(Figs. 10, 11)
Errinopsis fenestrata Cairns 1983a: 80–82, figs. 1i, 10a–g, map 3; Cairns & Macintryre 1992: 98, table 1; Cairns 2011: 9, fig. 7a; Cairns & Zibrowius 2013: 18–19, figs. 9a–i, 49, table 2, 51; Bax & Cairns 2014: 108–111, table 1, map 6
Distribution. Drake Passage and Shag Rocks, 280–340 m; South Africa: Eastern Cape Province, 174– 250 m. New record off Mar del Plata, 1398 m.
Material examined. USNM 52693 (holotype) off Drake Passage, Eltanin St. 254 (59° 49.4’ S, 68° 51.7’ W); MACN-In 40646 off Mar del Plata, Argentina, St. 59 (37° 49.688’ S, 54° 5.236’ W), 1398 m, September 2013.
Description. Colony uniplanar and 6.0 cm wide, attached to dead specimen of scleractinian Bathelia candida through several non-expansive bases (Fig. 10). Branching dichotomous and highly anastomotic producing a fenestrate fan. Branches rectangular to elliptical in cross section (Fig. 11a), with larger axis perpendicular to plane of growth. Basal branches 1.0– 1.4 mm wide at shorter margin of cross section and around 2.0 mm wide at longer margin. Diameter of branches more or less constant from base towards tips and between branches, except new branchlets, which may be less than 1.0 mm wide.
Coenosteum compact, white and porcellaneous. Microtexture more or less linear-granular. Strips 24–59 µm wide and parallel to each other, sometimes more diagonal than parallel to branch axis, ocasionally bifurcating and rejoining. Slits deep, short or long. Granules rounded, flat and sparse in some zones and more conical and clustered in others, resulting in flat or more concave strips, respectively. Fig. 11b illustrates transition from granular-imbricate texture to smoother granular one.
Gastropores round, 0.2–0.3 mm wide (n=7) and arranged in anterior and antero-lateral surface of branches (Fig. 11a). Branchlet usually forms at margin of gastropore (Fig. 11a). In more or less horizontal branches, branchlets generally originate at right margin of gastropore and develop diagonally downwards towards left on inferior face of branch and diagonally upwards towards left on superior face of branch. In more or less vertical branches, branchlets originate at superior margin of gastropore and develop downwards. Gastropore tube peripheral and short, around 0.54 mm long, with spherical basal section which occupies about 2/3 of tube and encompasses most of gastrostyle (Fig. 11e). Towards surface of coenosteum a significant constriction transforms shape of superior section of tube to cylindrical, which surrounds gastrostyle tip. Gastrostyle robust (H:W=2), around 0.41 mm high and spindle-shaped, with wide smooth base; central section 0.22 mm wide at maximum diameter, bearing diagonal rows of blunt spines fused with each other, and tip that reaches beginning of cylindrical section of gastropore tube.
Dactylopores of two types: those round, 32–48 µm wide (n=6), scattered uniformly on coenosteum and partially raised from surface (Fig. 11a, b) and those slit-like, 50–70 µm wide, placed along side of slender spines (Fig. 11c). Following direction of a branchlet developing downwards into a fenestrum, dactylotomes (slits) are oriented towards distal end of branchlet, thus spines bearing them are abcauline with respect to that branchlet. Spines lacking slit often present as well and higher and more slender than slitted ones (Fig. 11d). Dactylopore spines and branchlets more frequent at lateral and antero-lateral faces of branches. Branchlets seem to originate from dactylopore spines that extend and divide producing, first, additional dactylopores and, secondly, a new gastropore. Ampullae absent.
Discussion. Errinopsis fenestrata was originally described by Cairns (1983a) based on specimens from Drake Passage at 280–340 m depth. Cairns and Zibrowius (2013) described specimens from South Africa at 250 m depth. The specimen from off Mar del Plata differs from the one described by Cairns (1983a) only in the width of coenosteal strips and of dactylopores. It is necessary to study more material in order to conclude whether this is normal variability within the species. The same differences exist between the Mar del Plata specimen and the material described by Cairns and Zibrowius (2013). Regarding coenosteum colour, it is orange in specimens from South Africa and white in those from off Mar del Plata and in type material. This may be due to natural variability within species. Cairns and Zibrowius (2013) mention Shag Rocks within the distribution range of E. fenestrata, but this location is not represented by specimens described in that paper nor in papers they cite. Bax and Cairns (2014) mention new records of this species in Burdwood Bank, South Georgia and Shag Rocks, but hitherto descriptions of this material haven´t been published. This publication provides an extension of the known geographical and bathimetric distribution of E. fenestrata.