Steginoporella perplexa Livingstone 1929

Steginoporella perplexa Livingstone, 1929

(Figs 1C, 4, 30)

Steginoporella neozelanica var. perplexa Livingstone, 1929: 67, text-fig. 2d, pl. 1, figs 8, 13. Steginoporella perplexa: Pouyet & David 1979a: 569, fig. 3B (part), 571, fig. 4C; Pouyet & David 1979b: 789; Gordon et al. 2009: 274 (fig. D), 290.

Material examined. NIWA 76404, Stn Z15617; NIWA 101450, Stn Z15929; NIWA 122670, Stn Z8662. Plus unregistered (non-separated) specimens in multispecies samples from NIWA Stations D896, Z8662, Z9671, Z9672, Z9673, Z9677, Z9678, Z9679, Z9680, Z9681, Z9686, Z9687, Z9688, Z9689, Z9896, Z9698, Z9700, Z9701, Z9702, Z9703, Z9707, Z9708, Z9710, Z9715, Z15617, Z15929, Z15935.

Diagnosis. Colony erect, large, planar, bilamellar and flabellate with undissected margin, up to 125 mm high and wide, attached to sediment grains and very small shells by basal tangle of rootlets. Colour in life pale brown. Zooids monomorphic, roundly subhexagonal but longer than wide (mean L/W = 1.81), widest at level of opercular pivots or median process. Cryptocyst occupying about half length of frontal surface, shelf depressed, flat, densely pseudoporous. Opercular opening delimited proximally by triangular opercular pivots and median process, with distolateral ‘wings’ that do not meet pivots or lateral margin; proximomedial foramen of moderate size, generally roundly quadrate, sometimes roundly triangular. Opercular sclerites reticulate, defining mostly 21–22 (sometimes fewer) areas of variable size. Thickness of sclerites may increase with age of zooid. Polypide, ancestrula and early astogeny not seen.

Measurements. In micrometres: ZL 1054±26, 1017–1100 (1, 10); ZW 582±19, 556–623 (1, 10); OpL 346±28, 300–383 (1, 10); OpW 474±37, 399–522 (1, 10).

Remarks. This is the largest species of Steginoporella in New Zealand and its fan-shaped colonies are highly distinctive. It is restricted to a small geographical area at the far north of North Island. Although locally common, its limited distribution to sandy bottoms where the scallop Pecten novaezelandiae Reeve is found makes it vulnerable to scallop dredging (Cryer et al. 2000).

Older parts of large colonies are an important substratum for a number of species of epizoic cheilostome and cyclostome bryozoans.

Distribution. Endemic to northern New Zealand: Three Kings Shelf in vicinity of Three Kings Islands, Cape Reinga and Spirits Bay; 30– 119 m.