Halecium mediterraneum Weismann, 1883

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 : 90-91

Halecium mediterraneum Weismann, 1883

Fig. 63 A–C

See Schuchert (2005b) for a complete synonymy.

Material examined. HCUS-S 0 70 (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula). Description (based on our own observations; Schuchert 2005b):

Hydroid. Hydrorhiza tubular, creeping, ramified; colony erect, bushy, hydrocauli often distally geniculate, usually monosiphonic, sometimes polysiphonic, 1–3 cm high, with regular succession of alternately inclined internodes, with distinct nodes, each with a distal oblique hydrophore, alternately pointing left or right, surpassing the level of distal node, perisarc of internodes smooth, near nodes somewhat bulging; hydrocladia originate from primary hydrophores or from below them, branching dichotomously or trichotomously; hydranth with 18–20 tentacles; primary hydrotheca gradually widening and rim somewhat everted or rolled, desmocytes present, sometimes below diaphragm a semicircular thickening on adcauline side (pseudodiaphragm), hydrothecae often renewed. Gonothecae arising in upper axils of branching points and hydrophores; dimorphic, colonies gonochoric, gonothecae of both sexes without protruding hydranths, female ones smooth, ovoid to rectangular, always compressed, along sides a crease-line, distal end obtuse, with or without curved notchlike opening of variable breadth and depth, mature female gonothecae with thin perisarc capsule inside, enveloping the oblong gonangium, with surface epidermis with numerous nematocysts, 6– 13 eggs, about 0.1 mm in diameter, development to planula within gonotheca (larviparity); male gonothecae smaller, ovoid, length up to 0.7 mm, compressed, sides with crease, distal end rounded, without notch or inner secondary capsule, opening slit-like, with one oblong sperm mass. Colours: colonies yellow-brown.

Cnidome. Microbasic mastigophores.

Habitat type. Colonies growing on rock and other substrates, occasionally mass occurrence covering areas of square meters forming a lawn or tangled mass of stems; coralligenous bottom; Posidonia (depth range: 0.5– 145 m) ( Boero & Fresi, 1986; Peña Cantero & García Carrascosa 2002).

Substrate. Algae, Posidonia oceanica , Spirographis tubes, hydrozoans, bryozoans, sponges, cirripeds, anthozoans.

Seasonality. March–November ( Motz-Kossowska 1911 as H. gracile ; Peña Cantero & García Carrascosa 2002; Schuchert 2005b; Galea 2007) in the western Mediterranean; February, March, May, August, September (this study).

Reproductive period. April–November ( Motz-Kossowska 1911; Peña Cantero & García Carrascosa 2002; Schuchert 2005b; Galea 2007); April ( Stechow 1919).

Distribution. Mediterranean, perhaps also adjacent Atlantic Ocean from Morocco to Galicia (Medel & López- González 1996; Bouillon et al. 2004; Schuchert 2005b; Gravili et al. 2008a).

Records in Salento. Rare at: Torre dell’Inserraglio, S.ta Caterina, Montagna Spaccata, La Rotonda, Torre Vado, Ponte del Ciolo ( Presicce 1991); Otranto (Gravili 2006; Gravili et al. 2008a); La Strea (Porto Cesareo) ( Ventura 2011 as Halecium delicatulum ).

Remarks. Medel and López-González (1996) consider H. mediterraneum as conspecific with H. delicatulum ; Bouillon et al. (2004) considered H. mediterraneum as a doubtful species. Schuchert (2005b) kept the nominal species H. mediterraneum and H. delicatulum separate because of slight differences, and mainly for biogeographic reasons, although he acknowledged that they are very similar.

References. Stechow (1919, 1923), Riedl (1959), Repetto et al. (1977); García Corrales et al. (1978) as Halecium tenellum ; Medel & López-González (1996), Piraino et al. (1999), Peña Cantero & García Carrascosa (2002) as Halecium delicatulum ; Bouillon et al. (2004), Schuchert (2005b); Gravili (2006) as H. delicatulum ; Galea (2007); Gravili et al. (2008a) as H. delicatulum ; Puce et al. (2009), Bianchi et al. (2011), Ventura (2011).

Figures

FIGURE 63. Halecium mediterraneum: A, branching pattern of stem; B, female gonotheca; C, male gonotheca (B and C same scale bar) (drawn by C. G. Di Camillo). Scale bars: A, B, 0.5 mm.