Stylaster profundus ( 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 : 40-42

Stylaster profundus ( Moseley, 1879)

( Figs. 23 , 24 )

Allopora profunda Moseley 1879: 454–457 , pl. 34, fig. 6, pl. 35, fig. 13, pl. 39, pl. 44, fig. 12; Moseley 1881: 62–65, pl. 1, fig. 6, pl. 2, fig. 13, pl. 6, pl. 11, fig. 12; Boschma 1957: 27; Cairns 1983a: 142–143, figs. 41b, 44a–f, 45a–c, map 14

Stylaster (Allopora) profundus: Boschma 1951: 457

Stylaster profundus: Hickson & England 1905: 8 ; Cairns 2011: 3, fig. 2c, 9, fig. 7e; Bax & Cairns 2014: 108–110, table 1, map 4

Distribution. SWA off Argentina near Río de la Plata; South Georgia; Southwestern Chile. Depth: 631–1097 m. New record off Mar del Plata, 877–1398 m.

Material examined. USNM 62571 off South Georgia, Eltanin St. 1536 (54° 29–31’ S, 39° 22–19’ W); MACN- In 40642 off Mar del Plata, Argentina, St. 42 (37° 59.110’ S, 54° 41.136’ W), 877 m, May 2013 ; MACN-In 42490 off Mar del Plata , Argentina, St. 36 (37° 57.508’ S, 54° 23.989’ W), 1289 m, May 2013 ; MACN-In 42491 off Mar del Plata , Argentina, St. 59 (37° 49.688’ S, 54° 5.236’ W), 1398 m, September 2013 .

Description. Specimens belong to Group A, given the arrangement of cyclosystems on lateral and anterior face of branches. Some cyclosystems may be present on posterior face as well. Branching dichotomous, without anastomosis, except where a polychaete tube is present. Colonies robust and mainly uniplanar. Branches round to slightly ovoid in cross section, with larger axis perpendicular to plane of fan. Branches bearing a polychaete tube flatten so that larger axis is parallel to plane of growth. Largest specimen measured is 6 cm wide and 6 cm tall, with basal branch 7 mm wide. Colonies grow attached to dead specimens of Bathelia candida or small rocks through an expansive base. Thinnest branches may measure down to 2 mm. Reduction in diameter from main to terminal branches is gradual. Polychaete tube may develop along anterior or posterior face of branches. Its surface is smooth, bearing lateral openings through which worm is visible ( Fig. 23 ).

Coenosteum white, smooth and porcellaneous, with a reticulate-granular microtexture. Coenosteal strips 71– 114 µm wide, delimited by curved, more or less continuous slits. Within slits there are deeper zones, possibly deep pores. Granules within coenosteal strips are clustered and irregularly-shaped ( Fig. 24c ). In some zones of the colony granules are less defined, strips are flatter, and slits are reduced to their deeper zones.

Cyclosystems round, elliptical or irregularly shaped, especially in branch axils. They are 1.2–2.8 mm wide (average 2.0 mm, n=50, σ=0.3). Gastropores round to slightly oval, 0.80–2.00 mm wide (average 1.19 mm, n=50; σ=0.22). Cyclosystems either flush or slightly raised, possibly originating a new branch. Number of dactylotomes per cyclosystem 9–19 (mode 13, n=50). They are 91–208 µm in diameter. Pseudosepta variable in width and occupy about 1/10 of total gastropore tube height. Basal and flush cyclosystems tend to bear less dactylotomes, but diastema is generally absent. Instead, a lone dactylopore may be present behind or on a pseudoseptum, possibly the case of a vestigial dactylotome ( Fig. 24b ).

Dactylostyle rudimentary, made up of one or two more or less adjacent rows of cylindrical rods, and extends towards depths of dactylopore tube. Rods up to 46 µm tall and 14 µm thick ( Fig. 24d ) and dactylostyle around 64 µm wide.

Gastropore tube long and mainly straight, lacking ring palisade ( Fig. 24a ). Gastrostyle robust, conical and flattened in antero-posterior direction ( Fig. 24e, f ). It occupies 1/4–1/5 of total gastropore tube hight and is covered uniformly in robust spines that fuse with each other forming multi-tipped lamella, similar to spine clusters in S. densicaulis gastrostyles.

Ampullae ovoid in shape and mainly internal, sometimes protruding slightly as hemispherical bumps. They are 0.8–1.0 mm in maximum internal diameter (n=5) and efferent pore is 0.4–0.5 mm wide, placed on gastropore tube wall as a circular depression ( Fig. 24a, f ). Two or more efferent pores may lead to the same gastropore tube ( Fig. 24f ). Given the size of ampullae and efferent pores, this is possibly the case of a female specimen (specimen MACN-In 40642).

Discussion. Stylaster profundus was originally described by Moseley (1879) as Allopora profunda , based on a specimen from station 320 of the Challenger expedition, off Mar del Plata. Cairns (1983a) examined specimens from stations 320 and 306 of the Challenger expedition and concluded that Moseley´s description from 1879 and 1881 corresponds with a specimen from station 306 in Golfo de Peñas, Chile. Therefore, the specimen from station 320 became a lectotype and the one from station 306, a paralectotype. Cairns (1983a) also examined specimens from South Georgia islands, establishing the second record of this species. Cairns (1983b) analysed genera Stylaster and Allopora Ehrenberg, 1834 and synonymised them, using Stylaster as the valid name for the genus. He created three subgroups within this genus, with main differences between them based on the arrangement of cyclosystems: Group A, which includes species previously belonging to Allopora , with cyclosystems on all surfaces of branches; Group C, which includes species belonging to Stylaster before this group was synonymised with Allopora , with cyclosystems exclusively arranged on laterals of branches; and Group B, which includes species with an intermediate arrangement between Group A and Group C.

To the description of S. profundus done by Cairns (1983a) we add further information about female ampullae, since hitherto the efferent pore had not been described. As regards the dactylostyle rods, their length is lower than the one informed by Cairns (1983a). It is probably necessary to examine more material in order to decide if this difference is significant. The specimens here described establish the third record of this species.

Figures

FIGURE 23. Stylaster profundus fragments (specimen at the right bears polychaete and is attached to fragment of unknown species).

FIGURE 24. Stylaster profundus. (a) Gastrostyle and gastropore tube bearing efferent pore on wall. (b) Cyclosystem and vestigial dactylotomes. (c) Reticulate-granular coenosteal texture. (d) Dactilostyle. (e) Gastrostyle. (f) Female ampullae cavities adjacent to gastropore tubes; efferent pore on gastropore tube wall.