Orbinia

Blake, James A., 2017, Polychaeta Orbiniidae from Antarctica, the Southern Ocean, the Abyssal Pacific Ocean, and off South America, Zootaxa 4218 (1), pp. 1-145 : 89

Orbinia sp.

Phylo kupfferi: Hartman 1966: 107 –108 (in part). Not Ehlers, 1874.

Material examined. Antarctic Peninsula South Shetland Islands, Eltanin Sta. 6-437, 267– 311 m (1, LACM-AHF Poly 4994).

Description. A single specimen included among USNS Eltanin collections from Eltanin Station 437 and identified by Dr. Olga Hartman, as Phylo kupfferi is here referred to the genus Orbinia because posterior thoracic modified notosetae are not present. Other specimens in the same sample are referred to Phylo felix (see below).

Specimen mostly complete, 0.8 mm wide across anterior thoracic region, 7 mm long for 35 setigerous segments. Color light tan in alcohol with no pigmentation. Anterior end of body swollen through setiger 5. Thoracic region with 12 setigers; no posterior modified thoracic segments. Prostomium short, triangular, pointed on anterior margin; nuchal organs not observed. Peristomium short and narrow. Branchiae from setiger 6. Pygidium unknown.

Thoracic notopodia short with inconspicuous cirriform lobes on setigers 1–5; with the branchiae they become long and prominent on setiger 6, continuing posteriorly. Thoracic neuropodia with a single postsetal lobe through setiger 6, increasing to 3–4 from setiger 7, becoming continuous with subpodial ventral fringe on setiger 11; ventral fringe continuing posteriorly to abdominal setiger 16. Abdominal notopodia with elongate dorsal cirrus; abdominal neuropodia flattened, rounded apically, with distinct ventral cirrus. Interramal cirri not present.

Thoracic notosetae long, camerated capillaries arranged in two rows; thoracic neurosetae with three rows of heavy, curved uncini and a posterior row of heavy camerated capillaries. Individual uncini with smooth curved tip followed by transverse ribs further down shaft; with light microscopy, evidence of sheath on side opposite transverse ribs. Abdominal notosetae consisting of 3–4 long, narrow camerated capillaries and 2–3 delicate furcate setae; furcate setae with unequal tynes with thin webbing between. Abdominal neurosetae with 1–2 aciculae, sometimes emergent, with curved blunted tips and 2–4 long, thin, simple capillaries.

Remarks. This specimen was among a small collection from Eltanin Sta. 437 identified by Hartman (1966) as Phylo kupfferi , here referred to P. felix (see below); this single specimen is the only representative of the genus Orbinia reported to date from Antarctica and may represent an undescribed species, but due its incomplete nature and small size, it cannot be named at this time.

Distribution. Antarctic Peninsula, South Shetland Islands, 267–311.