Sertularella patagonica (d’Orbigny, 1842)

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 : 294-295

Sertularella patagonica (d’Orbigny, 1842)

Fig. 15 A-E; Table 20

Sertularia patagonica d’Orbigny, 1842 : pl. 11 figs 3-5; 1847: 25. – Hartlaub, 1905: 643, figs H4, J4. – Nutting, 1904: 81, pl. 16 fig. 3.

Sertularella striata Stechow, 1923b: 10 (syn. nov.). – Stechow, 1925: 470, fig. 30. – Millard, 1964: 47, fig. 15. – (?) Blanco, 1974: 44, figs 2-8. – Millard, 1975: 304, fig. 97E-F. – Genzano, 1990: 45, figs 11-12. – Blanco, 1994: 201. – Genzano & Zamponi, 2003: 308.

non Sertularella striata . – Gili et al., 1989: 104, fig. 29A.

Sertularella mogotesensis El Beshbeeshy, 2011: 20 [new name for both Blanco’s (1967, p. 115) record of Sertularella atlantica Stechow, 1920 and her 1974 record (p. 44) of Sertularella striata Stechow, 1923b ; nomen nudum].

Sertularella atlantica . – Blanco, 1967: 115, pl. 3 figs 8-12, pl. 4 figs 1-4 [non Sertularella atlantica Stechow, 1920: 21 , fig. 2A].

Description: Colonies composed of either stolonal hydrothecae or short (up to 11 mm high), erect shoots arising from sinuous, smooth-walled stolon. Cauli thick, monosiphonic, usually unbranched, occasionally sparingly branched (1-3 short, roughly alternate side branches), smooth or with a reduced number (up to 3-4) of basal wrinkles; divided into internodes of varied length, though generally short, by means of rather indistinct, oblique nodes slanting in alternate directions. Proximal end of internodes provided with a couple of spiral twists, distally a hydrotheca. Side branches, when present, arising laterally from below the base of a stem hydrotheca. The latter close to one another, fusiform, free from the corresponding internodes for more than half their adaxial length; walls with 6-8 transverse ridges encircling their whole surface; aperture provided with 4 short, triangular cusps separated by shallow embayments; no submarginal, intrathecal cusps; a 4-flapped operculum. Perisarc thick throughout the colonies. Gonothecae arising from below the hydrothecal bases, broadly ovoid, walls provided with ca. 10 transverse ridges on nearly the whole surface, apically 3-4 minute spines surrounding the aperture, female with acrocysts.

Dimensions: See Table 20.

Remarks: One of the original illustrations by d’Orbigny (1842, pl. 11 fig. 5) can be misleading when attempting to compare this species with contemporary records from the study area, as the hydrothecae are figured with a decidedly scaly appearance. However, a similar illustration was provided by Hincks (1868) for S. rugosa ( Linnaeus, 1758) , while recent and more accurate drawings (e.g. Cornelius, 1995; Schuchert, 2001) show a quite common condition of the hydrothecae, typical of a species with transversely ringed walls.

Type material of S. patagonica is likely lost, as no mention of it was made by Van Praët (1979) in his catalogue of the type specimens housed in the Muséum national d’Histoire naturelle of Paris, France.

The typically short internodes, twisted basally, and the transversely annulated hydrothecae emphasized by d’Orbigny (1847) are characters also noted in Blanco’s (1967, as S. atlantica Stechow, 1920 ) account, and it is therefore assumed that both hydroids are conspecific. The latter nominal species, however, originates from the northern hemisphere, and is probably a synonym of S. tenella ( Alder, 1857) ( Picard, 1956; Cornelius, 1995).

In a subsequent paper, Blanco (1974) considered her earlier record as conspecific with her newly-obtained material assignable to S. striata Stechow, 1923b . Finally, Blanco (1994) recognized S. striata as a synonym of S. patagonica but, curiously, kept the former as the valid binomen.

According to the accounts of both Stechow (1925) and Millard (1964), S. striata exhibits the same morphological characters as S. patagonica , and their respective measurements are highly concordant (see Table 20 herein). For this reason, both nominal species are considered here as coterminous, with d’Orbigny’s hydroid name having priority.

The Namibian and South African records by Gili et al. (1989) most probably do not belong here, owing to the large size of the hydrothecae in their material.

The morphological similarity between S. patagonica and S. rugosa Linnaeus, 1758 invoked by both Kirchenpauer (1884) and Hartlaub (1901) is only superficial, and resides in particular in the ringed condition of the hydrothecal wall. However, the hydrothecal aperture is conspicuously tilted downwards in the latter species ( Cornelius, 1995; Schuchert, 2001), thus differing from the illustrations provided by both d’Orbigny (1842) and Blanco (1967). In addition, both species are certainly distinct on the account of their very remote areas of occurrence.

Distribution: Argentina – Provincia de Buenos Aires [off Mar del Plata ( Blanco, 1967, as S. atlantica ; Genzano, 1990, as S. striata )]; Provincia de Río Negro [Ensenada de Ros (d’Orbigny, 1847); Barranca final ( Blanco, 1974; 1994, both as S. striata )]. Elsewhere – South Africa ( Stechow, 1923b; 1925; Millard, 1964; 1975).