Eutima gracilis (Forbes & Goodsir, 1851)

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 : 87-88

Eutima gracilis (Forbes & Goodsir, 1851)

Fig. 60 A, B

See Kramp (1961) and Russell (1953, 1970a) for a complete synonymy.

Material examined. HCUS-S 0 67 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp stage.

Description (after Russell 1953; Cornelius 1995):

Hydroid. Hydranths of Campanulina type, cylindrical, long, with blue pigment granules just below tentacle whorl; about 28 tentacles in a single whorl united by a large membranous basal web; hydrothecae lacking or strongly reduced; gonothecae cylindrical, with truncate end, long, containing up to 8 developing medusae.

Habitat type and substrate. Sedimentary environment (depth range 0–15 m), on Chaetomorpha linum (alga), sediment/ Ruppia (Barangé & Gili 1987) .

Seasonality. February, April–December in the Mediterranean Sea (Bouillon et al. 2004; Moscatello et al. 2004; De Vito 2006).

Reproductive period. Unknow in the Mediterranean Sea.

Medusa. Adult. Umbrella almost hemispherical when fully grown, up to 13 mm wide (exceptionally to 30 mm), mesoglea thick, watchglass-like; manubrium cross-shaped in transverse section, short, mounted on extremely long, narrow gastric peduncle extending far beyond bell margin and with small conical base; mouth with 4 small, simple lips; 4 straight radial canals and circular canal narrow; 4 gonads, same in colour as manubrium, restricted to portion of gastric peduncle, extending almost from base of peduncle to manubrium; velum fairly narrow; marginal bulbs not distinct; 2–4 (sometimes more) long perradial marginal tentacles; 40–80 or more marginal warts with fine black pigment granules; usually one lateral cirrus on each side of every tentacle and wart; 8 statocysts. Colours: mesoglea usually highly transparent, but colouration possibly due to local diet; manubrium pale pink or greenish.

Developmental stages. Umbrella high and bell-shaped when young, expanding laterally to become just flatter than hemispherical when fully grown, the smallest described stage is only 0.5 mm in height; manubrium short and no peduncle; mouth with 4 small lips; 4 radial canals and ring canal narrow; no signs of gonads; 2 opposite perradial marginal bulbs or swellings, one of which with a short lateral cirrus; 4 interradial and 8 adradial bulbs or swellings without lateral cirri; 8 marginal vesicles situated adradially, each with a single concretion (for more details about developmental stages of this species see Russell 1953).

Cnidome. Atrichous, basitrichous, and merotrichous isorhizas; sometimes microbasic mastigophores.

Distribution. Atlantic, Indo-Pacific?, Mediterranean ( Russell 1953, 1963; Fraser 1972; Cornelius 1995; Medel & López-González 1996; Bouillon et al. 2004; Moscatello et al. 2004; Gravili et al. 2008a; Touzri et al. 2010).

Records in Salento. Rare in the Salento Peninsula ( Moscatello et al. 2004; De Vito (2006).

Remarks. Only the medusa stage was seen in the present study. The hydroid is not known from nature, it was reared by Werner and illustrated by Russell (1970a). During swimming, the few long tentacles and the long gastric peduncle of the medusa wave together ( Russell 1953).

References. Babnik (1948), Russell (1949, 1953, 1970a), Kramp (1961), Benović (1973), Schmidt & Benović (1979), Benović & Bender (1987), Goy et al. (1988, 1990, 1991), Gili et al. (1991), Cornelius (1995), Benović & Lučić (1996), Medel & López-González (1996), Bouillon et al. (2004), Moscatello et al. (2004), De Vito (2006), Gravili et al. (2008a), Touzri et al. (2010).

Figures

FIGURE 60. Eutima gracilis: A, hydranth with gonangium; B, adult medusa (redrawn and modified: A after Russell 1970, B after Russell 1953 by A. Gennari). Scale bars: A, magnification unknown; B, 6.0 mm.