Eudendrium racemosum (Cavolini, 1785)

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 : 32-33

Eudendrium racemosum (Cavolini, 1785)

Fig. 20 A–E

See Schuchert (2008b) for a complete synonymy.

Material examined. HCUS-S 0 25 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula). Description (based on our own observations; Marques et al. 2000a; Schuchert 2008b, 2012):

Hydroid. Hydrorhiza rhizocaulomic; colonies erect, often quite regular, bushy to tree-like, up to 160 mm high; hydrocaulus basally polysiphonic, branched, perisarc annulated to variable extent, on origins of hydrocladia and at other irregular intervals, alternating with smooth regions; hydrocladia roughly alternate, not in the same plane; hydranth on basally-ringed pedicel; hypostome peduncled; 25–30 filiform tentacles in one whorl; with a characteristic digitiform and naked nematophore on the body of some hydranths; colonies dioecious. Gonophores as fixed sporosacs, on polyps with atrophied tentacles to a varying degree (those bearing mature gonophores totally atrophied), females with a bifid spadix not acuminate, fertilized eggs encapsulated and attached to perisarc of blastostyle pedicels; males with 3–4 chambers, sometimes with a terminal button, without dense nematocyst cluster. Colours: eggs in gonophores dark orange-red. Colours: perisarc brown in older parts to yellowish in younger ones, polyp whitish to light orange-pink.

Cnidome. Atrichous isorhizas (10.5x4 to 11 x4 µm) on hypostome, hydranth and hydrocauli; shaft invisible in undischarged cnidocysts; small heterotrichous microbasic euryteles (6x 4 to 7 x5 µm) on tentacles and ectoderm.

Habitat type. Typically shallow-water species ( Boero & Fresi, 1986), which reaches deeper levels by ‘climbing’ on other organisms showing a sharp tendency to “acrophily” ( Boero, 1984); it was been collected in marine caves ( Riedl 1959, 1966).

Substrate. Rocks, sponges, algae, hydroids, gorgonians, mollusc shells, cirripedes, Posidonia oceanica , hard substrate and detritus, bryozoans.

Seasonality. In the Mediterranean Sea, it is present throughout the year, but rare from December to February when it likely overwinters as a stolonal system (Bouillon et al. 2004; De Vito 2006; Schuchert 2008b; Puce et al. 2009; this study).

Reproductive period. Fertile, in the whole Mediterranean Sea, from March to December, but mainly in the summer (De Vito 2006; Schuchert 2008b; Puce et al. 2009; this study).

Distribution. Widely distributed in the Indo-Pacific ( Boero & Bouillon 1993), also present in the temperate and subtropical eastern Atlantic; cosmopolitan ( Marinopoulos 1992; Marques et al. 2000a; Bouillon et al. 2004; Gravili et al. 2008a; Schuchert 2008b).

Records in Salento. Common at Otranto (De Vito 2006; Gravili 2006; Gravili et al. 2008a; this study).

Remarks. E. racemosum is one of the most common and conspicuous hydroids of the Mediterranean.

References. Motz-Kossowska (1905), Palombi (1940), Rossi (1961, 1971), Repetto et al. (1977), Gili & Ros (1985), Watson (1985), Boero & Fresi (1986), Barangé et al. (1987), Llobet i Nadal (1987), Barangé (1988), Barangé & Gili (1988), Marinopoulos (1981, 1990, 1992), Riedl (1991), Sommer (1992), Medel & López- González (1996), Morri & Bianchi (1999), Piraino et al. (1999), Marques et al. (2000a, b), Peña Cantero & García Carrascosa (2002), Puce et al. (2002), Azzini et al. (2003), Bouillon et al. (2004), De Vito (2006), Gravili (2006), Gravili et al. (2008a), Schuchert (2008b, 2012), Morri et al. (2009), Puce et al. (2009), Di Camillo et al. (2012), Tazioli & Di Camillo (2013), Romagnoli et al. (2014).

Figures

FIGURE 20. Eudendrium racemosum: A, colony silhouette; B, hydranth with basal nematophore; C, male blastostyle; D, gonozooid with female sporosacs; E, discharged and undischarged capsule of microbasic euryteles and basitrichous isorhizas (C, D same scale bar) (A, B, C, D drawn by C. G. Di Camillo; E drawn by F. Boero). Scale bars: A, 10 mm; B, C, D, 0.5 mm; E, 10 µm.