Stellapora echinata ( Moseley, 1879 )

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 : 32-35

Stellapora echinata ( Moseley, 1879)

( Figs. 18 , 19 )

Spinipora echinata Moseley 1879: 447–449 , pl. 34, fig. 3, pl. 35, fig. 4, pl. 38; Moseley 1881: 55–57, pl. 1, fig. 3, pl. 2, fig. 4, pl. 5; Boschma 1964: 293

Errina (Spinipora) echinata: Hickson 1912: 881 , pl. 95, fig. 8

Not Spinipora echinata: Hickson & England 1909: 352 , pl. 44, fig. 8

Errina echinata: Boschma 1964: 293 , 298; Boschma 1957: 53; Boschma & Lowe 1969: 15, pl. 5, map 2; Broch 1951b: 125– 126; Zamponi 2008: 188, 198, fig. 9

Errina (Inferiolabiata) echinata: Boschma 1956 : F102–F103, figs. 84, 1b–c; Boschma 1964: 294; Cairns 1983a: 107–109, figs. 22b–c, 24a–h, 25a–b, map 7; Río Iglesias et al. 2012: 191

Stellapora echinata: Cairns 1983b: 428 , table 1, 454–455, figs. 9a–i, 25i; Cairns & Macintryre 1992: 98, table 1; Bax & Cairns 2014: 108–110, table 1, map 4

Distribution. Off Mar del Plata, 1097 m; Patagonia, 42 S to 48 S; Burdwood Bank, 357–1647 m. New record off Mar del Plata, 1144–1289 m.

Material examined. USNM 59945 off Burdwood Bank , Eltanin St. 1593 (54° 43–42’ S, 56° 37–39’ W); MACN-In 40657 off Mar del Plata, Argentina, St. 36 (37º 57.508’ S, 54º 23.989’ W), 1289 m, May 2013 ; MACN-In 42511 off Mar del Plata , Argentina, St. 35 (37º 54.045’ S, 54º 24.091’ W), 1245 m, May 2013 ; MACN-In 42512 off Mar del Plata , Argentina, St. 12 (37º 57.907’ S, 54º 31.921’ W), 1144 m, August 2012 .

Description. Colonies robust and large ( Fig. 18 ). Branches thick, blunt-tipped and very close to each other, sometimes anastomosing. Growth mainly uniplanar. Branches round to slightly elliptical in cross section, with larger axis generally parallel to plane of growth. Largest basal branch measured 2.2 x 1.8 cm wide, attached to dead specimen of Bathelia candida by expansive base.

Coenosteum white and prickly. Microtexture granular to imbricate in some sections. Granules irregularlyshaped, sometimes pyramidal. Coenosteal strips poorly defined. Ocassionally short, straight and shallow slits are present, perforated by one or two pores 22–55 µm wide aligned within them ( Fig. 19f ). In these cases the width of a strip delimited by two parallel slits may be measured (around 0.1 mm). These pores are also present in a random distribution on coenosteum surface ( Fig. 19g ).

Gastropores and dactylopores abundant, distributed uniformly on coenosteal surface, although less abundant on posterior side. Gastropores 0.33–0.61 mm wide (average 0.48 mm, n=45, σ=0.07) and of two types: round and stellate ( Fig. 19g ). Stellate gastropores similar to cyclosystems, but lack dactylopore in each groove. These grooves, unlike dactylopores, are only present at surface opening of gastropore and do not extend downwards into gastropore tube. Up to four grooves were counted in stellate gastropores. Gastropore tubes short and peripheral. Gastrostyles needle-shaped (H:W up to 5.5), 0.9–1.0 mm tall and almost reach coenosteal surface ( Fig. 19a ). They bear longitudinal ridges of cylindrical to conical spines fused with each other. Ridges in gastrostyle base lack spines ( Fig. 19b ).

Dactylopores of two kinds ( Fig. 19c ): a longitudinal slit on a tall U-shaped spine ( Fig. 19d ) and a round pore slightly raised from coenosteal surface. U-shaped dactylopore spines bear thin transluscent walls that extend laterally like lamella, surpassing dactylotome limits. They may reach 2.4 mm high. Three to four spines adjacent to round gastropore often fuse laterally, forming a translucent sheet up to 3.7 mm wide, where dactylotome limits are still noticeable ( Fig. 19e ). Dactylotomes 0.13–0.20 mm wide, and round dactylopores around 0.1 mm in diameter. Most U-shaped dactylopore spines abcauline. In stellate gastropores septa often extend upwards, which suggests them being precursors of dactylopore spines.

Ampullae spherical and conspicuous on coenosteal surface, some slightly sunken. External and internal diameter up to 1.4 mm ( Fig. 19c ) and 1.1 mm ( Fig. 19a ), respectively. Judging by size of ampullae, the described specimens are probably female.

Discussion. Stellapora echinata was originally described by Moseley (1879) as Spinipora echinata based on a specimen from station n 320 of the Challenger expedition, off Mar del Plata. Hickson (1912) placed this species within the genus Errina due to the presence of U-shaped dactylopore spines and the genus Spinipora Moseley, 1879 became a subgroup ( Spinipora group) within Errina . Hickson and England (1909) described a specimen from the Indian Ocean which, according to Boschma (1964) and Cairns (1983a), is an incorrect identification. Broch (1951b) proposed to eliminate the Spinipora category, divided the genus Errina in two subgenera: Eu-Errina and Inferiolabiata , and suggested including Errina echinata in the latter, due to the abcauline orientation of most of the spines. Boschma 1956 also proposed fusing the category Spinipora with the subgenus Inferiolabiata , which included all species within the genus Errina that bore abcauline spines. Cairns (1983a) described specimens from Burdwood Bank, establishing the second record of this species since Moseley (1879). Cairns (1983b), in his revision of Stylasteridae genera, discarded the subgenus Inferiolabiata and arranged the species within this group in three genera: Inferiolabiata , Lepidotheca and Stellapora , S. echinata hitherto being the only known species of the latter. Río Iglesias et al. (2012) reported the third record of S. echinata based on the identification of specimens from Patagonia, from 42° S to 48° S within a depth range of 200–1500 m (specific depth not informed).

The studied specimens differ with those described by Cairns (1983a) in the amount of grooves in stellate gastropores. Those here described bear up to four grooves whereas those described by Cairns (1983a) bear up to seven. This difference is probably intraspecific variability. The present work provides the fourth record of this species.

Figures

FIGURE 18. Colony of Stellapora echinata.

FIGURE 19. Stellapora echinata. (a) Branch cross section revealing gastrostyles, dactylopore spines and ampullae cavities. (b) Gastrostyles. (c) Surface of colony displaying flush gastropores, slightly raised dactylopores, dactylopore spines and ampullae. (d) Longitudinal slit on dactylopore spine. (e) Laterally-fused dactylopore spines forming transluscent lamella. (f) Coenosteal pores and perforated slits. (g) Stellate gastropores, coenosteal pores and flush/slightly raised dactylopores.