Hypsibius heardensis, Miller & Mcinnes & Bergstrom, 2005

Miller, William R., Mcinnes, Sandra J. & Bergstrom, Dana M., 2005, Tardigrades of the Australian Antarctic: Hypsibius heardensis (Eutardigrada: Hypsibiidae: dujardini group) a new species from sub-Antarctic Heard Island, Zootaxa 1022 (1), pp. 57-64 : 59-63

Hypsibius heardensis sp. nov. ( Figures 2A–E)

Diagnosis. Medium sized, pale Hypsibius with smooth cuticle. Average buccal tube width ending in oval pharynx with large apophyses, two macroplacoids, and very small septulum. External claws with large accessory points, cuticular bars present at the base of all internal claws.

Holotype. ( Fig. 2A): Sex undet. 7 January 1988. Coll. D. Bergstrom. Deposited at The Australian National Insect Collection, CSIRO Division of Entomology , Canberra, ACT, Australia ( ANIC).

Type Locality: Three sites in the vicinity of Red Island (52º 58’S, 73º 18’E) ( Fig.1B), a promontory off Laurens Peninsula on the northwest end of Heard Island, including lava field immediately south of lagoon, east of alluvial flats at 50 m a.s.l. Sample from lava substrate that was extremely craggy with numerous loose boulders, occasional patches of Azorella selago Hook. f. ( Apiaceae ). Quadrat sampled a shallow bryophyte layer of predominantly Sanionia uncinata (Hedw.) Loeske. The site was very free draining and moist, receiving wind­driven mist.

Paratypes. Data same as for holotype; eight individuals collected at the same locality. Paratypes are also deposited in ANIC, the British Antarctic Survey Data Resource Centre, and the Academy of Natural Sciences, Philadelphia .

Etymology. The species is named in honour of the beautiful and remote Heard Island. Description. Body slender, length 350.0 m (200.0–382.0 m) ( Fig. 2A). Eyes absent. Mouth sub­terminal. Cuticle smooth. Buccal tube 24.0 m (18.0–26.0 m) long and 2.0 ìm (1.7–3.0 m) wide with one bend in posterior portion ( Figs 2C, 3B). In lateral view the margins of the apophyses for the insertion of the stylet muscles are in the form of “semi­lunular hooks”. Stylet supports are attached near middle of buccal tube 15.0 m (10.0–16.0 m), giving a stylet supports to buccal tube pt ratio of 62.5 % (56–63 %). Pharynx slightly oval with large apophyses 2.5 m (1.5–3.0 m), two rod­shaped, elongated macroplacoids, of which the first is slightly constricted in the middle, 5.5 m (4.0–6.0 m), and is marginally longer than second, 4.5 m (3.0–5.0 m). Microplacoids absent but a small septulum is present (1.0 by 0.5 ìm) ( Figs 2B–C, 3A–B).

Claws of legs IV slightly larger than claws of legs I–III ( Figs. 2D–E, 3C–D). On leg IV the external claws have a short basal part 5.0 m (3.0–7.0 m), a long primary branch, giving a total claw length of 16 m (11.0–19.0 m), with a short smooth secondary branch. The internal claws on leg IV are shorter, 7.0 m (7.0–13.0 m), and broader. Accessory points are present on the primary branches of both claws. The base of internal claw of leg IV is extended and curved upward at ends. Light transmitting areas are visible on both claws. A heavy cuticular bar 2.0 x 8.0 m (2.0–9.0 m), which is smooth on top and ragged below, extends from base of the inner claws of legs I–III in most specimens ( Figs. 2D–E, 3C). However, the bars are sometimes poorly sclerotized and lacking on legs I. A thin, 5.0 m long (3.0–6.0 m), cuticular bar is present between bases of claws of leg IV.

The eggs are smooth shelled and 2–5 were observed laid inside the exuvium.

Distribution. Known so far only from Heard Island and Macquarie Island.

Comments. Hypsibius heardensis sp. nov. belongs to a group of Hypsibius species referred to as the dujardini group, which exhibit a colourless, smooth cuticle, and an oval pharynx with two rod­shaped macroplacoids. Other members of this group include H. allisoni Horning, Schuster, & Grigarick, 1978 , with a type locality in New Zealand and distribution including South America and Antarctica, H. convergens ( Urbanowicz, 1925) , a species complex of cosmopolitan distribution, H. dujardini ( Doyère, 1840) , with a mainly Northern Hemisphere distribution, H. pachyunguis Maucci, 1996 , from Greenland and H. pedrotti Bertolani, Manicardi & Gibertoni, 1987 from Italy (see McInnes, 1994). Details of the comparative morphology of the dujardini group are tabulated in Table 1.

In addition to the differences in physical characters, H. dujardini is described as hygrophilous or hydrophilous, having been reported from aquatic and wet terrestrial habitats (e.g., Argue 1974; Petersen 1951; Ramazzotti & Maucci 1983; Bertolani 1982, Bertolani et al. 1987). H. heardensis was collected from a range of habitats from discontinuous bryophyte dominated vegetation, which while not dry was never water­logged, to a continually ‘wet’ site bordering a meltwater lake. This indicates a marginally more eurytropic preference than H. dujardini . Of those species that have, or include, Southern Hemisphere distributions, H. allisoni (a possible synonym of H. convergens ( Ramazzotti & Maucci, 1983)) , was originally found in a eurytropic habitat of lawn moss in New Zealand ( Horning et al. 1978), and H. convergens in the Southern Hemisphere has most commonly been described from the more eurytropic to xerotrophic habitats of epiphytic or epilithic mosses and lichens (e.g., Horning et al. 1978).

Though superficially similar, H. heardensis can also be differentiated from Acutuncus antarcticus ( Richters, 1904) by the mouth, buccal structure and claws typical of the genus Hypsibius . The elliptical structures surrounding the mouth, the shape and armature of the buccal cavity, along with the dissimilar claws and free laid, sculptured eggs which led Pilato & Binda (1997) to erect a new genus Acutuncus for the species A. antarcticus , are not found in H. heardensis .

­ No data

The current authors have previously commented on the inconsistencies between animals found in the sub­Antarctic and maritime Antarctic in comparison with the published descriptions of Hypsibius dujardini , inserting “cf” into some references (e.g., McInnes 1995). Specimens of H. cf. dujardini collected from the maritime Antarctic and from sub­ Antarctic South Georgia, though similar to H. heardensis , have eyespots, and differ in the type and form of the cuticular bars and claws on the legs. The description of this maritime Antarctic/ South Georgia species will be discussed in a later paper.

Miller et al. (2001) listed Hypsibius sp. from Macquarie Island and following reexamination this has been confirmed as H. heardensis . Thus the current distribution for H. heardensis encompasses the type locality, Heard Island, in the South Indian Province and Macquarie Island, in the South Pacific Province (see Smith 1984).