Osthimosia sirena, Gordon, 2009

Gordon, Dennis P., 2009, New bryozoan taxa from a new marine conservation area in New Zealand, with a checklist of Bryozoa from Greater Cook Strait, Zootaxa 1987, pp. 39-60 : 48

Osthimosia sirena n. sp.

(Figs 19–21)

Material examined. Holotype: NIWA 46362 . Paratypes: NIWA 46363 , 46364 . All types from Pterocladia lucida , c. 5 m depth, Siren Rocks, Taputeranga Marine Reserve , collected by Sheryl Miller 7 October 2007 .

Etymology. Alluding to the occurrence of the species on algae growing on the Siren Rocks in the prospective marine reserve.

Description. Colony encrusting, small, c. 5 mm diameter, forming small pale orange mound. Zooids with indistinct boundaries, 0.39–0.45 mm long and 0.22–0.26 mm wide when recumbent, with anterior end semierect. Peristome forming rounded knob-like umbo set in avicularium on anterior face; an additional lateraloral avicularium in many orifices. Primary orifice concealed in mature zooids, 0.12–0.15 mm long, 0.11–0.12 mm wide, with narrow, parallel-sided sinus, condylar shoulders rather broad. No spines. Adventitious avicularia numerous, variable in length, up to 0.22 mm long and 0.15 mm wide, subspathulate, rostral palate well developed, foramen roundly triangular. Interzooidal furrows between autozooids and avicularia occupied by areolar pores of variable diameter. Ovicell subglobular, partly immersed, more or less smooth and lacking tabula or foramen.

Remarks. Ten other described species of Osthimosia are known in New Zealand waters ( Uttley & Bullivant 1972; Gordon 1984, 1989; Taylor et al. 1989). Osthimosia sirena differs from all of them in the sum of its characters; diagnostic features include the narrow orificial sinus, and the details of the adventitious avicularia, especially the relative shape and proportion of the rostral palate and palatal foramen. The species is epiphytic on Pterocladia lucida , occupying the same habitat as Celleporina wellingtonensis with which it cooccurs.