Clytia viridicans Leuckart 1856

Clytia viridicans (Leuckart, 1856)

Fig. 106 A–C

See Pagliara et al. (2000) for a complete synonymy.

Material examined. HCUS-S 113 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp stage.

Description (based on our own observations; Pagliara et al. 2000):

Hydroid. Hydrorhiza stolonal, as thin, slightly ramified tubes; colonies stolonal; pedicel short, annulated at base and below hydrotheca; hydranths with peduncled hypostome; 14–18 amphicoronate tentacles, hydrotheca conical, with 7–9 cusps, projecting inwards and with outwards perisarc projections in bays between nearby cusps. Gonothecae on hydrorhiza, either corrugated or smooth, containing up to 4 developing green medusae buds.

Habitat type. Rocky shore (Pagliara et al. 2000).

Substrate. Algae, other hydroids, bryozoans, and barnacles.

Seasonality. From January to December in Salento waters (De Vito 2006; this study).

Reproductive period. April–July, and December (De Vito 2006; this study) in Salento waters.

Medusa. Adult. Umbrella flattened, about 11 mm wide, mesoglea thin; manubrium bottle-shaped on a short peduncle; mouth with 4 corrugated lips; gonads oval, elongated along the distal part of radial canals not reaching umbrellar margin; 16–32 marginal tentacles; 24–40 statocysts. Colours: exumbrella transparent, manubrium, gonads and tentacular bulbs bright green in living material.

Developmental stages. Newly released medusa with umbrella hemispherical, about 0.5 mm high, a row of nematocysts often present on exumbrella, parallel to umbrellar margin; manubrium tubular, reaching half of subumbrellar cavity; mouth with 4 lips; 4 radial canals; velum wide, with a small opening; 4 perradial tentacled bulbs, 4 small interradial bulbs sometimes present; 8 statocysts along the circular canal, with one statolyth each. Colour: umbrella bright green.

Two days after release, gonad rudiments developed on radial canals, along with other 4 tentacles on interradial marginal bulbs and other statocysts between adjacent tentacles; the umbrella tends to flatten; marginal bulbs, tentacles and statocysts are gradually added and, 30–45 days after release, medusae reach maturity.

Cnidome. Atrichous isorhizas and microbasic mastigophores.

Distribution. Endemic to Mediterranean Sea (Pagliara et al. 2000; Bouillon et al. 2004; Gravili et al. 2008a).

Records in Salento. Moderately frequent at: La Strea, Porto Cesareo (Faucci & Boero 2000); Otranto (Fraschetti et al. 2002; De Vito 2006; Gravili 2006; Gravili et al. 2008a; Piraino et al. 2013; this study); Torre dell’Inserraglio, Costa Merlata (Andreano 2007); Grotta del Ciolo (Denitto et al. 2007; Moscatello & Belmonte 2007); Il Chiapparo (C. Gravili unpublished observations).

Remarks. The whole life cycle was examined in the present study. Some planulae settled on the underside of the surface film of water and gave rise to floating colonies that developed for weeks in that position (for more details see Pagliara et al. 2000). As in all other Clytia species with amphicoronate tentacles, the tentacles oriented downwards lay on the perisarc projections between adjacent cusps, the ones oriented upwards are sustained by cusps. The number of tentacles, as a rule, should be double the number of cusps. Green forms attributed to Clytia hemisphaerica might be referable to the present species.

References. Haeckel (1864), Metschnikoff (1886a, b), Russell (1953), Cornelius (1982), Faucci & Boero (2000), Pagliara et al. (2000), Fraschetti et al. (2002), Bouillon et al. (2004), Denitto et al. (2007), Moscatello & Belmonte (2007), Gravili et al. (2008a), Piraino et al. (2013).