Eudendrium merulum Watson, 1985 Fig. 18 A–E See Schuchert (2008b) for a complete synonymy. Material examined. HCUS-S 0 22 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula). Description (based on our own observations; Watson 1985; Bavestrello & Piraino 1991; Schuchert 2008b): Hydroid. Hydrorhiza tubular; colonies erect; hydrocauli monosiphonic, up to 20 mm high, unbranched or branched, perisarc roughly annulated basally up to the lowest hydrocladia; hydranths up to 15 per hydrocaulus, rarely more, small, with a distinct groove round the base below a ring of a few large cnidocysts; hypostome clubshaped; with approximately 24 tentacles; colonies dioecious. Gonophores as fixed sporosacs; males borne on lower stems in dense cluster up to 20 per blastostyle, blastostyles completely reduced with distinct neck connecting gonophore chambers, terminal nematocyst button with some large euryteles can be present in mature sporosacs; females borne thickly on lower parts of colonies, globular, fully reduced, up to 6 scattered on blastostyles, spadix unbranched during early ontogeny, shed when mature; eggs with thin pellicle, placed along axis of blastostyle. Colour: hydranths whitish. Cnidome. Microbasic euryteles of two sizes: small ones 7– 9 x 3.0 mm abundant on tentacles; large ones 16.5–25.0 x 8.0–13.3 mm, having a much ornamented shaft and present in the cnidocyst ring and on spadix of female gonophores. Habitat type. From intertidal (Marques et al. 2000a) to infralittoral (Bavestrello & Piraino 1991). Substrate. Barnacles, bryozoans, sponges, polychaete tubes, and other solid substrata. Seasonality. Present throughout the year in the Mediterranean Sea (Bouillon et al. 2004; Puce et al. 2009). Reproductive period. June, October in Salento waters (De Vito 2006; this study). Distribution. Circumtropical (see 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; Ventura 2011; this study), Apulian coast (Gravili et al. 2010), and La Strea (Porto Cesareo) (Ventura 2011). Remarks. E. merulum is part of the E. ramosum group, which comprises several species with large complementary euryteles that are often not reliably identifiable (Marques 1995; Schuchert 2008b); for this reason Schuchert (2008b) listed this species as Eudendrium cf. merulum, a species complex. It is a non-indigenous species, probably introduced in the Mediterranean Sea by shipping (Gravili et al. 2010; Occhipinti-Ambrogi et al. 2011). References. Bavestrello & Piraino (1991), Piraino et al. (1999), Marques et al. (2000a, b), Peña Cantero & García Carrascosa (2002), Bouillon et al. (2004), De Vito (2006), Gravili (2006), Gravili et al. (2008a), Schuchert (2008b), Morri et al. (2009), Puce et al. (2009), Gravili et al. (2010), Occhipinti-Ambrogi et al. (2011).

Published as part of 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, pp. 1-187 in Zootaxa 3908 (1) on pages 29-30, DOI: 10.11646/zootaxa.3908.1.1, http://zenodo.org/record/242729