Rhizogeton nudus Broch, 1910

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 : 41-42

Rhizogeton nudus Broch, 1910

Fig. 27 A–C

See Schuchert (2004) for a complete synonymy.

Material examined. HCUS-S 0 32 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula).

Description (based on our own observations; Calder 1988; Schuchert 2004, 2012):

Hydroid. Hydrorhiza as creeping, slightly ramified stolons; colonies stolonal; hydranths sessile, with elongated and isodiametric column, up to 2–5 mm in height, with a short collar of very thin perisarc; hypostome dome-shaped; with 14–19 filiform tentacles, scattered over distal half or distal third of hydranth body. Gonophores as fixed sporosacs with spadix, on short, perisarc-covered pedicels borne on stolons; dimorphic, males oblong ellipsoid, females ovoid to fusiform, with 3– 5 eggs and embryos developing while sticking to spadix. Colour: hydranths pinkish.

Cnidome. Microbasic euryteles and desmonemes.

Habitat type and substrate. Grows on a variety of substrates (algae, Posidonia , mussels, hydroids, barnacles, bryozoans), depth range 0–100 m ( Boero 1981a, b; Boero & Fresi 1986; Faucci & Boero 2000; Fraschetti et al. 2002 all as Clava multicornis ).

Seasonality. In the Ligurian Sea ( Boero & Fresi 1986) in November; in Salento waters (De Vito 2006; this study), from March to November.

Reproductive period. Unknown in the Mediterranean Sea.

Distribution. Arctic and North Atlantic waters ( Broch 1910; Dons 1912; Kramp 1914; Calder 1972; Antsulevich & Polteva 1986; Jones 1992; Schuchert 2001a, 2004), Mediterranean ( Gravili et al. 2008a).

Records in Salento. Rare at: Porto Cesareo ( Faucci & Boero 2000; Andreano 2007); Costa Merlata ( Fraschetti et al. 2002); Torre Lapillo, Torre dell’Inserraglio, S.ta Caterina ( Andreano 2007); Otranto ( Andreano 2007; De Vito 2006; Gravili 2006; Gravili et al. 2008a; this study).

Remarks. This species is rather inconspicuous and rare, it has been misidentified as Clava multicornis by Boero (1981a, b), Boero and Fresi (1986). R. nudus was previously considered as restricted to arctic and cooltemperate waters of the North Atlantic ( Schuchert 2004); the finding at both Portofino and Otranto (at the longitudinal extremes of the Italian Peninsula) suggests that this species might be distributed along almost the whole Italian coast, on rocky shores with barnacle belts.

References. Sarà et al. (1978), Boero (1981a, b), Boero & Fresi (1986), Faucci & Boero (2000), and Fraschetti et al. (2002) as Clava multicornis ; Schuchert (2004, 2012), De Vito (2006), Gravili (2006), Gravili et al. (2008a).

Figures

FIGURE 27. Rhizogeton nudus: A, colony; B, female sporosacs; C, young male sporosac, same scale as B (A drawn by C. G. Di Camillo; B, C redrawn and modified after Schuchert 2004 by A. Gennari). Scale bars: A, 1.0 mm; B, C, 0.5 mm.