Stylactaria inermis ( Allman, 1872 )

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 : 20-21

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 .

Figures

FIGURE 11. Stylactaria inermis: A, gastrozooid; B, dactylozooid (A, B same scale bar); C, nematocysts (drawn by C. G. Di Camillo). Scale bars: A, B, 0.5 mm; C, 10 µm.