Errinopora cestoporina Cairns 1983

Errinopora cestoporina Cairns, 1983a

(Fig. 4c; Fig. 9)

Errinopora cestoporina Cairns 1983a: 123–127, figs. 31e, 33a–g, 34a–b, map 6; Cairns 1983b: 428, table 1, 463, 465, 479; Cairns 2015: 116; Cairns & Macintryre 1992: 100, table 1, 106; Cairns & Lindner 2011: 12–17, table 1 and key, 22; Río Iglesias et al. 2012: 191; Bax & Cairns 2014: 108–110, table 1, map 5

Distribution. Patagonia, 42° S to 48° S; east of Burdwood Bank and south of Tierra del Fuego, 359– 384 m. New record off Mar del Plata, 819 m.

Material examined. USNM 60188 (holotype) off Burdwood Bank, Eltanin St. 1593 (54° 43–42’ S, 56° 37–39’ W); USNM 52655 (paratype) off south of Tierra del Fuego, Eltanin St. 1593 (54° 43–42’ S, 56° 37–39’ W); USNM 52655 (paratype) off south of Tierra del Fuego, Eltanin St. 740 (56° 06–07’ S, 66° 19–30’ W); USNM 60141 (paratype) off Burdwood Bank, Eltanin St. 1593; MACN-In-40658 off Mar del Plata, Argentina, St. 31 (38° 1.499’ S, 54° 44.171’ W), 819 m, August 2012.

Description. Fragment 1.7 cm long and about 2.5 mm wide, lacking base (Fig. 4c). Lateral branchlet 1.1 mm wide. Main branch slightly elliptical in cross section, with largest axis parallel to plane of growth.

Coenosteum white and porcellaneous. Microtexture reticulate-granular, with irregularly shaped granules that suggest a transition from an imbricate to a granular pattern. Coenosteal strips poorly delimited by round or very short slits, which penetrate the coenosteum deeply and are spaced from one another 29–85 µm (Fig. 9b).

Gastropores round, 0.3–0.4 mm in diameter and scattered uniformly on all surfaces of fragment. Gastropore tubes and gastrostyles were not examined due to scarcity of material, but tip of gastrostyles and a tube constriction are visible. Each gastropore bordered on abcauline margin by a straight or curved row of 5–8 dactylopore spines fused laterally with each other (Fig. 9a). When row is curve and surrounds gastropore forming a pseudocyclosystem, several dactylotomes face the gastropore. These rows protrude from branch surface like terraces arranged radially. Ocasionally a solitary adcauline spine may be present. Dactylopores of two types: those surrounded by a U-shaped spine (dactylotomes), 0.1–0.2 mm wide, whose fused spines form terraces, and those round and flush, around 0.1 mm wide and mostly aligned on the adcauline side of gastropores. Both types have a dactylostyle (Fig. 9c, e). Dactylostyles are simple or double rows of cylindrical bifurcate elements with blunt tips. Those illustrated in Fig. 9c and 9e are around 55 µm and 70 µm high, respectively.

Ampullae external and male. Those illustrated in Fig. 9d are around 0.5 mm in external diameter and have a prominent point with several efferent pores. Another two ampullae 1.3 mm wide with numerous pointed zones were observed as well.

Discussion. Specimen from the study area belongs to genus Errinopora due to the arrangement of primary dactylopores flanking gastropores in their proximal margin and forming pseudocylosystems, and to the presence of dactylostyles. It coincides with Cairns’ (1983a) original description of Errinopora cestoporina regarding pseudocyclosystem and ampullae characteristics. Errinopora cestoporina and E. fisheri are the only two species of the genus that lack dimorphic gastropores (Cairns & Lindner 2011), which agrees with the description of the studied material. No perforated mounds were observed such as those described for E. cestoporina by Cairns (1983a), probably due to the scarce material collected. Specimen differs from Cairns and Lindner´s (2011) description of secondary dactylopores (those without a spine) for the genus Errinopora, since they state a lack of dactylostyle. Flush dactylopores in the studied specimen do have a dactylostyle, which has the same shape as those present in the primary dactylopores. Here we propose adding in the description of the genus that secondary dactylopores do not always lack dactylostyles. We consider this specimen is indeed E. cestoporina despite this new character.

The only previous records of E. cestoporina are from Cairns (1983a) based on specimens from south of Tierra del Fuego and Burdwood Bank, and from Río Iglesias et al. (2012) based on specimens from Patagonia, from 42° S to 48° S within a depth range of 200–1500 m (specific depth not informed). The present work provides the third record of this species and extends the known distribution of E. cestoporina within SWA.