Halecium pusillum (M. Sars, 1857)

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 : 94-95

Halecium pusillum (M. Sars, 1857)

Fig. 66 A–C

See Peña Cantero & García Carrascosa (2002) for a complete synonymy.

Material examined. HCUS-S 0 73 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula).

Description (based on our own observations; Peña Cantero & García Carrascosa 2002):

Hydroid. Hydrorhiza as creeping stolon system; colonies erect, delicate; hydrocauli monosiphonic, perisarc of internodes thin and annulated throughout, apical stolons frequent; hydrocladia originating laterally, below hydrothecae, curved at base; hydrothecae at end of each internode, shallow, walls straight at basal half and curved outward at distal half, with a ring of desmocytes above diaphragm, secondary hydrothecae present, arising directly from primaries. Gonothecae: female gonothecae ringed throughout, with a lateral aperture with 2 hydranths, male gonothecae oval, elongated and with transverse undulations.

Cnidome. Microbasic euryteles and mastigophores.

Habitat type. Littoral species, ranging from the tidal level down to 40 m depth ( Rossi 1961; García Carrascosa 1981; Boero & Fresi 1986).

Substrate. Epibiotic on a wide range of organisms, such as algae, Posidonia , Cymodocea nodosa , Zostera leaves, other hydroids, bryozoans, cirripedes, mussels, Anthozoa.

Seasonality. January–December ( Boero & Fresi 1986) in the Ligurian Sea; February–September and November (De Vito 2006; Piraino et al. 2013; this study) in Salento waters.

Reproductive period. February ( Stechow 1919; Coma et al. 1992); March (Gili 1986; Coma et al. 1992); April ( Boero & Fresi 1986; Coma et al. 1992); September ( Faucci & Boero 2000); October ( Boero & Fresi 1986); February–April (Llobet i Nidal 1987).

Distribution. Eastern and western Atlantic, Mediterranean, Indo-Pacific ( Billard 1926; Philbert 1935; Leloup 1937, 1960; Rossi 1961; Teissier 1965; Fey 1970; Boero 1981a, b; Isasi 1985; Boero & Fresi 1986; Ramil 1988; Park 1993; Altuna 1994; Medel & López-González 1996; Medel et al. 1998; Peña Cantero & García Carrascosa 2002; Bouillon et al. 2004; Gravili et al. 2008a; Morri et al. 2009; Puce et al. 2009; Soto Ãngel & Peña Cantero 2013).

Records in Salento. Moderately frequent at: S. Caterina, Torre Vado ( Presicce 1991); La Strea, Porto Cesareo ( Denitto 1996; Faucci & Boero 2000; Miglietta et al. 2000; Ventura 2011); Costa Merlata ( Fraschetti et al. 2002); Torre Lapillo ( Andreano 2007); Grotta del Ciolo (Denitto et al. 2007); Otranto ( Fraschetti et al. 2002; De Vito 2006; Gravili 2006; Gravili et al. 2008a; Ventura 2011; Piraino et al. 2013; this study). Other Apulian records: Gargano ( Fraschetti et al. 2002).

Remarks. Halecium pusillum also forms vegetative shoots (frustules) for asexual reproduction ( Huvé 1955) that have been observed also by Boero and Fresi (1986), Ramil (1988), and Coma et al. (1992). In Otranto, colonies have been found with symbiotic zooxanthellae (De Vito 2006; this study).

References. Motz-Kossowska (1911), Broch (1912, 1933), Babic (1913a), Stechow (1919) also as Halecium annulatum ; Leloup (1934), Picard & Le Roch (1949), Picard (1952, 1958a), Rossi (1961), Repetto et al. (1977), García Carrascosa (1981), Morri (1985), Morri & Bianchi (1985), Boero & Fresi (1986), Gili (1986), Llobet et al. (1986, 1991), García Rubies (1987), Llobet i Nidal (1987), Piraino & Morri (1990), Morri et al. (1991), Coma et al. (1992), Altuna (1994), Medel & López-González (1996), Medel et al. (1998), Morri & Bianchi (1999), Piraino et al. (1999), Faucci & Boero (2000), Miglietta et al. (2000), Fraschetti et al. (2002), Peña Cantero & García Carrascosa (2002), 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), Ventura (2011), Piraino et al. (2013).

Figures

FIGURE 66. Halecium pusillum: A, hydroid with planktonic propagules; B, hydroid with female gonotheca; C, hydroid with male gonotheca (A, B, C same scale bar) (drawn by F. Boero). Scale bar: 1.0 mm.