Halecium petrosum Stechow, 1919

Fig. 65 A–D

See Schuchert (2005b) for a complete synonymy.

Material examined. HCUS-S 0 72 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula). Description (based on our own observations; Schuchert 2005b):

Hydroid. Colonies erect; hydrocauli stiff, monosiphonic, up to 35 mm, with a thick perisarc; hydrocladia alternate, laterally at the end of each internode; hydrothecae sessile, but adcauline wall not adnate to the axis, walls gradually widening distally, rim not flared, hydrothecal renovations frequent, secondary hydrophore large and with undulated perisarc. Gonothecae: female gonothecae ovoid to spherical, big, aperture apical with 2 hydranths, borne on hydrorhiza or on hydrocauli, male gonothecae sac-shaped, elongated, arising from inside of the hydrotheca or below it.

Cnidome. Atrichous isorhizas.

Habitat type. Littoral and shelf species, but absent from the shallowest infralittoral (Peña Cantero & García Carrascosa 2002; Schuchert 2005b).

Substrate. Algae, other hydroids, Posidonia oceanica, anthozoans, incrusting sponge.

Seasonality. Always present in the western Mediterranean (Llobet i Nadal 1987; Llobet et al. 1991); April, August (De Vito 2006; this study) in Salento waters.

Reproductive period. August (Motz-Kossowska 1911; De Vito 2006; this study); September (Llobet et al. 1991; Coma et al. 1992); October (Stechow 1923; Llobet i Nadal 1987; Llobet et al. 1991; Coma et al. 1992); November (Llobet i Nadal 1987) in the Mediterranean Sea.

Distribution. Endemic to the Mediterranean (Medel & López-González 1996; Bouillon et al. 2004; Schuchert 2005b; Gravili et al. 2008a; Morri et al. 2009).

Records in Salento. Rare at: Otranto (De Vito 2006; Gravili 2006; Gravili et al. 2008a; this study); La Strea (Porto Cesareo) (Ventura 2011).

Remarks. Motz-Kossowska (1911) identified abundant material from Banyuls as Halecium robustum Pieper, 1884 . Female gonothecae of Motz-Kossowska’s material differed from typical H. lankesterii, and for this reason Stechow (1919) attributed it to a new species with the name Halecium petrosum .

References. Motz-Kossowska (1911) as H. robustum; Stechow (1919, 1923), Leloup (1934), Picard (1951a, 1958a), Rossi (1961), Llobet et al. (1986, 1991), Llobet i Nadal (1987), García-Carrascosa (1981), Llobet i Nidal (1987), Coma et al. (1992), Medel & López-González (1996), Peña Cantero & García Carrascosa (2002), Bouillon et al. (2004), Schuchert (2005b), De Vito (2006), Gravili et al. (2008a), Morri et al. (2009), Puce et al. (2009), Ventura (2011).