Zanclea costata Gegenbaur, 1856

Fig. 47 A–E

See Schuchert (2010) for a complete synonymy.

Material examined. HCUS-S 0 52 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp stage.

Description (based on our own observations; Brinckmann-Voss 1970 as Zanclea implexa var. neapolitana; Gravili et al. 1996; Cerrano et al. 1997; Boero et al. 2000; Schuchert 2010):

Hydroid. Hydrorhiza as a creeping, branched stolon system; colony stolonal; hydrocaulus as hydranth pedicel, covered by perisarc, corrugated to annulated; hydranths cylindrical; with 4–6 capitate tentacles in an oral whorl; about 40–60 capitate aboral tentacles scattered over entire hydranth body; medusa buds scattered, each arising on a stalk between tentacles in the mid-upper part of hydranth, up to 20 may be present, advanced buds with two pairs of unequally developed marginal bulbs. Colour: perisarc brownish.

Habitat type. The hydroids can be found in rather shallow coastal waters (2.5– 5 m of depth) (Boero & Fresi 1986; Cerrano et al. 1997).

Substrate. The polyps grow on shells of Bivalvia, imbedded in the sediment, mostly on Chamelea gallina (L.), but also on Spisula subtruncata (da Costa), Venus ovata Pennant, and Cardium spp.

Seasonality. From January to December in the Ligurian Sea (Boero & Fresi 1986); July (Gravili et al. 1996); February–June (this study).

Reproductive period. In the Ligurian Sea, fertile colonies occur from May to August (Boero & Fresi 1986; Cerrano et al. 1997); from March to June (Brinckmann-Voss 1987) in the Tyrrhenian Sea.

Medusa. Adult. Bell-shaped, mesoglea slightly thicker at apex; exumbrellar nematocysts in linear, meridional tracks running from the bulbs upwards, length variable and depending on age; gonads surround manubrium, females with more than 10 eggs; fully grown with 2–4 tentacles bearing numerous cnidophores, all attached in a linear series, stalks of cnidophores variable, short proximal, longest distal.

Developmental stages. Newly released medusa almost spherical; with 4 perradial, oval nematocyst buttons containing stenoteles on exumbrella; manubrium simple, tubular, spanning about half of the subumbrellar cavity; 4 radial canals, well visible, no linear swellings; no gonads visible; 4 marginal bulbs, one opposite pair large, the other very small; each large bulb bearing one long, tapering, contractile tentacle with about 50 cnidophores, cnidophores all on one side of tentacle, contractile, each with usually 3–5 macrobasic euryteles, distally with long cilia.

Cnidome. Stenoteles of two sizes in tentacle capitations; large holotrichous macrobasic euryteles with a shaft coiled spirally along the main axis of undischarged capsules, charged shaft about six-times as long as capsule, abundant in hydrorhiza and rare in hydranth body; microbasic mastigophores rare in hydranth and hydrorhiza (polyp); two size-classes of stenoteles, telotrichous macrobasic euryteles in cnidophores (medusa).

Distribution. Endemic to the Mediterranean (Gegenbaur 1856; Hargitt 1904; Brückner 1914; Prévot 1959; Brinckmann-Voss 1970; Gravili et al. 1996, 2008a; Medel & López-González 1996; Cerrano et al. 1997; Boero et al. 2000; Peña Cantero & García Carrascosa 2002), all other records have to be confirmed on basis of hydroid cnidome studies (see Schuchert 2010).

Records in Salento. Rare in the Palude del Capitano (Presicce 1991; Gravili et al. 1996).

Remarks. Only the hydroid stage was seen in the present study. The medusa can be parasitized by the nudibranch Phyllirhoe bucephala Péron and Lesueur; the parasitized form has been given its own name, Mnestra parasites, and loses its tentacles (Krohn 1853; Caziot 1921; Ankel 1952; Martin & Brinckmann-Voss 1963; Martin 1966).

References. Mayer (1910), Brückner (1914), Russell (1953), Trégouboff & Rose (1957), Kramp (1957, 1959, 1961), Picard (1958a), Brinckmann-Voss (1970) as Z. costata var. neapolitana; Goy (1985), Presicce (1991), Riedl (1991), Gravili et al. (1996, 2008a), Medel & López-González (1996), Cerrano et al. (1997), Buecher & Gibbons (1999), Piraino et al. (1999), Boero et al. (2000), Peña Cantero & García Carrascosa (2002), Bouillon et al. (2004), Milos & Malej (2005), Benović et al. (2005), Batistić et al. (2007), Puce et al. (2009).