Melicerita lingulata Liu and Hu, 1991

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 : 2281-2283

Melicerita lingulata Liu and Hu, 1991

( Figure 11 )

Melicerita lingulata Liu and Hu, 1991: 49 , 147, figs 9A–H.

Material

Eltanin Cruise 7, station 457, locality uncertain, 6 February 1963; 16 colonies. Eltanin cruise 6, station 410, 61 ◦ 18’ to 61 ◦ 20’ S, 56 ◦ 09’ to 56 ◦ 10’ W;> 100 fragments, up to 25 mm long.

Description

Juvenile colony triangular in outline, sharply tapered proximally, broadest at the straight distal edge; broadly club-shaped, with autozooids on both faces and along the edges; apparently budded from a single ancestrular zooid, anchored in (presumed) soft sediments by three thick, cylindrical, annulate rhizoids, each arising from a frontally modified autozooid, within three astogenetic generations of the ancestrula; distal ends of rhizoids finely divided into coiling tendrils. Older colonies to 25 mm long, c. 4 mm wide, flat, straight and parallel-sided. Autozooids disposed in alternating whorls, from two immediately above the ancestrula to a distal whorl of 10 in the largest colony. Autozooid shape varies in relation to astogeny, in the first few generations oval to hexagonal, longer than wide; broadly hexagonal and wider than long in later generations; each bounded by a thin cryptocystal rim and separated by a distinct suture. Cryptocyst flat, calcification coarsely and evenly nodular. Opesia in distal half of autozooid, wider than long, with a thickened, raised rim, proximal edge straight in early ontogeny, later distinctly convex, with a narrow shelf within, produced close to each proximo-lateral corner into a short, blunt denticle; two opposing denticles present on the distal rim, in some zooids with a thickened ridge linking them; all denticles most pronounced in later astogeny. Endotoichal ovicells evident as low swellings on the cryptocysts of the two succeeding autozooids, with low crescentic aperture immediately distal to, and only slightly smaller than the opesia of the brooding zooid. In each of the triangular juvenile colonies the broad distal edge is capped by flat, polygonal kenozooids, each with a minute central foramen. In the two smallest specimens the distal edge of the colony was bounded by membranous body wall, with a new generation of partially budded autozooids visible beneath it. No avicularia noted. Proximalmost autozooids bear convex plates of cryptocystal calcification projecting above the frontal shield, from the proximal edges of which the rhizoids originate. In some marginal autozooids of the larger colonies the opesia is partially occluded by smooth calcification.

Measurements

All measurements are mean ± SD: Juveniles – colony length n = 15, 4.20 ± 0.61 mm; colony width n = 15, 3.35 ± 0.41 mm; autozooid length n = 10, 0.57 ± 0.04 mm; autozooid width n = 10, 0.58 ± 0.06 mm; opesia length n = 10, 0.16 ± 0.01 mm; opesia width n = 10, 0.23 ± 0.01 mm; Older colonies – autozooid length n = 10, 0.55 ± 0.03 mm; autozooid width n = 10, 0.58 ± 0.03 mm; opesia length n = 10, 0.16 ± 0.01 mm; opesia width n = 10, 0.20 ± 0.01 mm.

Remarks

The 16 specimens from Eltanin cruise 7, station 457 were of a similar size ( Figure 11C ) and there were no significantly larger colonies, or fragments of larger colonies. The flat distal edge of each colony ( Figure 11D ), and distal margins, were capped with kenozooids, suggesting that growth had ceased (except for one exception noted in the description), and implying a short generation time. Hence, colony shape, size and life history might be additional specific characters. However, the material from the second locality, consisted of more than 100 colonies with a blade-like morphology; all had a constant width of around 4 mm. Some were evidently fragments, and most were damaged proximally; only one specimen was bifurcate but it was not apparent whether this was normal colony architecture or whether it represented redirected growth following damage. A number of these larger specimens retained their proximal portions, which were identical to the triangular juvenile colonies. Many of these colonies showed one or more growth checks. Autozooid morphology in these large specimens was closely similar to that of the small colonies; autozooids were proportionately broader towards the colony margins, but dimensions of the opesiae were the same, although the denticles were more pronounced. The largest complete specimen, ancestrulate and with undamaged growing edge was 19 mm long, and the largest specimen overall, damaged both distally and proximally, was 25 mm long. Ovicells were present in 14 of the juvenile colonies, borne by autozooids of the last two astogenetic generations, and within 10 astogenetic generations from the ancestrula in the larger colonies.

Fourteen species of Melicerita have been described from cold temperate to polar waters of the southern hemisphere ( Moyano 1997), three of which appear to be endemic to Antarctica ( Hayward 1995). Melicerita lingulata may be distinguished from all of these by its flat autozooids, with distally rounded outline, its straight-edged opesia and its simple, comparatively large ovicell aperture. The tiny juvenile colonies appear even more distinctive, the flat angular outlines of autozooids characteristic of most Melicerita species not being apparent until much later astogenetic stages. In this context, the colony of Euginoma conica Gordon, 1986 , from New Zealand bears a striking resemblance to the first three astogenetic generations of Melicerita lingulata . Liu and Hu (1991) described this species from a single sample collected north of the Antarctic Peninsula (62 ◦ 51.6’ S, 58 ◦ 07.5’ W, 654 m). They did not state how many specimens the sample comprised, and although their description was comprehensive and their figures showed the distal edge of a large colony, and the ancestrulate basal portion of a colony, it was not clear whether it included the triangular juvenile colonies described here.

Figures

Figure 11. Melicerita lingulata, (A, B) Eltanin (6) stn. 410. (A) Group of mature zooids, one with a damaged ovicell; (B) part of colony to show branch margin. (C, D) Eltanin (7), stn. 457. (C) a complete juvenile colony; (D) detail of juvenile colony to show kenozooids and an ovicelled zooid at its distal edge. Scale bars: 0.1 mm (A, B, D), 1.0 mm (C).