory of Australia. According to the catalogue of Australian Collembola ( Greenslade 1994) this species is widely distributed in Australia but all records need verification.

Figures

FIGURES 9 – 12. Sensillar chaetotaxy of Isotopenola: 9, Isotopenola australis (5,5 / 4,4,4,4,5); 10, Isotopenola delicata sp. nov. (sensillar polychaetosis); 11, Isotopenola loftyensis (sensillar polychaetosis); 12, Isotopenola nilgiris (4,4 / 3,3,3,3,4).

FIGURES 77 – 82. Isotopenola australis. (Australia, Victoria, You Yang Mts.): 77, ocelli, PAO, and Ant. 1; 78, Th. II; 79, Abd. V (adult female); 80, dens and mucro; 81, chaetotaxy of tibiotarsus of leg 1; 82, Ant. 1 (lectotype).

FIGURES 83 – 88. Isotopenola australis. (Australia, Northern Territory, Emily Gap): 83, postlabial chaetae (encircled); 84, ventral side of Th. III; 85, profile of three last abdominal segments; 86, ventral chaetotaxy of Abd. II – V (tenaculum not shown); 87, Th. II; 88, Abd. V, sf – II and sf – III – setaceous fields on Abd. II and III, respectively.

FIGURES 89 – 96. Isotopenola australis. (Australia, Northern Territory, Emily Gap): 89, Ant. 3, dorsal view; 90, labial palp (only e-guard chaetae are shown in details); 91 – 94, distribution of needle – chaetae on body in females (91, 92) and males (93 – 94); 95 – 96, chaetotaxy of head and two basal antennal segments in adult female (95) and adult male (96).

FIGURES 116 – 117. Isotopenola spp.: 116, Isotopenola sp. 4 (New Zealand), ventral chaetotaxy of Abd. II – IV (tenaculum not shown); 117, I. nilgiris, dens and mucro, and apical part of dens, dorsal view. sf – II and sf – III – setaceous fields on Abd. II and III, respectively.