Sertularella microtheca Leloup, 1974

Horia R. Galea, Dirk Schories, Verena Häussermann & Günter Försterra, 2017, Taxonomic revision of the genus Sertularella (Cnidaria: Hydrozoa) from southern South America and the subantarctic, with descriptions of five new species, Revue suisse de Zoologie 124 (2), pp. 255-321 : 291-292

Sertularella microtheca Leloup, 1974

Fig. 14F, G; Table 17

Sertularella microtheca Leloup, 1974: 30 , fig. 24.

Sertularella robusta . – p.p. Vervoort, 1972: 129, fig. 40B (non figs 40A, 41A = S. robusta Coughtrey, 1876 ). – p.p. El Beshbeeshy, 2011: 144, fig. 46E-H (non fig. 46A-D = S. robusta ) [non Sertularella robusta Coughtrey, 1876 ].

Material examined: HRG-1095; Chile, Región de Aysén, southeastern point of Canal Ultima Esperanza, -45.97608° -74.01133°, 23 m, coll. HSFS, HF21, lot #216; 10.04.2014; small colony composed of several sterile stems, up to 1 cm high.

Description: Stolonal hydrothecae or short (up to 1 cm high), erect, unbranched or sparingly-branched stems, arising from creeping, branching, filiform hydrorhiza. Stems and, when present, side branches divided into up to 10 exceedingly long, slender, geniculate internodes by means of indistinct, oblique constrictions of the perisarc; the latter relatively thick throughout the colony; side branches borne on short stem apophyses arising from below a hydrothecal base, apophyses displaced towards one side of the stem, not laterally and, consequently, not in the same plane; 1 st internode of a side branch comparatively longer than subsequent ones; remainder of branch with same structure as the stem; no further branching observed. A hydrotheca confined to the distal end of each internode; fusiform, adnate for ca. 1/4th its length, transversely-ridged (generally 4, occasionally 5 ridges present), distally a short, smooth neck region; aperture with 4 pointed, triangular cusps separated by rather deep, semicircular embayments; 3 large, lamellar, submarginal, internal projections of perisarc (2 latero-adaxial, 1 abaxial); a 4-flapped operculum. Gonotheca stolonal, barrelshaped, transversely ridged (with ca. 6 ridges), distally a neck region bearing apically an aperture surrounded by 4 spines.

Dimensions: See Table 17.

Remarks: The present material is composed of erect stems only, while Leloup (1974) reported the co-occurrence of stolonal hydrothecae within colonies otherwise comprising erect stems.

This species shows striking resemblances to S. robusta Coughtrey, 1876 , a species with which it has been synonymized earlier (e.g. El Beshbeeshy, 2011; Galea, 2007). When colonies of both are examined side by side, obvious differences arise, such as: proportionally longer and much slender internodes, as well as smaller and much slender hydrothecae in S. microtheca .

Distribution: Chile – Región de los Lagos [Canal Calbuco ( Leloup, 1974)]; Región de Aysén [Canal Ultima Esperanza (present study)]. Argentina – Provincia de Santa Cruz [off Deseado (p.p. Vervoort, 1972, as S. robusta )].