Osthimosia minima, Hayward & Winston, 2011

Hayward, Peter J. & Winston, Judith E., 2011, Bryozoa collected by the United States Antarctic Research Program: new taxa and new records, Journal of Natural History 45 (37 - 38), pp. 2259-2338 : 2328-2329

Osthimosia minima sp. nov

( Figure 32 )

Material

Holotype. NMNH 11540043 : Eltanin cruise 5, station 219, 55 ◦ 47’ to 55 ◦ 52’ S, 66 ◦ 17’ to 66 ◦ 24’ W, 115 m, 23 September 1962; a pisiform colony 0.15 mm diameter, substratum not evident.

Description

Holotype colony a tiny, pisiform growth with a spiky appearance imparted by elongate, projecting peristomial avicularia, autozooids radiating outwards. Primary orifice as wide as long (0.125 mm), with a narrow, U-shaped sinus comprising onefifth total length; condyles broad, rounded. Proximal and lateral borders of orifice enclosed by two tall, thick, slightly curved peristomial folds, incorporating medioproximally a cylindrical avicularian cystid; rostrum subapical, oval, perpendicular to plane of orifice and facing distally, its distal rim finely denticulate, crossbar slen- der, without a columella, palate lacking. Avicularian cystid at least 0.52 mm long, but a slender, tapered portion extending distal to the rostrum was broken short in all instances. Vicarious avicularium with parallel-sided rostrum, 0.48 mm long, rounded and deeply cupped distally; crossbar very slender, no columella, palate with extensive foramen. Ovicell borne on distal rim of primary orifice; smoothly calcified, frontal surface with extensive area of uncalcified ectooecium, entooecium with indistinct marginal pores alternating with short ridges, similar to frontal tabula of Celleporina .

Etymology

Latin, minimus: least, the smallest species of Osthimosia present in the sample.

Remarks

The tiny, pisiform colony, columnar peristomial avicularia and narrow, U-shaped sinus of Osthimosia minima sp. nov. are all reminiscent of O. bicornis (Busk, 1881) , which is widely distributed in Antarctic and subantarctic realms. However, O. bicornis has paired peristomial avicularia, and the orificial sinus is bounded by thick, faceted condyles, quite distinct from the broad, flat condyles of the new species.

Figures

Figure 32. (A–C) Osthimosia minima sp. nov., Holotype. (A) Portion of colony showing peristomial avicularia, ovicells and a large vicarious avicularium; (B) detail to show the primary orifice. Scale bars: 0.25 mm (A), 0.05 mm (B).