Obelia longissima (Pallas, 1766)

Gravili, Cinzia, Vito, Doris De, Camillo, Cristina Gioia Di, Martell, Luis, Piraino, Stefano & Boero, Ferdinando, 2015, The non-Siphonophoran Hydrozoa (Cnidaria) of Salento, Italy with notes on their life-cycles: an illustrated guide, Zootaxa 3908 (1), pp. 1-187 : 155-157

Obelia longissima (Pallas, 1766)

Fig. 110 A–D

See Schuchert (2001a) for a complete synonymy.

Material examined. HCUS-S 117 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp stage.

Description (based on our own observations; Cornelius 1995; Schuchert 2001a):

Hydroid. Hydrorhiza as a mass of stolons from which hydrocauli arise; colonies erect, long and flexuose, up to 40 cm high; hydrocauli monosiphonic, with lateral and alternate branches, may be polysiphonic and forked in older colonies, internodes usually nearly straight, thickened in older portions of stem, annulated basally; hydrocladia also flexuose, usually branched in two at their origin, internodes long, in zigzag, ringed basally and below hydrotheca; hydrotheca elongate, bell-shaped, perisarc very thin, diaphragm transverse to oblique, borne alternately at the end of each internode on pedicels with about 6–10 annuli, rim shallow castellated or with shallow rounded cusps, slightly flared. Colours: main stem dark; nodes (but not the internodes) dark in young branches; internodes pale when young, becoming darker after. Gonothecae inverted-conical, narrower basally, with a distal aperture on a short collar.

Cnidome. Fl-type isorhizas and A-type b-rhabdoids (microbasic b-mastigophores) ( Östman 1982, 1987, 1999).

Habitat type. Commonest subtidally, on both rocky and sandy bottoms ( Cornelius 1995).

Substrate. Algae, phanerogams, and inert substrates.

Seasonality. Winter and spring (this study).

Reproductive period. Spring (this study).

Medusa. Typical for the genus.

Distribution. Nearly cosmopolitan ( Broch 1918; Kramp 1938; Cornelius 1990, 1995; Medel & López- González 1996; Schuchert 2001a; Bouillon et al. 2004: Gravili et al. 2008a).

Records in Salento. Rare in the Gulf of Taranto (S. Piraino unpublished observations).

Remarks. For more details and the medusa see Cornelius (1995). O. longissima resembles O. dichotoma and both species have often been synonymized (for more details see Schuchert 2001a). Cnidome differences between the two species may be one of the most reliable ways of distingushing them ( Östman 1982, 1987, 1999). Medusae not seen in the present study.

References. Picard (1958a) as O. plana ; Riedl (1959, 1966); Morri & Bianchi (1982, 1983) as O. plana ; Ramil (1988), Altuna (1994), Cornelius (1995), Medel & López-González (1996), Piraino et al. (1999) as O. plana, Schuchert (2001a) , Bouillon et al. (2004), Gravili (2006), Gravili et al. (2008a).

Figures

FIGURE 110. Obelia longissima: A, aspect of a large colony; B, detail of a portion of branch; C, medusa; D, gonotheca (A, B redrawn and modified after Cornelius 1995 by C. G. Di Camillo; C drawn by F. Boero; D redrawn and modified after Cornelius 1995 by A. Gennari). Scale bars: A, 15.0 cm; B, C, D, 0.5 mm.