Amphinema rugosum (Mayer, 1900)

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 : 45-46

Amphinema rugosum (Mayer, 1900)

Fig. 30 A–C

See Schuchert (2007) for a complete synonymy.

Material examined. HCUS-S 0 35 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp stage.

Description (based on our own observations; Rees & Russell 1937; Russell 1953; Schuchert 2007, 2012):

Hydroid. Hydrorhiza as creeping stolons; colonies stolonal; hydrocauli unbranched or slightly branched, perisarc extending to the middle of the hydranth body where it adheres to polyp with a well marked end, often covered by detritus, with 2–5 annulations at hydrocauli base; hydranths fusiform; hypostome dome-shaped; 8–12 amphicoronate filiform oral tentacles in one whorl; medusa buds covered by thin perisarc, borne on pedicels shorter than bud height, arising from stolons and hydrocauli, 1–3 buds per hydrocaulus. Colours: perisarc horn coloured, hydranths and coenosarc bright reddish orange.

Habitat type. Rocky cliffs and concretions, depth range: 0.5– 20 m ( Boero & Fresi 1986; Puce et al. 2009; own data).

Substrate. The polyp stage occurs on a variety of hard substrata (algae, sponge, bryozoa, mussels, polychaetes tubes).

Seasonality. In the Mediterranean Sea from January to December ( Boero & Fresi 1986; De Vito 2006; Puce et al. 2009; this study).

Reproductive period. In the Ligurian Sea, fertile colonies occur from July to September, November ( Boero & Fresi 1986), and in April (Puce et al. 2009); from August to November (De Vito 2006; this study) in Salento waters.

Medusa. Adult. Umbrella bell-shaped, up to 6 mm high, slightly higher than wide, mesoglea uniformly thin besides top, with a large conical to hemispherical apical projection and slight perradial furrows in top umbrella; manubrium flask-shaped, cruciform in section, reaching almost umbrella margin; mouth cruciform, with 4 prominent, slightly recurved lips; 4 broad radial canals with jagged and smooth margins; 8 gonads in adradial pairs, with 3–4 characteristic folds directed interradially; 2 diametrically opposed, large, hollow, conical, tapering and very long bulbs; each bulb with one very long tentacle, up to ten times bell size, with 14–24 small marginal tentaculae; without ocelli. Colours: marginal tentacle bulbs and stomach rich brownish yellow to orange, with central masses of deep purple-brown pigment; cores of two marginal tentacles ochre; marginal tentaculae colourless.

Developmental stages. Newly released medusa spherical, with small apical projection, exumbrella with scattered nematocysts; manubrium half the length of the subumbrellar cavity; with 2 opposite marginal tentacular bulbs, each bearing one tentacle, with or without 2 small opposite perradial tiny tentacles (tentaculae). Colours: tentacle bulbs reddish-orange, with slight tinge of yellow, stomach bright ochreish yellow.

Habitat type. The medusa of this species lives generally in the deeper water layers below 20 m, but may migrate right to the surface at night (Schuchert 2007).

Cnidome. Desmonemes and microbasic euryteles (hydroid); microbasic euryteles (medusa).

Distribution. Atlantic, Indo-Pacific, Mediterranean ( Mayer 1910; Uchida 1927; Russell 1953; Kramp 1959, 1961, 1965; Allwein 1968; Bouillon 1980; Wedler & Larson 1986; Goy et al. 1990, 1991; Cornelius 1992; Medel & López-González 1996; Migotto 1996; Schuchert 1996, 2007; Gravili et al. 2008a; Morri et al. 2009; Puce et al. 2009).

Records in Salento. Rare at: Grotta del Ciolo (Denitto et al. 2007); Otranto (De Vito 2006; Gravili 2006; Gravili et al. 2008a; Piraino et al. 2013; this study).

Remarks. Prior to life cycle investigation, Amphinema rugosum was frequently confused with A. dinema (see Rees & Russell, 1937). While it is not possible to distinguish the hydroids of the two species in the absence of medusa buds (see Schuchert 2007), or genetic data, the medusae and hydroids with medusa buds are readily differentiated. Only the hydroid stage and the new born medusa were seen in the present study.

References. Rees & Russell (1937), Russell (1953), Roper et al. (1983), Boero & Fresi (1986), Brinckmann- Voss (1987), Bouillon (1995), Schuchert (1996, 2007, 2012), Migotto (1996), Bouillon et al. (2004), De Vito (2006), Gravili (2006), Denitto et al. (2007), Gravili et al. (2008a), Morri et al. (2009), Puce et al. (2009), Piraino et al. (2013).

Figures

FIGURE 30. Amphinema rugosum: A, fragment of a hydroid colony with medusa buds; B, nematocysts; C, adult medusa (A – B drawn by F. Boero; C redrawn and modified after Russell 1953 by C. G. Di Camillo). Scale bars: A, C, 1.0 mm; B, 10 µm.