Eleutheria dichotoma Quatrefages, 1842

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 : 49-51

Eleutheria dichotoma Quatrefages, 1842

Fig. 33 A, B

See Schuchert (2006) for a complete synonymy.

Material examined. HCUS-S 038p and HCUS-S 038m (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp and medusa stages.

Description (based on our own observations; Brinckmann-Voss 1970; Schuchert 2006, 2012):

Hydroid. Colonies stolonal, small; hydrorhiza as creeping, unbranched or slightly branched tubes, covered by smooth and delicate perisarc extending to base of hydranth; hydrocaulus absent or rudimentary; hydranth cylindrical, very extensile; hypostome large, rounded-conical, with glandular perioral cavity at apex; with up to 10 capitate oral tentacles in one whorl; medusae buds in lowest part of hydranth, either singly or in clusters borne on short branching, or not, gonostyle, carrying up to four medusa buds. Colours: hydranth with pink or white gastrodermis, depending on food.

Medusa. Adult. Umbrella flatter than hemispherical, 0.3 mm high, 0.5 mm wide; manubrium cylindrical to conical, extending slightly beyond umbrella margin; usually 6 radial canals; gonads in specialized umbrellar brood pouches situated above manubrium; with a thick marginal cnidocyst ring; up to 14 solid marginal tentacles, usually 5–6, not corresponding to the radial canals, bifurcated in lower, unarmed, branch with an adhesive disk and upper branch with a single cnidocyst knob; with one abaxial ocellus on each tentacular base; medusa buds on exumbrellar side of circular canal. Colours: body olive-cream, ocelli red to brown.

Developmental stages. Detailed descriptions are reported by Schierwater (1989).

Cnidome. Stenoteles of two size classes (polyp); stenoteles and desmonemes (medusa).

Habitat type. Medusa frequents small rocky pools in the tidal regions on weeds (depth range: 0–20 m) (see Schuchert 2006).

Substrate. Preferably on Ulva , but also Gigartina and Cystoseira (algae), Posidonia leaves.

Seasonality. In the Mediterranean Sea, Eleutheria dichotoma occurs from March to October (for a review see Bouillon et al. 2004).

Reproductive period. In the Tyrrhenian Sea, fertile colonies occur from February to March (Brinckmann- Voss 1970); along the Mediterranean French coast in August ( Galea 2007).

Distribution. Atlantic, Pacific, Mediterranean, Black Sea ( Thiel 1935; Kramp & Damas 1925; Teissier 1965; Medel & López-González 1996; Brinckmann-Voss 1970; Bouillon et al. 2004; Fraser et al. 2006; Schuchert 2006; Gravili et al. 2008a).

Records in Salento. Rare at: Porto Cesareo, S.ta Caterina, Costa Merlata (Ionian and Adriatic Apulian coast), ( Miglietta et al. 2000; Gravili 2006; Gravili et al. 2008a).

Remarks. The whole life cycle was examined in the present study. The polyp has been found in nature a few times (see Schuchert 2006). Eleutheria dichotoma medusae are a favourite subject for numerous studies due to easy rearing ( Hartlaub 1886; Lengerich 1923a, b).

References. Lo Bianco (1909), Mayer (1910), Russell (1953), Picard (1958a), Kramp (1959, 1961), Rossi (1971), Medel & López-González (1996), Miglietta et al. (2000), Bouillon et al. (2004), Gravili (2006), Schuchert (2006, 2012), Galea (2007), Gravili et al. (2008a).

Figures

FIGURE 33. Eleutheria dichotoma: A, hydranths developing medusa buds; B, medusa with buds (drawn by C. G. Di Camillo). Scale bars: A, 1.0 mm; B, 0.5 mm.