Gastroblasta raffaelei Lang, 1886

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 : 151-152

Gastroblasta raffaelei Lang, 1886

Fig. 107 A–H

See Gravili et al. (2007) for a complete synonymy.

Material examined. HCUS-S 114p and HCUS-S 114m (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp and medusa stages.

Description (based on our own observations; Gravili et al. 2007):

Hydroid. Hydrorhiza stolonal, embedded in the body of sponges; colonies stolonal; hydrocauli partially embedded in the sponge tissues, arising from both the oscula and the surface of the host; hydranth with peduncled hypostome; with about 16 amphicoronate tentacles; hydrotheca about 0.25 mm high, slightly broader than high, usually with 8 broader than high cusps with doubled rim, diaphragm present, with 3–4 annulations below subhydrothecal chamber. Gonothecae smooth, about 0.70 mm high, wide at distal end and tapering gradually below, borne on hydrorhiza, each containing a single medusa bud.

Habitat type and substrate. Living embedded in sponges of the genera Petrosia and Ircinia (depth: 0.5– 6 m) ( Boero & Fresi 1986; Gravili et al. 2007).

Medusa. Adult. Umbrella more or less elliptical, up to 6 mm wide; up to 9 complete and 7 rudimentary urnshaped manubria; mouth of every manubrium with 4 simple lips each; with up to 20 radial and centripetal canals; gonads sometimes developed in the middle parts of one or more radial canals; with 26 well developed marginal tentacles and 17 rudimentary ones; 34 marginal statocysts.

Developmental stages. Newly released medusa with umbrella hemispherical, almost 1 mm wide and 0.6 mm high; mouth with 4 lips; 4 radial canals; no gonads on radial canals; velum broad, with a narrow opening; 4 pearshaped tentacular bulbs; each marginal bulb bearing a tentacle; 8 statocysts, each with one (sometimes two) statolith, in couples between adjacent tentacles.

Cnidome. Microbasic mastigophores.

Seasonality. February ( Boero 1980b), and July–October ( Boero & Fresi 1986) in the Ligurian Sea; March–October (De Vito 2006; this study), November ( Piraino et al. 2013), and May (Gravili et al. 2007) in Salento waters.

Reproductive period. February ( Boero 1980b) in the Ligurian Sea; April (De Vito 2006; this study), and May (Gravili et al. 2007) in Salento waters.

Distribution. Mediterranean (Bouillon et al. 2004; Gravili et al. 2007, 2008a).

Records in Salento. Moderately frequent at Otranto (De Vito 2006; Gravili 2006; Gravili et al. 2007, 2008a; Piraino et al. 2013; this study).

Remarks. The whole life cycle was examined in the present study. Gastroblasta raffaelei is the only leptomedusan hydroid exclusively living in symbiosis with sponges ( Puce et al. 2005b). The medusa can reproduce by fission (see Russell 1953; Cornelius 1982; Gravili et al. 2007).

References. Lang (1886), Mayer (1910), Neppi & Stiasny (1913) as Phialidium variabile ; Vannucci (1966), Boero (1980b), Boero & Fresi (1986), De Vito (2002, 2006), Bouillon et al. (2004), Puce et al. (2005b), Gravili et al. (2007, 2008a), Piraino et al. (2013).

Figures

FIGURE 107. Gastroblasta raffaelei: A, hydranth with 2 gonothecae inside the sponge Ircinia sp.; B, hydranth; C, gonotheca; D, newly liberated medusa; E, 4 - day-old-medusa; F, 10 - day-old-medusa (E and F same scale bar); G, medusa during fission process; H, adult medusa (28 - day-old) (modified after Gravili et al. 2007). Scale bars: A, C, D, E, F, H, 1.0 mm; B, 0.5 mm; G, 2.0 mm.