Obelia, Peron & Lesueur, 1810

Mendoza-Becerril, María A., Estrada-González, Mariae C., Mazariegos-Villarreal, Alejandra, Restrepo-Avendaño, Luisa, Villar-Beltrán, Rogelio D., Agüero, José & Cunha, Amanda F., 2020, Taxonomy and diversity of Hydrozoa (Cnidaria, Medusozoa) of La Paz Bay, Gulf of California, Zootaxa 4808 (1), pp. 1-37: 28-29

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Obelia   spp.

Figs. 11 View FIGURE 11 A –F

Material examined. Medusa—PB7_3, sampling site 1 (5), mature, three males and two females, 27ºC. PB7_12, sampling site 2 (14), one immature and 13 mature, six males and seven females, 27ºC. PB7_9, sampling site 3 (1), mature, male, 26.5ºC.

Description. Medusa—Umbrella flat, disc-like (0.6–1.2 mm wide), and reduced velum. Manubrium short, 0.2 mm long, with quadrangular base (0.2 mm wide), without peduncle, mouth with four simple lips. Circular canal and four radial canals narrow. Gonads spherical to ovoid, without median groove and peduncle, located on the medial or distal portion of radial canals (0.1 mm wide). Numerous solid marginal tentacles (34–76), each with a small endoderm extension into the mesoglea and small tentacle bulb. With eight closed ectodermal statocysts located under tentacle bulbs, each with a statolith.

Nematocysts (length x diam.). Isorhiza (3.4–4.6 x 1.6–3.1 µm), microbasic b-mastigophore (5.4–6.8 x 1.3–1.6 µm).

More detailed description Russell (1953) and Cornelius (1995).

Remarks. The general characters of these specimens agree with the diagnosis of medusae of Obelia Péron & Lesueur, 1810   . Our specimens varied in size, the number of marginal tentacles, and position of gonads, characters commonly related to ontogenetic variations ( Russell 1953; Cornelius 1995), hindering identification to the species level. Östman (1982b) showed that some species may present particular types of nematocysts, but these differences have not been further tested and adopted by subsequent authors.

Distribution. Genus cosmopolitan, present in all oceans ( Russell 1953; Cornelius 1995; Russell 1953). In Mexican Pacific, medusae of Obelia   have been registered from Baja California (Angel de la Guardia Island, Cedros Island, Punta Banda Estuary and Todos Santos Island) ( Fraser 1938a; Fraser 1938b; Fraser 1948), Baja California Sur (Bahía Concepción, Bahía de los Ángeles, Espíritu Santo Island, Natividad Island, Santa Maria Bay and Thurloe Bay) ( Fraser 1938a; Fraser 1938b; Fraser 1948; Aguirre & Bückle 1992; Palomares-García et al. 2002), Sonora (Rocky Point, Tiburón Island and locality not specified) ( Fraser 1948; Gómez-Aguirre 1991), Sinaloa (Mazatlán and locality not specified) (Álvarez-León 1978; Gómez-Aguirre 1991), Nayarit (Isabel Island and locality not specified) ( Fraser 1938a; Fraser 1938c; Gómez-Aguirre 1991), Jalisco and Colima (Clarion Island, Navidad Head, Socorro Island, Tenacatita Bay, and Teopa Beach) ( Fraser 1938a; Fraser 1948; Segura-Puertas et al. 2010; Lazo-Wasem et al. 2011; Gamero-Mora et al. 2015), Guerrero (Acapulco, Contramar, Morro de Patatlan, Morro Tierra and White Friars Islands) ( Fraser 1938a; Salcedo-Martínez et al. 1988; Guerrero-Ruíz et al. 2014; Gamero-Mora et al. 2015), and Oaxaca (Chacahua Bay, Corralero Bay, Mazuntle and Tangola-Tangola Bay and Santa Cruz Bay) ( Fraser 1938a; Fraser 1948; Humara-Gil & Cruz-Gómez 2018).