Smithsonian National Museum of Natural History

Original Description
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"Himantozoum obtusum sp.n. Fig. 37 A, C.

STATION DISTRIBUTION. Sub-Antarctic: South Atlantic Ocean, Sts. WS 85, WS 93, WS 225, WS 228, WS 229, WS 231, WS 246, WS 249, WS 783, WS 871.

GEOGRAPHICAL DISTRIBUTION. Patagonian Shelf (Discovery); off Patagonian Shelf down to 1098m.

(Discovery; 34.11.12.12 from Challenger St. 320).

HOLOTYPE. St. WS 228, off Patagonian Shelf.

DESCRIPTION. Colony usually bi- or triserial. Uniserial at base and occasionally quadriserial before a bifurcation. Bifurcation as in other species of Himantozoum. Rootlets as in H. antarcticum.

Zooecia like those of H. antarcticum except that they are smaller and are rounded distally, without angles or spines (Fig. 37 A). " Tubulure " (of Calvet) present. Avicularia absent.

Ovicells on median zooecia very shallow, without associated spines (Fig. 37 A, C). Embryo develops in large sac in body cavity.

REMARKS. This species, which is confined to the Patagonian region, is very similar to H. antarcticum. In addition to its more slender colony, and the differences already noted in the zooecia and ovicells, there appears to be a slight difference in the shape of the opercula, those of H. antarcticum being more angular, their shape correspond­ing to the shape of the distal end of the zooecium. In H. obtusum the opercula of the fertile zooecia are a little longer and rounder than the others. The Challenger specimen was found among unnamed material." (Hastings, 1943: 424-5)