Bifaxaria submucronata Busk, 1884

Matsuyama, Kei, Janssen, Annika, Arbizu, Pedro Martínez, Martha, Silviu O. & Freiwald, André, 2014, Bryozoans from RV Sonne deep-sea cruises SO 167 ‘ Louisville’ and SO 205 ‘ Mangan’, Zootaxa 3856 (1), pp. 100-116 : 107-108

Bifaxaria submucronata Busk, 1884

( Fig. 5 , A–B, F–H)

Bifaxaria submucronata Busk, 1884: 80 , pl. 13, figs 1, 1a; Gordon 1993: 309, figs 3a–d, 18a–e (cum syn.).

Material examined. SMF 15003, SO 205 Stn 61, 13.174° N – 3.194° N, 118.106° W – 118.0953° W, Equatorial East Pacific, 3996–4007 m, collected 16 May 2010. Bleached.

Description. Colony candelabriform, jointed, with two lateral, slightly curved branches emanating from a branching point; mode of attachment to substratum not seen. Branches formed by laterally compressed zooids arranged in two alternating rows ( Fig. 5 , A–B). Lateral suture prominent, carinate, forming a sinuate line curving from avicularium to avicularium ( Fig. 5 , B). Outer shield layer umbonuloid, with mostly 3 rows of pores along main axis and additional smaller pores along sutures; frontal suture with distinct carina, forming a tip in middle of proximal orificial rim ( Fig. 5 , F). Inner orifice subcircular, proximal boundary rather straight; outer secondary orifice transversely D-shaped, with straight proximal rim. Avicularia distolateral, one on each side of orifice in distal third ( Fig. 5 , F), small and circular with tiny mandibular pivots that do not touch ( Fig. 5 , G). Spinocystal costae sinuous, touching each other thus leaving intercostal spaces ( Fig. 5 , H). Fertile zooids not observed.

Measurements.

Zooid length 785–1023 µm, σ = 82 µm, N = 6; width 327–403 µm, σ = 24 µm, N = 6

Branch width 451–552 µm, σ = 41 µm, N = 6

Orifice diameter 193–227 µm, σ = 12 µm, N = 6.

Remarks. Distinguishing B. submucronata from other similar species, mainly B. compacta Gordon, 1993 , B. gracilis Gordon, 1993 and B. modesta Gordon, 1993 , can be achieved by comparing zooidal dimensions and the shape and dimensions of the spinocystal costae. In B. modesta the costae are simple and do not touch each other, whereas in all other species they are somewhat sinuous and adjacent costae touch each other. Bifaxaria submucronata can be distinguished from the other two species by both its greater zooidal length and width compared with B. gracilis and greater zooidal length compared to B. compacta .

Figures

FIGURE 5. A – B, F – H, Bifaxaria submucronata Busk, 1884. A, frontal view of stem fragment. B, lateral view. F, orificial area, frontal view. G, close-up of oral avicularium. H, underside of concealed costal shield. C – E, Domosclerus sp. C, lateral view of stem fragment. D, single zooid and neighbours. E, orificial area. Scale bars: A – C, 1 mm; D, 300 Μm; E – F, H, 100 Μm; G, 30 Μm.