Hydranthea margarica Hincks 1862

Hydranthea margarica (Hincks, 1862)

Fig. 83 A–F

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

Material examined. HCUS-S 0 91 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp stage.

Description (based on our own observations; Boero & Sarà, 1987; Cornelius 1995; Peña Cantero & García Carrascosa 2002):

Hydroid. Colonies stolonal bearing single hydranths at irregular intervals; hydrorhiza as stolon system with haustorial projections beneath providing additional attachment; hydranth very elongated, slender, not retractable in hydrothecae, widest just below bases of tentacles and tapering gradually to base, endodermal epithelium differentiated into distinct part the upper digestive, the basal part formed by chordal cells; hypostome conical; 20–30 amphicoronate tentacles with intertentacular web; hydrothecae very short, collar-shaped with slightly divergent walls and basal diaphragm, on smooth short pedicels inserted directly to stolon. Gonothecae short or absent, when present a shallow dish on a short pedicel, each with a single eumedusoid, developing eggs reported in hydrorhiza of colonies lacking gonophores. Colour: hydranth yellowish-white.

Habitat type. Littoral (depth range: 10–20 m) (Boero & Fresi 1986; Peña Cantero & García Carrascosa 2002).

Substrate. Usually recorded epizoic on Bryozoa, hydroids, algae, and non-living substrata.

Seasonality. January–July, September–December (Llobet i Nadal 1987; Llobet et al. 1991), February–March (Puce et al. 2009), and August (Boero & Fresi 1986) in the western Mediterranean; through the year (De Vito 2006; this study) in Salento waters.

Reproductive period. February, April, May (De Vito 2006; this study) in Salento waters.; April–May (Llobet et al. 1991), August (Boero & Fresi 1986), and October (Motz-Kossowska 1911) in the western Mediterranean.

Eumedusoid: liberable eumedusoids, almost spherical, about 0.5 mm in diameter, with numerous cnidocysts on exumbrella; with 4 branched radial canals; gonads on manubrium filling the whole subumbrella; with 8 statocysts. Colours: radial canals filled with purplish or orange granules as well as ring canal; gonads orangepurple.

Cnidome. Merotrichous haplonemes.

Distribution. Atlantic, Indo-Pacific (Seychelles), Mediterranean (Motz-Kossowska 1911; Picard 1951a; Huvé 1954; Millard & Bouillon 1973; García Carrascosa 1981; Boero & Fresi 1986; Gili 1986; Cornelius et al. 1990; Altuna 1994; Medel & López-González 1996; Peña Cantero & García Carrascosa 2002; Bouillon et al. 2004; Gravili et al. 2008a).

Records in Salento. Moderately frequent at: Porto Badisco (Presicce 1991); Il Chiapparo, Otranto (De Vito 2006; Gravili 2006; Gravili et al. 2008a; this study).

Remarks. The whole life cycle was examined in the present study. The presence of only eight statocysts in the eumedusoid could indicate some relationship of this genus with the genus Eucheilota, even though the position of the gonads on the manubrium suggest that the liberated stage is a swimming gonophore sensu Boero and Bouillon (1989).

References. Hincks (1868), Motz-Kossowska (1911) as Halecium margaricum, Halecium Billardii and Halecium Billardii var. exigum; Huvé (1954), Picard (1958a), Teissier (1965), García Carrascosa (1981), Boero & Fresi (1986), Gili (1986), Llobet et al. (1986, 1991), Llobet i Nadal (1987), Boero & Sarà (1987), Cornelius et al. (1990), Altuna (1994), Medel & López-González (1996), Piraino et al. (1999), Peña Cantero & García Carrascosa (2002), Bouillon et al. (2004), De Vito (2006), Gravili (2006), Gravili et al. (2008a), Puce et al. (2009).