Stegopoma plicatile ( M. Sars, 1863 )

Peña Cantero, Álvaro L. & Horton, Tammy, 2017, Benthic hydroids (Cnidaria, Hydrozoa) from bathyal and abyssal depths of the Northeast Atlantic held in the modern Discovery Collections, Zootaxa 4347 (1), pp. 1-30 : 11-13

Stegopoma plicatile ( M. Sars, 1863)

( Fig. 4G–H )

Stegopoma plicatile —Schuchert, 2001: 51–53, fig. 37A–E (synonymy).

Material examined. 9752#1, several stems up to 60 mm high, on axis of dead gorgonian, basibiont of Zygophylax , no gonothecae; Stn CE14011-BIO 217, a fragmented colony (longest fragment, 105 mm long), no gonothecae.

Measurements (in µm). Hydrotheca: diameter at aperture 240–300, abcauline length 950, free part of adcauline length 50, adnate part of adcauline length 1000, adcauline length 1080, height, to the end of cusps 1200.

Remarks. This species is easily recognizable by the simultaneous presence of adnate and free hydrothecae. The adnate ones ( Fig. 4G ), alternately arranged in one plane, are tubiform, with the apical portion curved outwards. The free hydrothecae ( Fig. 4H ) are on short pedicels that originate on the opposite side of each adnate hydrotheca, by the middle of the adcauline wall.

See Schuchert (2001) for a recent discussion on its taxonomic history and Schuchert et al. (2017) for the identification of the medusa stage, which belongs to Ptychogena crocea Kramp & Dumas, 1925 , and a discussion on the validity of genus. Schuchert et al. (2017) also considered that S. plicatile is most probably a complex of cryptic species and taxonomically considered it as a partial synonym of P. crocea .

Ecology and distribution. Reported from depths between 15 and 1940 m (Schuchert 2001); present material from 982 to 1042 m.

Worldwide distribution ( Peña Cantero 2014). Schuchert (2001) considered this species as predominantly circumarctic, although he indicated that it is also known from New Zealand, Antarctica, far southern America and Philippines. Our material comes from the Porcupine Seabight and Rockall Bank.

Figures

FIGURE 4. Modeeria rotunda (Quoy & Gaimard, 1827): A, hydrotheca; B, basal part of hydrotheca showing diaphragm (arrow). Stegolaria geniculata (Allman, 1888): C, hydrotheca (note geniculate arrangement); D, hydrotheca showing plicate operculum; E, basal part of hydrotheca showing diaphragm (arrow); F, detail of distal part of hydrotheca. Stegopoma plicatile (M. Sars, 1863): G, adnate hydrotheca; H, free hydrotheca. Scale bars: Scale bars: 200 µm (A, C-D, G-H), 100 µm (B, E – F),