Porpita porpita (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 : 64-66

Porpita porpita (Linnaeus, 1758)

Fig. 44 A–C

See Schuchert (1996) for a complete synonymy.

Material examined. HCUS-S 0 49 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—medusa stage.

Description (based on our own observations; Vanhoeffen 1906; Brinckmann-Voss 1970; Bouillon 1984a; Calder 1988; Pagès et al. 1992; Schuchert 1996):

Hydroid. Floating polymorphic colony, up to 30 mm diameter but mostly smaller, with disk-shaped mantle and internal float: margin soft and flexible, central region firm, slightly convex and with a central pore and numerous stigmata, mantle with radiating endoderm canals, internal chitinous float consisting of a series of concentric chambers, with a disk-shaped reservoir of cnidocysts between float and central gastrozooid, under surface with one large central gastrozooid, a median circle of gastro-gonozooids, and a peripheral circle of dactylozooids; gastrozooid central, short and broad, with a terminal mouth, without tentacles or prominent cnidocyst clusters; dactylozooids with a distal whorl of 4 capitate tentacles and a varying number of short, small capitate tentacles in 3 vertical rows on hydranth body; gastro-gonozooids clavate, lacking tentacles but with prominent cnidocyst clusters scattered over body, medusae buds developing near base in clusters. Colours: colony dark blue coloured.

Habitat type. Colony floating on water surface ( Vanhöffen 1906; Calder 1988).

Seasonality. In the Mediterranean Sea, Porpita porpita occurs in May, June, September–October ( Lo Bianco 1909; Tregouboff & Rose 1957); July–August (F. Boero unpublished observations).

Reproductive period. Colonies usually bear small medusa buds throughout the period of presence on the water surface.

Medusa. Adult. Umbrella rather conical, up to 2 mm diameter and 2.5 mm high; exumbrella with 8 perradial tracks of nematocysts, only one capsule wide; manubrium conical with octagonal base, length one-third of subumbrellar cavity; mouth circular; 8 radial canals with zooxanthellae, circular canal present; gonads normally in 4 perradial masses on manubrium, but 3–8 gonads may be present; 8 little-developed marginal bulbs, short exumbrellar cnidocyst tracks above each bulb; 2 opposite marginal capitate tentacles; without ocelli.

Developmental stages. Newly released medusae with bell-shaped umbrella, slightly higher (height 0.3 mm) than wide; 4 exumbrellar rows of nematocysts; manubrium very short; 4 broad radial canals, with zooxanthellae on gastrodermis; circular canal missing; tentacles lacking.

Cnidome. Atrichous isorhizas, haplonemes, and three types of stenoteles (polyp); stenoteles and telotrichous macrobasic euryteles (medusa).

Distribution. Atlantic, Indo-Pacific, Mediterranean ( Moser 1925; Totton 1954; Brinckmann-Voss 1970; Daniel 1976; Bouillon 1984a; Pagès et al. 1992; Schuchert 1996; Bouillon et al. 2004; Gravili et al. 2008a).

Records in Salento. Common and moderately frequent along the Ionian and Adriatic Apulian coasts: Tricase Porto, Torre dell’Orso, Roca, San Foca, (Gravili 2006; Gravili et al. 2008a; F. Boero unpublished observations).

Remarks. Gonothecae and medusae not seen in the present study. The adult medusae of Porpita porpita are not known from the Mediterranean; they have been described only from Papua New Guinea ( Bouillon 1984a).

References. Brinckmann-Voss (1970, 1987), Bouillon (1984a), Pagès et al. (1992), Medel & López-González (1996), Gravili (2006), Gravili et al. (2008a).

Figures

FIGURE 44. Porpita porpita: A, colony (seen from above); B, mature colony (lateral view); C, medusa (A and B same scale bar) (A, C redrawn and modified after Schuchert 1996, B after Pagès et al. 1992 by A. Gennari). Scale bars: A, B, 10 mm; C, 2.0 mm.