Obelia geniculata (Linnaeus, 1758)

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 : 154-155

Obelia geniculata (Linnaeus, 1758)

Fig. 109 A–C

See Peña Cantero & García Carrascosa (2002) for a complete synonymy.

Material examined. HCUS-S 116 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp stage.

Description (based on our own observations; Schuchert 2001a; Peña Cantero & García Carrascosa 2002):

Hydroid. Hydrorhiza reptant, composed of numerous ramified thick stolons; colonies erect; hydrocauli usually unbranched, monosiphonic, up to about 20 mm, markedly flexuose, internodes curved, thickened (more evident in older parts), usually one side thicker than the other and alternate towards the internodes, which are ringed basally, hydrothecal pedicels short (composed of 2–3 wide annuli), alternate, borne laterally at distal end of each internode; hydrotheca bell-shaped, not very deep, walls and diaphragm thickened, rim smooth. Gonothecae on stem or on stolon, on short annulated pedicels, inverted-conical to cylindrical, narrower at their base, distal end wider than base, with a central tubular aperture.

Cnidome. Atrichous haplonemes and basitrichous, microbasic mastigophores.

Habitat type. Littoral species, in the Mediterranean occurring from the tidal level to 35 m depth ( Boero & Fresi 1986; Vervoort 1993); in brackish water, down to 1‰ salinity ( Cornelius 1995).

Substrate. Algae, phanerogams, ascidians, hydrozoans, bryozoans, molluscs, cirripedes, Isopoda, Hippocampus guttatus , sponge.

Seasonality. Throughout the year ( Boero & Fresi 1986) in the Ligurian Sea; February, April, June (De Vito 2006; this study), and November ( Piraino et al. 2013) in Salento waters.

Reproductive period. In the Mediterranean Sea, fertile colonies occur in January ( Boero & Fresi 1986; Vervoort 1993), February (Gili 1986), March ( Boero & Fresi 1986; Gili 1986; Roca 1986), April ( Roca 1986; De Vito 2006; this study), May ( Stechow 1919; Morri 1981b; Boero & Fresi 1986; Roca 1986), June ( Morri 1981b; Roca 1986), July ( Picard 1958b; Morri 1981b; Boero & Fresi 1986), August ( Picard 1958b; Morri 1981b), September ( Morri 1981b), October ( Billard 1936; Boero & Fresi 1986), and November ( Boero & Fresi 1986; Gili 1986).

Medusa. Not distinguishable from other species of Obelia (see O. dichotoma above).

Distribution. Cosmopolitan ( Medel & López-González 1996; Medel & Vervoort 2000; Schuchert 2001a; Peña Cantero & García Carrascosa 2002; Bouillon et al. 2004; Gravili et al. 2008a).

Records in Salento. Rare at: Torre Vado ( Presicce 1991); Otranto (De Vito 2006; Gravili 2006; Gravili et al. 2008a; Piraino et al. 2013; this study); Costa Merlata ( Andreano 2007); La Strea (C. Gravili unpublished observations).

Remarks. O. geniculata has been often reported as very common and abundant (e.g. Boero & Fresi 1986) but, in Salento, is currently rare. Puce et al. (2009) repeated the observations by Boero & Fresi (1986) at the same place where the species was formerly dominant, but did not record it. Medusae not seen in the present study.

References. Schneider (1898) as Campanularia coruscans, Lo Bianco (1909) , Stechow (1919, 1923), Billard (1923, 1936), Leloup (1934) as Laomedea geniculata, Zirpolo (1939) , Rossi (1950) as L. geniculata, 1971 ; Picard (1952, 1955, 1958a), Riedl (1959, 1966, 1970), Rossi (1961, 1971), Riedl (1966, 1991), Rossi (1971), Schmidt (1973) as L. geniculata, Chimenz Gusso & Rivosecchi Taramelli (1975) , Riggio & Mazzola (1976), Repetto et al. (1977), García Corrales et al. (1978), Morri (1979c, 1980, 1981a,b, 1985), Boero (1981a, 1985), García Carrascosa (1981), Morri & Martini (1981), Morri & Bianchi (1983), Boero et al. (1985), Isasi (1985), Boero & Fresi (1986), Gili (1982, 1986), Maluquer (1985), Roca (1986, 1987), García-Rubies (1987), Llobet i Nidal (1987), Llobet et al. (1986, 1991), Ramil (1988), Vervoort (1993), Altuna (1994), El-Beshbeeshy (1995), Caltagirone et al. (1996), Medel & López-González (1996), Piraino et al. (1999), Medel & Vervoort (2000), Schuchert (2001a), Peña Cantero & García Carrascosa (2002), Bedini et al. (2003), Bouillon et al. (2004), De Vito (2006), Gravili (2006), Galea (2007), Gravili et al. (2008a), Brahim et al. (2010), Piraino et al. (2013).

Figures

FIGURE 109. Obelia geniculata: A, part of colony with erect unbranched stems; B, detail of a part of stem; C, gonotheca (A, C redrawn and modified after Cornelius 1995 by A. Gennari; B drawn by C. G. Di Camillo). Scale bars: B, C, 0.5 mm.