Microporella hyadesi

Microporella hyadesi (Jullien, 1888)

Fig. 6; Table 4

Fenestrulina hyadesi Jullien, 1888: 44, pl. 4, fig. 7 (giVen as Fenestrula in text but Fenestrulina on plate and caption).

Microporella hyadesi – López-Gappa 1975: 435, pl. 1, fig. 1, pl. 2, fig. 3. — López-Gappa & Lichtschein 1990: 26, pl. 8, fig. 3. — Hayward & Ryland 1990: 1282, fig. 10a. — Moyano 2000: table 1.

non Microporella hyadesi – Brown 1952: 254, figs 186–187.

FALKLAND ISLANDS • 1 specimen; depth 74–75 m; 24 Mar. 1927; Discovery Expedition, St. WS 84; Recent; NHMUK 1990.10.22.14 (Fig. 6 A–D) • 1 specimen; depth 166 m; 20 Jul. 1928; Discovery Expedition, St. WS 249; Recent; NHMUK 1990.10.10.25 (Fig. 6 E–F) • 1 specimen; west end of Magellan Strait; depth 66 m; 16 Mar. 1934; Discovery Expedition, St. 1321; Recent; NHMUK 1990.10.31.12 (Fig. 6 G).

COLONY. Erect, bifoliate, broad branches fused at edges to form a boxwork colony; growing edge intermediate between a smooth and a stepped edge; interzooidal communication not observed.

AUTOZOOIDS. Rounded rectangular to hexagonal, longer than wide (mean L/W = 1.67), distinct with interzooidal boundaries marked by thin band of slightly raised calcification on either side of a narrow grooVe. Frontal shield flat to Very slightly conVex, pustulose; marginal areolar pores numbering about 10, elongate near growing edge, becoming smaller, equidimensional and almost indistinguishable from pseudopores, except for those at the proximolateral corners of the zooid which remain larger (diameter 20–40 µm); pseudopores numerous (about 50), small (diameter 5–15 µm), irregularly scattered among pustules.

ORIfICE. TransVersely D-shaped, significantly wider than long, hingeline with about 20 equal-sized teeth; oral spines lacking.

ASCOPORE fIELD. A narrow band of gymnocystal calcification, positioned at approximately same leVel as orifice but slightly depressed relatiVe to the adjacent frontal shield, located ca 50–60 µm from the orifice hingeline, separated from it by non-porous pustulose cryptocyst; circular to transVersely elliptical (diameter 50–60 × 60–70 µm), opening C-shaped, 5–10 × 35–40 µm, with tiny radial denticles, and a circular tongue projecting from distal edge.

AVICULARIUM. Single, moderately large, present in the majority of autozooids, sometimes lacking in smaller zooids, especially immediately following row bifurcations; positioned level with the ascopore, oriented distolaterally, usually at about 60° to the long axis of the autozooid; crossbar calcified; opesia semielliptical; rostrum short, broadly subtriangular with concave sides, the distal end rounded, distinct channel present. Mandible in dried material narrow, short (ca 50–65 µm) and pointed triangular.

OVICELLS. Very large, sometimes covering frontal shield of distal zooid as far as ascopore, bulbous, usually a little longer than wide, personate or semi-personate with variably-developed lobes extending proximally of orifice, calcification fabric similar to frontal shield but with finer pustulation, smoothly continuous with frontal shield of distal zooid; small pores scattered over entire surface, denser close to lateral and distal margins; secondary orifice of personate oVicellate zooids of reduced length, typically boat-shaped, the distal edge concave, the proximal edge convex.

This species has been recorded from the subantarctic, Cape Horn and Tierra del Fuego. Records from the Indian Ocean (Thornely 1912) and New Zealand (Brown 1952; Powell 1967) are probably misidentifications, the latter possibly M. ordo (see Di Martino et al. 2017: fig. 6). It is Very common in material from several widely dispersed Discovery Stations from depths of 49 to 341 m in the South Atlantic around Cape Horn, the Falkland Islands, Burdwood Bank, the southern Patagonian Shelf, Shag Rocks and South Georgia (Hayward & Ryland 1990). Many of the colonies show extensive circular boreholes, about 0.12 mm in diameter, which penetrate autozooidal frontal shields and ovicells (Fig. 6 C– D). Similar boreholes were interpreted by Wilson & Taylor (2006) as evidence of boring predation. Often the boring is repaired by a plug of calcification secreted from the underside, or by an adVentitious aVicularium (Fig. 6C). Bored zooids may possess an additional orificial rim with a new hingeline within the original orifice, representing intramural budding, or haVe a sealed orifice (Fig. 6D). Teratology was observed in both autozooids (Fig. 6E) and ovicells (Fig. 6F).