Halecium petrosum Stechow, 1919

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 : 93-94

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).

Figures

FIGURE 65. Halecium petrosum: A, fragments of hydrocladia with hydrothecae; B, detail of hydrothecal rim; C, fragments of hydrocladia with hydrothecae and female gonotheca, D, with male gonotheca (C, D same scale bar) (A, B drawn by C. G. Di Camillo; C, D redrawn and modified after Motz-Kossowska 1911). Scale bars: A, 0.5 mm; C, D, 0.5 mm.