Cladonema radiatum Dujardin 1843

Cladonema radiatum Dujardin, 1843

Fig. 32 A, B

See Schuchert (2006) for a complete synonymy.

Material examined. HCUS-S 037p and HCUS-S 037m (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp and medusa stages.

Description (based on our own observations; Brinckmann & Petersen 1960; Schuchert 2006, 2012):

Hydroid. Hydrorhiza as creeping ramified stolons; colonies stolonal or slightly branching; hydrocaulus of variable length, usually longer than hydranth, covered by smooth perisarc terminating shortly below hydranth; hydranths clavate, terminal; hypostome rounded, with apical ectoderm presenting a well developed glandular perioral cavity; with one whorl of 4–5 capitate oral tentacles and one whorl of 4–5 filiform aboral tentacles with a slight terminal swelling; medusa buds naked, borne singly on hydranth just above filiform tentacles.

Habitat type. Hydroid and medusa occur in shallow water and in tide pools on Posidonia, algae and other hard substrata (depth range 0–50 m) (Picard 1952; Rossi 1971; Morri & Bianchi 1976; Barangé & Gili 1987; Faucci & Boero 2000).

Substrate. Cymodocea nodosa and Posidonia leaves, Ruppia, algae such as Cystoseira, Cardium edule.

Seasonality. In the western Mediterranean Sea, in May–August (Motz-Kossowska 1905; Brinckmann-Voss 1970); November (Boero & Fresi 1986).

Reproductive period. In the western Mediterranean Sea, fertile colonies occur from June to August, rarely also in October (Motz-Kossowska 1905); May–July (Brinckmann-Voss 1970).

Medusa.

Adult. Umbrella bell-shaped, slightly higher than broad, about 3 mm wide and 4 mm high when mature, mesoglea moderately thin, sometimes with a slight apical projection; manubrium fusiform, not extending beyond umbrella margin, with usually 5, sometimes 4, perradial pouch-like outgrowths in its middle region; mouth with usually 5, sometimes 4, short protuberances or lobes, each armed with cnidocyst clusters; usually 5, sometimes 4, thin primary radial canals some of which bifurcate to form 10, sometimes 8, radial canals in all; circular canal narrow; gonads on the upper two-thirds of manubrium and on the perradial pouches; velum rather broad; usually 10, sometimes 8, marginal tentacles, corresponding to the number of radial canals, branched, with elongated thickened bases from the underside of which grow 1 to 4 (up to 10) branches with adhesive organs, the branched upper portions of the marginal tentacles are beset with numerous cnidocyst clusters; with an abaxial ocellus at the base of each marginal tentacle. Colours: black or deep crimson ocelli, manubrium and marginal tentacles red, bright-red or brown.

Developmental stages. Newly released medusa with 8–10 bifid tentacles, upper branch with a terminal nematocyst cluster and a few oral clusters.

Cnidome. Stenoteles and mastigophores (hydroid); stenoteles, desmonemes (medusa).

Distribution. Atlantic, Indo-Pacific, Black Sea, Mediterranean (Thiel 1935; Russell 1953; Kramp 1959; Calder 1988; Medel & López-González 1996; Brinckmann-Voss 1970; Boero & Fresi 1986; Benović & Lučić 1996; Migotto 1996; Schuchert 1996, 2006; Bouillon et al. 2004; Gravili et al. 2008a).

Records in Salento. Rare in the following localities: La Strea, Porto Cesareo (Faucci & Boero 2000; Miglietta et al. 2000); Grotta del Ciolo (Denitto et al. 2007); Otranto (De Vito 2006; Gravili 2006; Gravili et al. 2008a; this study).

Remarks. The whole life cycle was examined in the present study. The medusa of Cladonema radiatum is rather variable with respect to the branching patterns of the radial canals and their number. There are several nominal Cladonema species with minimal or poorly clarified differences (Kramp 1968; Stepanjants et al. 1993; Schuchert 2006). Another species referable to this genus has been found both in Ligurian and Salento waters (unpublished), it lives in horny sponges, sticking out from their oscula, and can completely retract into the host body. It is probable that, due to this particular association, the species is distinct from Cladonema radiatum, even though the morphology is identical. The medusa has not been observed yet, so the taxonomic position is uncertain.

References. Hartlaub (1907), Mayer (1910), Hadzi (1911), Leloup (1934), Russell (1953), Picard (1952, 1958a), Trégouboff & Rose (1957), Kramp (1959, 1961), Brinckmann-Voss (1970, 1987), Rossi (1971), Goy (1973), Morri & Bianchi (1976), Boero & Fresi (1986), Barangé & Gili (1987), Riedl (1991), Benović & Lučić (1996), Medel & López-González (1996), Schuchert (1996, 2006, 2012), Migotto (1996), Faucci & Boero (2000), Miglietta et al. (2000), Bouillon et al. (2004), De Vito (2006), Gravili (2006), Denitto et al. (2007), Gravili et al. (2008a).