Errinopsis reticulum Broch, 1951a

Bernal, M. C., Cairns, S. D., Penchaszadeh, P. E. & Lauretta, D., 2021, Stylasterids (Hydrozoa: Stylasteridae) from Mar del Plata submarine canyon and adjacent area (southwestern Atlantic), with a key to the species off Argentina, Zootaxa 4969 (3), pp. 401-452 : 22

Errinopsis reticulum Broch, 1951a

( Fig. 12b ; Fig. 13 )

Errinopsis reticulum Broch 1951a: 37–41 , pl. 2, fig. 2, pl. 3, figs. 1, 2, text figs. 3–7; Boschma 1957: 59; Boschma 1966: 117; Lowe 1967: 93–95, pl. 8, fig. a, text figs 14a–c; Boschma & Lowe 1969: 15, pl. 5, map 4; Cairns 1983a: 78–80, figs. 1g –h, 9a–h, map 3; Cairns 1983b: 428, 457–458, figs. 10a–h, 502, fig. 27c; Cairns & Macintryre 1992: 98, table 1; Río Iglesias et al. 2012: 191; Bax & Cairns 2014: 108–110, table 1, map 6

Distribution. Patagonia, 42° S to 48° S; area between Tierra del Fuego, Burdwood Bank and Malvinas Islands, 250– 771 m. New record off Mar del Plata, 854 m.

Material examined. USNM 1099407 off Burdwood Bank, Lawrence M. Gould St. 8 (54° 22.9’ S, 61° 53.0’ W); MACN-In 40645 off Mar del Plata, Argentina, St. 11 (37° 59.258’ S, 54° 41.436’ W), 854 m, August 2012 .

Description. Uniplanar growth. Branch anastomosis frequent and regular, producing fenestrate fans. Two main fans fuse at base, resulting in a basket-shaped colony. Secondary, more fragile fans grow between them, more or less transverse to them. ( Fig. 12b ). Branches rectangular to elliptical in cross section, with larger axis transverse to plane of fan and width relation of up to 1:4 between axis. Thickest branch, measured at base where main fans fuse, is 7.3 x 5.0 mm wide. New branchlets may measure down to 1.0 mm. Fenestrae variable in size and shape ( Fig. 13a ).

Cenosteum compact, grey and eroded, smooth on posterior side of main fans. Coenosteal strips 36–74 µm wide and poorly granular, placed longitudinally along branches where linear slits are present ( Fig. 13c ). In more eroded parts of colony slits are reduced to pores and strips are poorly defined.

Gastropores round, 0.26–0.46 mm wide (average 0.38 mm, n=18, σ=0.05), more or less aligned at anterior and antero-lateral face of branches, mainly at the latter ( Fig. 13d ). Gastropore tube short and peripheral ( Fig. 13b ). Basal two-thirds of tube consist of cylindrical chamber rounded at the top, which encompasses almost entire gastrostyle. At level of gastrostyle tip, tube constricts considerably into an upper cylindrical chamber. Gastrostyle in Fig. 13b spindle-shaped, 0.37 mm tall and 0.14 mm in maximum width (H:W=2.6). Although eroded, vertical ridges of spines are distinguishable. Gastrostyle in Fig. 13e more elongate, (H:W=2) and bears blunt spines fused with each other in horizontal layers.

Dactylopores of two types: those round, 40–60 µm wide and raised on mounds and those surrounded by a Ushaped spine. They are distributed in all surfaces of branches, although less frequent at posterior side. Only one Ushaped spine, with a dactylotome around 67 µm wide, was identified under a dissecting microscope in a less eroded zone of colony. Anterior and antero-lateral sides of branches bear rounded porous stumps which may be eroded bases of dactylopore spines, approximately as wide as gastropores.

Ampullae spherical, total or partially sunken in coenosteum, and up to 1.1 mm in external diameter. Sex unknown. The silhouette of a scapellid barnacle attached to one of branches was identified, completely covered in coenosteum.

Discussion. Errinopsis reticulum was originally described by Broch (1951a) based on specimens collected off South of Malvinas Islands at 200 and 267 m depth. The next records were from Cairns (1983a) in Malvinas, Burdwood Bank and Tierra del Fuego. Cairns (1983b) differs with Broch (1951a) in the description of dactylopore spines, stating that there are two types: the low, round ones with an apical pore (dactylopores on mounds) and the long, conical spines with a slit on one side, in contrast with Broch (1951a), who states there is no dimorphism, that long spines derive from low ones with an apical pore, and that there are intermediate forms of spine as evidence of this hypothesis. The specimen from off Mar del Plata has both types of dactylopore and coincides with Errinopsis reticulum in growth and branching form, pore arrangement, gastrostyle and gastropore tube characteristics and in its robustness. Slitted dactylopore spines were not analyzed since most of them were worn. The specimen differs with material described by Cairns (1983a) in coenosteum color, which he described as bright orange to pink but is mainly grey or pale orange in the Mar del Plata specimen. Gastropores and dactylopores are wider than those reported by Cairns (1983a). The faded color, larger pore diameter and lack of almost all U-shaped dactylopore spines in specimen from Mar del Plata are probably due to erosion. It was probably already dead when collected, since it was mostly covered by a layer of sponge and material in decay. Río Iglesias et al. (2012) reported a new record of this species since Cairns and Macintryre (1992) based on specimens from Patagonia from 42° S to 48° S within a depth range of 200–1500 m (specific depth not stated). Bax and Cairns (2014) mentioned the occurence of E. reticulum in South Georgia and Cape Horn, but hitherto the descriptions and specific locations of these specimens have not been published. This new record off Mar del Plata extends the known distribution of E. reticulum within SWA.

Figures

FIGURE 12. (a) Terminal fragments of Sporadopora dichotoma. (b) Colony of Errinopsis reticulum.

FIGURE 13. Errinopsis reticulum. (a) Anastomosis and variably-sized fenestrae. (b) Eroded gastrostyle. (c) Coenosteal texture and raised dactylopores. (d) Gastropores aligned on antero-lateral face of branches. (e) More elongate gastrostyle.