Membranicellaria dubia (Busk)

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 : 2284-2286

Membranicellaria dubia (Busk)

( Figures 10C, D ; 12 )

? Melicerita dubia Busk, 1884: 97 , pl 33, fig. 10.

Membranicellaria dubia: Levinsen, 1909:207 , plate 7, figs 2a–e.

Material

Lectotype (chosen here). BMNH 1887.12 .9.438, Challenger station 320, 37 ◦ 17’ S, 53 ◦ 52’ W, 600 fm (1097 m).

Other material. BMNH 1944.1 .8.231, same data as for lectotype (probably part of same colony). Eltanin cruise 27, station 1870, 71 ◦ 17’ to 71 ◦ 16’ S, 171 ◦ 33’ to 171 ◦ 29’ E, 741– 659 m, 14 January 1967 .

Description

Colony erect, bilaminar, branching irregularly, developing broad, flat lobes. Autozooids with angular outline, quadrangular to hexagonal, separated by distinct raised sutures; operculum with a brown, thickened peripheral sclerite; frontal membrane underlain by a thickly calcified, shallowly concave cryptocyst, with coarsely nodular surface; opesia oval, symmetrical, situated in centre of cryptocyst and equivalent to half total zooid length; vertical walls of zooids deep, with large multiporous septula in a single row basally. Ovicell immersed, apparent as an arched, trifoliate, apertural rim on the distal side of the maternal zooid and low swellings in the proximal cryptocyst of the two distally succeeding autozooids; with an independent orifice, marked by a brown peripheral sclerite, distal to that of the maternal zooid, but its cavity not completely separated from that of the zooid. In autozooids towards the tapered proximal end of the colony the opesia is obscured by a frontally curving plate of cryptocystal calcification, which eventually completely occludes it, except for a pair of small lacunae distally; proximally, the edge of this plate is arched and curved, delimiting a ring which perhaps indicates the origin of a cuticular rhizoid. Edges of colony branch thin, edged with sporadic vicarious avicularia and small kenozooids, with reduced opesiae. Avicularia elongate, distributed along branch edges, with a raised, hood-like, semi-elliptical rostrum, directed distally; palate with an elongate oval opesia, mandible articulating against a pair of knob-like condyles.

Measurements

All measurements are for n = 20, mean ± SD: autozooid length 0.99 ± 0.11 mm; autozooid width 0.81 ± 0.12 mm; opesia length 0.48 ± 0.08 mm; opesia width 0.37 ± 0.04 mm.

Remarks

The lectotype specimen is a fragment of a colony, 27 mm long, 17 mm greatest width, just before a distal bifurcation; the second specimen from Challenger station 320 is a smaller fragment, 8 mm long, 10 mm wide, and is probably part of the lectotype colony. The USARP specimen represents only the second record of this species, and demonstrates its mode of attachment to the substratum. It is also fragmentary, 18 mm long, 8 mm wide, and tapered proximally, where a preponderance of zooids show occluded opesia inferred to represent the bases of anchoring rhizoids .

Busk’s type series was collected from a deep-sea station off the edge of the Patagonian Shelf, at 37 ◦ S, whereas the USARP specimen was collected off Cape Adare, at 71 ◦ S in the eastern Ross Sea. There are very few faunistic data for Antarctic and subantarctic deep-sea environments and it is not possible to conclude an unusual disjunct distribution for M. dubia .

Superfamily BIFAXARIOIDEA Busk, 1884

Figures

Figure 10. (A,B) Stomhypselosaria simplex sp. nov., Paratype. (A) Part of branch, with dichotomy; (B) detail of opesia. (C, D) Membranicellaria dubia, Eltanin (27) stn. 1870. (C) Autozooids in late ontogeny, with occluded opesiae; (D) auotozooids in early ontogeny (top), and others with developing occlusions. Scale bars: 1.0 mm (A), 0.1 mm (B, C, D).

Figure 12. Membranicellaria dubia, NHL 1887.12.9. 438. Ovicelled zooids. Scale bar: 0.5 mm.