Perarella schneideri (Motz-Kossowska, 1905)

Fig. 9 A–B

See Schuchert (2007) for a complete synonymy.

Material examined. HCUS-S 0 0 9 and HCUS-S 0 10 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula).

Description (based on our own observations; Bavestrello et al. 2000; Schuchert 2007):

Hydroid. Hydrorhiza reticulated with tubes of transparent perisarc; colonies stolonal, associated with the bryozoan Schizoporella longirostris,. Polyps with a perisarc collar at base, of two types, one long and tubular, with 8–14 filiform tentacles in one whorl, the other very extensile, filiform with only 4 short oral tentacles. Gonophores arising directly from the stolon, giving rise to free medusoids, almost spherical, with four radial canals, circular canal, four tentacular bulbs and a non functional manubrium. Colours: hydranths red, male gonophores whitish with dark red gastrovascular canals.

Eumedusoid: female eumedusoids with 80 or more eggs, free swimming for about 5 days before spawning and afterwards degenerating, male eumedusoids do not swim.

Cnidome. Desmonemes and microbasic euryteles.

Habitat type. Colonies usually associated with colonies of the bryozoan Schizoporella longirostris, sometimes other substrates (1 until more 100 m depth) (Boero & Fresi, 1986; Schuchert, 2007).

Substrate. Alghe (Caulerpa, Cystoseira mediterranea, Halimeda tuna) hydrozoans (Sertularella fusiformis), bryozoans (Membranipora spp., Schizoporella longirostris), mollusks (Pinna nobilis).

Seasonality. Present all year (Boero & Fresi 1986; Bavestrello et al. 2000; Puce et al. 2009) in the Ligurian Sea; February, October–November in Salento waters (De Vito 2006; this study).

Reproductive period. In the Ligurian Sea (Bavestrello et al. 2000), reproductive colonies occur from May to June.

Distribution. Mediterranean endemic (Bouillon 2004; Gravili et al. 2008a).

Records in Salento. Moderately frequent in the following localities: S.ta Caterina (Presicce 1991); Otranto (De Vito 2006; Gravili 2006; Gravili et al. 2008; this study).

Remarks. The two kinds of gastrozooids of Perarella schneideri are related to two different trophic strategies (the large gastrozooids feed on meiobenthic organisms like nematodes and polychaetes or bryozoan larvae; the filiform gastrozooids engulf and feed on the distal portion of a single lophophoral tentacle of its bryozoan host). When the lophophore retracts the gastrozooid is dragged into the bryozoan for a short time, and sucks the tentacle feeding on the food caught by the bryozoan lophophore (Bavestrello et al. 2000), in the same fashion described for Halocoryne epizoica (see below) (Piraino et al. 1992). As described for Stylactaria inermis eumedusoids (Onofri et al. 2010), the eumedusoids of P. schneideri are able to transform back to the polyp stage (Piraino et al. 2004).

References. Motz-Kossowska (1905) as Perigonimus schneideri; Billard (1936), Picard (1958a), Bavestrello (1985), Boero & Fresi (1986), Gili (1986), Llobet et al. (1986, 1991), Balduzzi et al. (1995), Piraino et al. (1999), Bavestrello et al. (2000) (all as Perarella schneideri), Bouillon et al. (2004), De Vito (2006), Gravili (2006), Gravili et al. (2008a).