Obelia dichotoma (Linnaeus, 1758)

Estrada-González, Mariae C., Agüero, José & Mendoza-Becerril, María A., 2023, Medusozoans from the Mexican Pacific: a review based on historical literature and recent observations, Journal of Natural History 57 (1), pp. 784-853 : 834-835

Obelia dichotoma (Linnaeus, 1758)

( Figure 8E–G )

Material examined

3 colonies, polyp, with gonophores; Punta Diablo, La Paz Bay, Baja California Sur, 24.316°N, 110.340°W; depth 0–1 m; 7 May 2017; on ascidian, the coral Tubastrea coccinea coccinea , and rock; ECO-CH-Z 11750. – 2 colonies, polyp, with gonophores; Punta Los Muertos, Baja California Sur, 24.248°N, 110.150°W; depth 1–2 m; 20 July 2018; on the algae Chondria arcuata and Dyctiota concresens; ECO-CH-Z 11763. – 6 colonies, polyp, with gonophores; Agua de Yepiz, La Paz Bay, Baja California Sur, 24.288°N, 110.630°W; depth 0–1 m; 24 June 2018; on the alga Sargassum sp. , coralline algae, other undetermined algae, ascidian, barnacles, and Bryozoa; ECO-CH-Z 11787. – 1 colony, polyp, with gonophores; Punta El Coyote, Concepción Bay, Baja California Sur, 26.721°N, 111.909°W; depth 0–1 m; 23 July 2018; on nylon rope; ECO-CH-Z 11783. – Several colonies, polyp, without gonophores; El Mogote Sand Bar, La Paz Bay, Baja California Sur, 24.159°N, 110.341°W; depth 0–2 m; 1 July 2019; on undetermined algae, ascidian, and hydrocaulus of Clytia linearis and Pennaria disticha ; ECO-CH-Z 11795.

Identification (after Cornelius 1990; Calder 1991)

Colonies erect; hydrocaulus monosiphonic, sympodial, branched, divided into internodes, annulated basally, each supporting a pedicel distally and distal alternating apophysis. Hydrothecal pedicels annulated throughout. Hydrothecae campanulate, with nearly straight walls, margin entire and slightly flared. Hydrothecal diaphragm oblique. Gonothecae arising either from hydrothecal apophysis or hydrothecal pedicel, truncate distally with a tubular neck. Gonothecal pedicels annulated throughout.

Distribution

Previously recorded on the west coast of the Gulf of California ( Aguirre-Hinojosa and Bückle-Ramírez 1992; Mendoza-Becerril et al. 2020) and for the rest of the gulf in Sonora ( Brusca 2020). In the MP, it has been recorded in Baja California, Guerrero, Jalisco, and Oaxaca ( Fraser 1938a, 1948; Humara-Gil and Cruz-Gómez 2018; Brusca 2020; Mendoza-Becerril et al. 2020).

Remarks

The traditional concept of O. dichotoma (cf. Cornelius 1995) comprises multiple cryptic lineages ( Calder 2013; Calder et al. 2014; Cunha et al. 2017, 2020). However, the taxonomic determination was based on previous descriptions in the MP ( Mendoza-Becerril et al. 2020).

Superorder SIPHONOPHORAE Eschscholtz, 1829

Figures

Figure 8. A, Clytia cf. gracilis (M. Sars, 1850): hydrotheca. B, Clytia hemisphaerica (Linnaeus, 1767): hydrotheca. (C, D) Clytia linearis (Thornely, 1900): C, colony; D, hydrotheca. (E–G) Obelia dichotoma (Linnaeus, 1758): B, hydrothecae; C, colony; D, gonothecae from apophysis; E, gonothecae from hydrorhiza. Scale bars: A, B, D = 250 μm; C = 1 cm; F, G = 200 μm; E = 500 μm. Drawings made by Nicholas Bezio.