Clytia linearis (Thornely, 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 : 145-146

Clytia linearis (Thornely, 1900)

Fig. 103 A–G

See Calder (1991) for a complete synonymy.

Material examined. HCUS-S 110p and HCUS-S 110m (Hydrozoa Collection, University of Salento—fauna of the Salento Peninsula)—polyp and medusa stages.

Description (based on our own observations; Cornelius 1987; Altuna 1994; Lindner & Migotto 2002):

Hydroid. Hydrorhiza as a highly ramified stolonal system; colonies stolonal or erect, up to 40 mm high; pedicels (hydrocauli) unbranched or subsympodially branched, ringed basally and distally, topped by hydrothecae; branches (hydrocladia) arising laterally, at the upper part of the axis; hydrothecae very deep, cylindrical, sides almost parallel, narrowing basally, with a thin diaphragm, straight or slightly oblique, with wide margin, 10–12 acute cusps with characteristic longitudinal central perisarcal inwards ridges extended further of the cusps, giving a striated appearance to hydrotheca. Gonothecae elongate-oval, truncate distally, narrow sub-distally and basally, borne usually on axils, on short and ringed pedicels, enclosing up to 8 developing medusa buds.

Habitat type. Littoral and shelf species that has been found from the tidal level to 200 m depth ( Marinopoulos 1981; Boero & Fresi 1986) in the Mediterranean Sea.

Substrate. Algae, Posidonia oceanica , rock, hydroids, sponges, bryozoans, polychaete tubes, anthozoans, cirripedes, and mollusc shells.

Seasonality. July–August ( Peña Cantero & García Carrascosa 2002), throughout the year ( Boero & Fresi 1986; Llobet et al. 1991; De Vito 2006; Puce et al. 2009; this study) in several localities of the Mediterranean Sea.

Reproductive period. January ( Picard 1955), April ( Boero & Fresi 1986; Gili 1986), June ( Boero & Fresi 1986; Roca 1986), July ( Peña Cantero & García Carrascosa 2002), August ( Boero & Fresi 1986; Peña Cantero & García Carrascosa 2002), September ( Boero & Fresi 1986), and November ( Picard 1951a; Boero & Fresi 1986) in the western Mediterranean; from April to December in Salento waters (De Vito 2006; this study).

Medusa. Adult. Umbrella hemispherical during contraction, calotte-shaped or almost flat when relaxed; manubrium cruciform; mouth with 4 simple lips; gonads oval on distal half of radial canals; with up to 20–29 marginal tentacular bulbs; 28 statocysts, each with one statolith. Colours: bell transparent; gonads, manubrium, bulbs and tentacles assuming the colour of food.

Developmental stages. Newly released medusa with hemispherical umbrella; manubrium quadrate or laterally collapsed; 4 perradial and one ring canals; gonads on median region of radial canals; 4 perradial tentacular bulbs and 4 interradial developing bulbs; tentacles hollow, with a terminal nematocyst cluster; 4–8 adradial statocysts, each with one statolith.

Cnidome. A- and B-type microbasic mastigophores (hydroid); A-, C-, and D-type microbasic mastigophores and holotrichous isorhizas (medusa) (nematocyst nomenclature follows that of Östman, 1979a, b).

Distribution. Tropical and subtropical waters of Atlantic, Pacific and Indian oceans, Mediterranean Sea ( Yamada 1959; Millard 1975; Calder 1991; Ramil & Vervoort 1992; Medel & López-González 1996; Morri & Bianchi 1999; Peña Cantero & García Carrascosa 2002; Bouillon et al. 2004; Gravili et al. 2008a; Morri et al. 2009; Occhipinti-Ambrogi 2011; Soto Ãngel & Peña Cantero 2013; Bianchi et al. 2014).

Records in Salento. Common at: Torre S. Emiliano, Marina di Corsano, Ponte del Ciolo ( Presicce 1991); La Strea, S.ta Caterina, S.ta Maria al Bagno ( Denitto 1996; Miglietta et al. 2000); Otranto ( Denitto 1996; Miglietta et al. 2000; De Vito 2006; Gravili 2006; Andreano 2007; Gravili et al. 2008a; Stabili et al. 2011; Ventura 2011; Piraino et al. 2013; this study); Grotta del Ciolo (Denitto et al. 2007; Moscatello & Belmonte 2007); S. Maria di Leuca (Mastrototaro et al. 2010); Il Chiapparo (C. Gravili unpublished observations).

Remarks. The whole life cycle was examined in the present study. C. linearis is probably the first successful Lessepsian hydroid that colonized the Mediterranean Sea from the Suez Canal and, then from Gibraltar, expanded its distribution to the Atlantic coast of Spain (for more details see Boero et al. 2005).

References Picard & Le Roch (1949), Picard (1951a, b, 1952), Rossi (1961), Millard (1975), García-Corrales et al. (1978), Marinopoulos (1979) all as C. gravieri ; Boero (1981a, b, c), García Carrascosa (1981), Boero et al. (1985), Gili & García-Rubíes (1985), Boero & Fresi (1986), Gili (1986), Llobet et al. (1986, 1991), Roca (1986), Östman et al. (1987), Roca et al. (1991), Ramil & Vervoort (1992), Bianchi et al. (1993, 2014), Altuna (1994, 1995), Medel & López-González (1996), Migotto (1996), Morri & Bianchi (1999), Piraino et al. (1999), Miglietta et al. (2000), Lindner & Migotto (2002), Peña Cantero & García Carrascosa (2002), Bouillon et al. (2004), Touzri et al. (2004), De Vito (2006), Gravili (2006), Denitto et al. (2007), Galea (2007), Moscatello & Belmonte (2007), Gravili et al. (2008a), Morri et al. (2009), Puce et al. (2009), Gravili et al. (2010), Mastrototaro et al. (2010), Occhipinti-Ambrogi et al. (2011), Ventura (2011), Zenetos et al. (2011), Piraino et al. (2013).

Figures

FIGURE 103. Clytia linearis: A, colony; B, hydrotheca; C, diaphragm; D, gonotheca with two medusa buds; E, newlyreleased medusa; F, eight-tentacles stage, with mature gonads; G, 15 - tentacles stage with mature gonad (modified after Boero et al. 2005). Scale bars: A, 3.0 mm; B, D, 0.5 mm; C, F, G, 1.0 mm; E, 0.3 mm.