Halecium tenellum Hincks, 1861

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 : 96-97

Halecium tenellum Hincks, 1861

Fig. 67 A–C

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

Material examined. HCUS-S 0 74 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula).

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

Hydroid. Hydrorhiza stolonal, colonies erect; hydrocauli very thin and delicate, monosiphonic, up to 20 mm high, irregularly branched, internodes long, in a zigzag arrangement, separated by transverse nodes; hydrocladia may originate from hydrothecal base; hydrothecae shallow, walls widening from base to top giving a wide aperture, rim everted and curved outwards, borne laterally at upper part of internodes, alternate and provided with a well developed hydrophore, secondary hydrothecae provided with hydrophore, may arise from primary hydrothecae. Gonothecae: male gonothecae ovate and flattened, female similar but slightly larger and broader.

Cnidome. Microbasic euryteles and mastigophores.

Habitat type. Eurybathic species that has been found from 0.5 to 200 m depth ( Marinopoulos 1979; Boero & Fresi 1986).

Substrate. Algae, hydroids, concretions, Posidonia , bryozoans, polychaete tubes, anthozoans, sponge.

Seasonality. April ( Picard 1955; Gili 1986), May (Medel et al. 1998), and October–March, July ( Boero & Fresi 1986) in the western Mediterranean; June, July (De Vito 2006; this study) in Salento waters.

Reproductive period. April ( Picard 1955; Gili 1986) and May (Medel et al. 1998) in the western Mediterranean.

Distribution. Cosmopolitan species present in the eastern and western Atlantic, Mediterranean, Indo-Pacific, Arctic, Antarctic ( Broch 1918 in part as Halecium textum ; Stepan’yants 1979; Ramil & Vervoort 1992; Medel & López-González 1996; Medel et al. 1998; Peña Cantero & García Carrascosa 2002; Bouillon et al. 2004; Gravili et al. 2008a; Soto Ãngel & Peña Cantero 2013).

Records in Salento. Rare at Otranto (De Vito 2006; Gravili 2006; Gravili et al. 2008a; this study).

Remarks. It is not always easy to distinguish the European Halecium species H. mediterraneum , H. labrosum , and H. tenellum (for details see Schuchert 2005b). The distinctive characteristics of H. tenellum are that the colonies are more gracile , non-polysiphonic and smaller than those of the other two species, with internodes more elongate, strongly arranged in a zigzag manner.

References. Motz-Kossowska (1911), Broch (1912, 1933), Stechow (1919), Leloup (1934), Picard (1958a), Rossi (1961), Patriti (1970), Boero (1981a, b), Fresi et al. (1982), Boero & Fresi (1986), Gili (1986), Llobet et al. (1986, 1991), Llobet i Nadal (1987), Ramil & Vervoort (1992), Medel & López-González (1996), Migotto (1996), Medel et al. (1998), Piraino et al. (1999), Medel & Vervoort (2000), Peña Cantero & García Carrascosa (2002), Bouillon et al. (2004), De Vito (2006), Gravili (2006), Gravili et al. (2008a), Puce et al. (2009).

Figures

FIGURE 67. Halecium tenellum: A, part of stem; B, female gonophore; C, male gonophore (B, C same scale bar) (A drawn by C. G. Di Camillo; B, C redrawn and modified after Millard 1975 by C. G. Di Camillo). Scale bars: A, 0.1 mm; B, C, 0.5 mm.