Eirene viridula (Péron and Lesueur, 1810), Peron and Lesueur, 1810

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 : 84-86

Eirene viridula (Péron and Lesueur, 1810)

Fig. 58 A, B

See Kramp (1961) for a complete synonymy.

Material examined. HCUS-S 0 65 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp stage.

Description (after Metschnikoff 1886a; Russell 1953; Cornelius 1995):

Hydroid. Hydrorhiza as branching or anastomosing stolons; colonies erect; hydrocauli short, with perisarc smooth to sinuous throughout; hydranths of Campanopsis type, with cylindrical body tapering slightly basally, ca 5 on each hydrocaulus; hypostome conical-rounded; with about 10–24 amphicoronate oral filiform tentacles, intertentacular membranous basal web reported; hydrothecae reduced or lacking, depending on age; gonothecae oblong, round-truncated above and below, with thin walls, long, possibly dropping during medusa development, probably containing a single medusa bud each.

Habitat type. Depth range: 0.5– 3 m ( Faucci & Boero 2000).

Substrate. Cystoseira (brown alga).

Seasonality. February–December ( Faucci & Boero 2000; Galea 2007) in the Mediterranean Sea.

Reproductive period. April–May, June–October (Gili 1986) in the western Mediterranean.

Medusa. Adult. Umbrella hemispherical, up to 30 mm wide or even larger, mesoglea of middle portion fairly thick, thinner at sides; manubrium fairly short, small, mounted on an elongated and slender gastric peduncle reaching beyond exumbrellar margin; mouth with 4 very long pointed lips with crenulated margins; 4 radial canals and circular canal narrow; gonads linear, straight, slightly sinuous, limited to disk of subumbrella, extending from somewhat beyond base of peduncle almost to exumbrellar margin; velum narrow; about 70 or more conical marginal bulbs; each with one tentacle of different size, small and large alternating; with distinct excretory papillae; 50 or more statocysts. Colours: colourless except for greenish tinge on stomach.

Developmental stages. The first stage of E. viridula , after liberation from the hydroid, has not been observed. The youngest observed specimens have bell-shaped umbrella, 1.5 mm high and wide; manubrium short, without gastric peduncle; mouth with 4 distinct short lips; 4 narrow radial canals and ring canal; gonads not visible; 4 perradial marginal tentacles with rounded bases; 8 statocysts, one on either side of each marginal tentacle, each with one concretion. E. viridula medusa is already differentiated at a size of 2.0–2.5 mm by having a small peduncle. The gonads usually appear as elongated thickenings on the radial canals when the medusa is 3.5–4.0 mm in diameter (for more details about the medusa development see Russell 1953). Colours: brown pigment in the endoderm of the bases of the marginal tentacles, and also at the base of the stomach and extending interradially as far as the mouth.

Cnidome. Atrichous and basitrichous isorhizas (hydroid); atrichous isorhizas and microbasic mastigophores (medusa).

Distribution. Atlantic, Indo-Pacific, Mediterranean ( Russell 1953; Cornelius 1995; Medel & López-González 1996; Bouillon et al. 2004; Gravili et al. 2008a).

Records in Salento. Rare at La Strea, Porto Cesareo ( Faucci & Boero 2000).

Remarks. Perigonimus nudus Stechow, 1919 was recognized as a new synonym of Eirene viridula (Péron and Lesueur, 1810) by Schuchert (2007). In its earliest stages, the medusa of E. viridula bears a very close resemblance to that of Clytia hemisphaerica , but its gonads are more elongated and more proximally placed than in Clytia ( Russell 1953) . Gonothecae and medusae not seen in the present study.

References. Mayer (1910), Russell (1953), Trégouboff & Rose (1957), Picard (1958a), Anichini (1959), Rossi (1971), Goy (1973), Schmidt (1973), Benović (1977), Schmidt & Benović (1979), Dowidar (1984), Lakkis & Zeidane (1985), Castello i Tortella (1986), Gili (1986), Benović & Bender (1987), Goy et al. (1988, 1990, 1991), Benović & Lučić (1996), Medel & López-González (1996), Benović et al. (2000), Faucci & Boero (2000), Bouillon et al. (2004), Galea (2007), Gravili et al. (2008a).

Figures

FIGURE 58. Eirene viridula: A, hydroid stage with gonotheca; B, adult medusa (redrawn and modified: A after Cornelius 1995, B after Kramp 1968 by C. G. Di Camillo). Scale bars: A, 2.0 mm; B, 30 mm.