Fenestrulina specca Gordon, 1989

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 : 2311-2313

Fenestrulina specca Gordon, 1989

( Figure 25A, B )

Fenestrulina specca Gordon, 1989: 61 , pl. 32, figs D,E.

Material

Eltanin cruise 6, station 370: 53 ◦ 54’ to 53 ◦ 55’ S, 64 ◦ 36’ to 64 ◦ 52’ W, 104–115 m, 12 December 1962; several fragmentary colonies.

Description

Colony encrusting, unilaminar. Autozooids hexagonal, but irregularly so at division of rows, gently convex, separated by deep grooves, revealing vertical walls. Primary orifice wider than long, occupying approximately one-fifth total frontal length of zooid; D-shaped, the straight proximal border with a minute denticle in each corner, revealed by SEM; three or four short, slender and indistinct spines evenly spaced around distal rim of orifice. Frontal shield smoothly calcified, vitreous; ascopore situated at mid-length of the zooid, deeply crescentic, with denticulate edge; distance between proximal edge of orifice and distal edge of ascopore rim equivalent to length of orifice. Numerous pores in frontal shield: a single series along the border between the frontal shield and the lateral walls; a double series between the orifice and the ascopore, and others scattered laterally so that only the mid-proximal region of the frontal shield lacks pores; pores small and round, each partly occluded by a delicate sieve plate, resembling a holothurian ossicle. Ovicell prominent, slightly wider than long, with a single series of small pores closely spaced around its periphery; calcified entooecium finely granular, imperforate, with indistinct, radiating frontal ridges.

Measurements

For all measurements, n = 20, mean ± SD: autozooid length 0.62 ± 0.05 mm; autozooid width 0.41 ± 0.05 mm; orifice length 0.13 ± 0.01 mm; orifice width 0.17 ± 0.01 mm.

Remarks

Fenestrulina specca was described by Gordon (1989) from six stations in Milford Sound, and another to the southwest of Stewart Island, southwest South Island, New Zealand. This new record is therefore from a locality so remote from the type locality that it might be considered unlikely, recent systematic and morphological research usually demonstrating that such broad geographical ranges are founded on misidentifications. In this case, comparison of the southwest Atlantic material with Gordon’s figures of the New Zealand specimens reveal extraordinary similarity. The size range of the autozooids (length 0.52–0.69, width 0.36–0.5 mm) is almost exactly within that cited by Gordon (1989: 61) for the New Zealand material (0.38–0.64 by 0.21 – 0.51 mm), and orifice size and morphology, size, distribution and morphology of the frontal shield pores, and ovicell morphology, are all practically identical in the two sets of figures. The only apparent difference relates to the ascopore, which in the southwest Atlantic specimens ( Figure 25A, B ) is recessed within a low rim; in the figured New Zealand material ( Gordon 1989: plate 32, figs D, E) the ascopore forms a rather shallow C-shape, whereas in the new specimens it appears more deeply rounded. However, Gordon’s figures show only four ascopores, more are shown for the southwest Atlantic material, and indicate a range of morphology from shallow to deeply rounded. Further material, including ancestrulae and early astogenetic stages, and encompassing a more complete ontogenic series, may indicate that these two entities, distributed on opposite sides of the Antarctic continent, represent distinct species; genetic congruence is unlikely but at present they cannot be distinguished on morphological grounds.

Figures

Figure 25. (A, B) Fenestrulina specca. (A) Group of autozooids; (B) ovicelled zooids. (C,D) Fenestrulina asperula. (C) Ovicelled zooids; (D) a single autozooid at the colony margin. Scale bars: 0.25 mm (A, B, C), 0.1 mm (D).