Stylactaria inermis (Allman, 1872)

Fig. 11 A–C

See Schuchert (2008a, 2013) for a complete synonymy.

Material examined. HCUS-S 0 13 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula).

Description (based on our own observations; Stechow 1919, Boero 1981a both as Stylactis inermis; Schuchert 2008a as Hydractinia inermis):

Hydroid. Hydrorhiza without spines, as a network of stolons, colonies stolonal, only slightly polymorphic as gastrozooids and gonozooids are rather similar and dactylozooids may be present or absent; gastrozooids up to 4.2 mm high, with a basal perisarc cup; hypostome conical; about 20 tentacles in two or several whorls; gonozooids up to 2 mm, with two whorls of about 6–16 tentacles; colonies unisexual. Gonophores fixed, or liberable eumedusoids. Colours: hydranths pale pink to brownish.

Eumedusoid: radial canals and a narrow ring canal; no tentacle bulbs; no tentacle rudiments; no velum; females with 10– 20 eggs.

Cnidome. Microbasic euryteles of two size classes, desmonemes; Boero (1981a) also found very small anisorhiza-type nematocysts.

Habitat type. Posidonia, locally common on rocky coasts, occurs from a few meters to 40 m depth (Boero & Fresi, 1986; Schuchert 2008a).

Substrate. Algae, Posidonia oceanica, sponges, hydroids, barnacles, polychaete tubes, and other fixed substrates.

Seasonality. In the western Mediterranean Sea (Stechow 1919; García-Rubies 1987; Schuchert 2008a) in February, April–July; in the Ligurian Sea (Boero & Fresi 1986) from October to May; in Salento waters from September to May (De Vito 2006; Schuchert 2008a; this study).

Reproductive period. In the western Mediterranean Sea, reproductive colonies occur in April (Stechow 1919); April–May (Boero & Fresi 1986); July (García-Rubies 1987); February, April, May (Schuchert 2008a).

Distribution. Endemic to the Mediterranean (see Bouillon et al. 2004; Gravili et al. 2008a; Schuchert 2008a).

Records in Salento. Moderately frequent at: Torre dell’Inserraglio (Presicce 1991); Otranto (De Vito 2006; Gravili 2006; Gravili et al. 2008a; Ventura, 2011; this study).

Remarks. Bouillon et al. (1997) characterized the gonophores as eumedusoids with 8 tentacular bulbs. Schuchert (2008a) described the gonophores as sporosacs. Onofri et al. (2010) recorded reverse development of liberated eumedusoids of S. inermis, with transformation into stolons and polyps as described in Turritopsis dohrnii (Bavestrello et al. 1992; Piraino et al. 1996), Laodicea undulata (De Vito et al. 2006), and Perarella schneideri (Piraino et al. 2004) . Miglietta & Cunningham (2012) referred this nominal species to Stylactaria .

References. Stechow (1919 as Stylactis inermis, 1923 as Stylactella inermis), Leloup (1934) as Podocoryna inermis, Riedl (1959, 1966) as Stylactella inermis; Boero (1981a, b), Gili & Castelló (1985), Boero & Fresi (1986), Gili (1986), Roca et al. (1991), Piraino et al. (1999) all as Stylactis; Medel & López-González (1996) as Stylactaria; Bouillon et al. (1997), Peña Cantero & García Carrascosa (2002), Bouillon et al. (2004), De Vito (2006), Gravili (2006), Gravili et al. (2008a), Schuchert (2008a), Ventura (2011) all as Hydractinia inermis .