Stegopoma giganteum Ramil & Vervoort, 1992

Gil, Marta & Ramil, Fran, 2021, Hydroids (Cnidaria, Hydrozoa) from the Vema and Valdivia seamounts (SE Atlantic), European Journal of Taxonomy 758, pp. 49-96 : 60-61

Stegopoma giganteum Ramil & Vervoort, 1992

Fig. 3D–E ; Table 3

Stegopoma giganteum Ramil & Vervoort, 1992: 36–38 , fig. 5e–f.

Material examined

SOUTH ATLANTIC OCEAN • 5 colonies, up to 15 mm high (1 growing on Zygophylax sp. , 1 on bivalve shell, 1 on ghost fishing net with a gonotheca); Valdivia Seamount , stn BT12; 24°49′01″–24°47′38″ S, 6°24′40″–6°25′26″ E; 887– 886 m depth; 7 Feb. 2015; SEAFO-2015 leg.; SEAFO-2015-40222 , SEAFO-2015-40612 , SEAFO-2015-40811 , SEAFO-2015-40827 , SEAFO-2015-40852 , LZM-UV slide R. 587 .

Description

Colony composed of a thin and ramified stolon, growing attached on the hydrocaulus and branches of Zygophylax sp. , from which arise pedicellate hydrothecae and gonothecae. Hydrothecae placed at the end of long, slender, smooth-walled and unbranched pedicels with some transversal scars due to regeneration after damage. Hydrothecae large, tubular, with smooth walls, almost bilaterally symmetrical, and slightly widening distally ( Fig. 3D ). Aperture closed by a triangular operculum adopting the shape of a gabled roof, formed by two opposite, semicircular sections on the distal part of the hydrothecal wall; opercular apparatus provided with longitudinal strips running downwards from top to basis. Hydranths are damaged or absent, and their description is not possible, but we can confirm that they are attached to the inner side of the hydrothecal base by means of a hyaline membranous ring, identical to the description given by Ramil & Vervoort (1992); this membranous ring indicates the boundary between the pedicel and the hydrotheca.

The gonotheca shows similar morphology to that described for the hydrotheca, including the closing apparatus, but it is supported by a shorter pedicel ( Fig. 3E ).

Remarks

This is the first record of S. giganteum after its original description. The large size of the hydrothecae (2–3 mm long), with long and narrow pedicels, are distinctive features of this species. In addition, the opercular apparatus, the presence of a hyaline membranous ring at the attachment site of the hydranth to the hydrothecal base, and the gonothecal shape fit well with the original description of this species. Consequently, despite the wide geographical distance between the type locality and the present record, we include this material in S. giganteum .

Distribution

This species is only known from off Cape São Vicente ( Portugal; type locality) where it was collected at a depth of 1523 m ( Ramil & Vervoort 1992). This is the first record for the South Atlantic.

Figures

Fig. 3. A–C. Zygophylax sp. A. Colony. B. Distal part of colony with hydrocladia. C. Part of hydrocladia with two hydrothecae. — D–E. Stegopoma giganteum Ramil & Vervoort, 1992. D. Hydrotheca on pedicel. E. Gonotheca. — F. Campanulina denticulata Clarke, 1907, part of colony ramified with hydrothecae. — G–H. Campanularia africana Stechow, 1923, detail of hydrotheca, lateral view.