Stegolaria geniculata ( Allman, 1888 )

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 : 10-11

Stegolaria geniculata ( Allman, 1888)

( Fig. 4C–F )

Stegolaria geniculata — Watson & Vervoort, 2001: 154 –156, fig. 2a–d (synonymy); Vervoort, 2006: 220–221.

Material examined. 9752#1, three stems up to 95 mm high, no gonothecae; 9753#8, one strongly polysiphonic stem 67 mm high, no gonothecae.

Description. Strongly polysiphonic stems, up to 95 mm high. Branching irregular in more or less one plane. Stems and branches with distinct zigzag.

Hydrothecae alternately arranged in one plane. Hydrotheca tubiform ( Fig. 4C ), curved outwards, adnate to stem or branch for half to two-thirds of its height ( Fig. 4C ). With a basal circular diaphragm ( Fig. 4E ). Abcauline wall concave, free part of adcauline wall convex to nearly straight. Hydrothecal rim uneven, with two large cusps, separated by two large embayments ( Fig. 4C–D, F ). Operculum composed of two semi-circular, pleated valves, attached to rim embayments and closing as a roof.

Measurements (in µm). Hydrotheca: diameter at aperture 210–250, abcauline length 1300, free part of adcauline length 500–630, adnate part of adcauline length 800, adcauline length 1430, diameter at free/adnate transition 220, diameter at base 120, diameter at diaphragm 140.

Remarks. Millard (1977) believed Stegolaria operculata ( Nutting, 1906) to be conspecific with S. geniculata , considering that there is little to distinguish them. In her material, she found a variable geniculation, with some branches almost as geniculate as typical for S. geniculata , and others completely straight, as typical for S. operculata . Vervoort (1985) also indicated that both species are extremely similar and was inclined to consider them identical, although he postponed the decision. Ramil & Vervoort (1992), however, considered them conspecific, pointing out that the principal point of difference between the two species is the absence of distinct geniculation in S. operculata . Other authors have kept them separated ( Hirohito 1995, Vervoort & Watson 2003). Vervoort & Watson (2003) indicated that it is necessary to have more, and better preserved, fertile material to clarify the relationship between the two species and Vervoort (2006) pointed out that this issue is still open. The material studied here does not allow clarification of this question.

Ecology and distribution. This is a deep-water species ( Millard 1977), reported at depths from 253 ( Millard 1977) to 1727 m ( Calder & Vervoort 1998); the present material was collected at depths between 1007 and 1942 m from the Porcupine Seabight.

According to Vervoort (2006), Stegolaria geniculata is a fairly common deep water species in the Atlantic and, if its synonymy with S. operculata is assumed, also in the Pacific and Indian oceans.

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),