ORIGINAL PAPER Emilia Rota á Gianmaria Carchini A new Polygordius (Annelida: Polychaeta) from Terra Nova Bay, Ross Sea, Antarctica Accepted: 27 August 1998 Abstract Polygordius antarcticus sp. nov. is described from benthic material collected at depths ranging be- tween 31 and 61 m in Terra Nova Bay, Ross Sea, during the 1987±1988 and 1988±1989 expeditions of the Italian National Research Program in Antarctica. This is the ®rst named species of the genus from Antarctic waters. Although no fully mature specimens were available, the new species appears unique in combining the following features: a regular pygidium, in¯ated and with a single ring of round adhesive pads, a conical prostomium with short antennae (only half as long as the prostomium) and shallow head fold, and a well-developed circulatory apparatus, with circumoesophageal commissures enter- ing the prostomium and long intersegmental commis- sures insinuating into the ventrolateral compartments of the trunk. These and other signi®cant features were in- vestigated by light and scanning electron microscopy. In the construction of the head and the scheme of the blood system, the new species resembles Polygordius triestinus Woltereck, described by Hempelmann in 1906, an aberrant species inhabiting muddy, anoxic sediments in the Adriatic Sea, but it diers signi®cantly from it in the shape of the mouth (in P. triestinus the upper lip is hy- pertrophied and strongly protruding) and the pygidium (in P. triestinus this region is stump-like and non-adhe- sive). The pygidium of P. antarcticus sp. nov. is encircled by 28±30 small adhesive pads, each with 15±20 glandular openings. Preterminal cirri are lacking, as are perianal appendages. The anus is surrounded by six to seven lobes of which the midventral is largest and longest. A world distribution map of the genus is provided. Introduction Members of the Polygordiidae are common inhabitants of marine coastal sands at various latitudes (Fig. 1). Their bodies are elongate and cylindrical, tapering at both ends. The prostomium has a pair of solid, non- grooved projections innervated from the anterior part of the brain (antennae; Fauchald 1977). The pygidium is generally expanded and encircled by adhesive glands; behind these glands, preterminal cirri or perianal papil- lae may be present (Table 1). The trunk surface is smooth, almost nematode-like, and shows little sign of external segmentation. All members of the family are classi®ed in the genus Polygordius Schneider, 1868, which lacks parapodia and chaetae. The chaetate Chaetogordius canaliculatus Moore, 1904 described ``from a couple of fragmented specimens in association with marine Oligochaeta on Cape Cod'', yet never re- discovered (Hermans 1969), is regarded today as an in- valid taxon (Westheide 1990). Like the protodrilids and saccocirrids, but unlike all other interstitial polychaetes, Polygordius worms devel- op with pelagic planktotrophic larvae (Hermans 1969; Westheide 1990). These are of two types: in the ``exo- larva'' the larval body becomes gradually elongated by addition of new segments; in the ``endolarva'' the de- veloping segments remain folded up inside the hypo- sphere until a more or less abrupt metamorphosis (Woltereck 1902; Remane 1932; Dawydo 1959). Until recently (Lenihan and Oliver 1995; Rota and Carchini 1996), the collection of giant endolarvae in the South Atlantic during the German Deep Sea Expedition aboard the Valdivia (1898±1899) (Woltereck 1905) rep- resented the southernmost record of these animals. During the third (1987±1988) and fourth (1988±1989) expeditions of the PNRA (Italian National Research Program in Antarctica) to the Ross Sea, one of the au- thors (GC) collected abundant benthic material of Polygordius at various depths in the coastal stretch ad- jacent to the Italian Base in Terra Nova Bay (Rota and Polar Biol (1999) 21: 201±213 Ó Springer-Verlag 1999 E. Rota (&) Dipartimento di Biologia Evolutiva, UniversitaÁ di Siena, Via Mattioli 4, I-53100 Siena, Italy e-mail: rota@unisi.it, Fax: +39-577-283450 G. Carchini Dipartimento di Biologia, UniversitaÁ di Roma ``Tor Vergata'', Via della Ricerca Scienti®ca, I-00133 Rome, Italy