Exogoninae Langerhans, 1879
Genus Exogone Örsted, 1845
Exogone heterosetoides australis Hartmann-Schröder & Rosenfeldt, 1988
Vouchers. VINSON WEST: station 1MFB (best condition) and station 38MFB (all antennae missing) NIMROD: station N12FB (lateral antennae missing), INFLEX: 1MFA (median antenna missing).
Diagnosis. Vouchers to some extent damaged, with only voucher VINSON WEST, station 1MFB in good condition; the following diagnosis based on this specimen. Complete specimen; very small, fragile, slender species; 4mm long, 0.2 mm wide for 39 chaetigers. Integument smooth; colour in alcohol pale yellow.
Prostomium about twice as wide as long bearing three antennae and two palps. Palps about as long as prostomium; fused throughout their length. Antennae smooth, arising nearly at same level, positioned anterior to eyes; lateral antennae short, spindle-shaped; median antenna longest, about three times the length of the lateral ones, cirriform. Two pairs of distinct red eyes present, positioned close together, anterior pair large, cup-shaped, posterior pair smaller, spherical. Pharyngeal tube extending through 2 chaetigers, proventricle extending through chaetigers 3-5. First segment achaetous laterally with a pair of smooth, very short, rounded tentacular cirri.
Parapodia uniramous, short but distinct. Dorsal cirri missing on chaetiger 2, otherwise present, smooth ovoid, dorsal cirri; ventral cirri smaller than dorsal cirri, ovoid, inserted near parapodial base.
Chaetae of several different types, up to 6 per fascicle in mid segments, arranged in the following way (dorso-ventrally): type 1 one, simple, bidentate upper (dorsal) chaeta, long, distally expanded with distinct serration; type 2 one large compound spiniger, with expanded serrated joint and long, smooth, extremely thin blade, which may be distally minutely bidentate (tip often twisted, or folded over and difficult to observe with certainty); type 3 two to three compound falciger with short, bidentate; 4 one, simple, bidentate lower (ventral) chaeta, long, slender distally tapering into blunt, smooth tip; both simple chaetae present from chaetiger 1. Pygidium, rounded lobes, with long lateral cirri.
Remarks. This species corresponds well with Exogone heterosetoides australis (see Hartmann-Schröder & Rosenfeldt, 1988 for details) described from Southern Ocean, Antarctic Peninsula (near Arctowski Polish Research Station, King George Island). The specimens differ in their development of antennae (completely missing in one voucher) and may therefore represent different regenerative stages, however in the best preserved specimen median antenna is about three times the length of the lateral ones as in description of holotype given by Hartmann-Schröder and Rosenfeldt (1988). Confusion with similar species Exogone heterosetosa (see separate entry and remarks under the species name Exogone cf. heterosetosa) likely happened in the past and it is possible that several species were lumped under the name Exogone heterosetosa, partially given by the lack of clarity on the length of median antenna in McIntosh's holotype. Also in E. heterosetosa reported in this study (see separate entry) the modified compound chaetae is more of a falcigerous form with short blade, not an obvious elongated form as described by Schröder & Rosenfeldt (1988) and as observed in FI specimens assigned here to E. heterosetoides australis. Careful re-examination of all material, particularly type material would be necessary to establish if it is in fact composed of several different species.