Gnesioceros sargassicola (Mertens, 1833)

Planaria sargassicola Mertens, 1833: 13–14, pl. 1, figs 4–6 (type locality: Sargasso Sea 20° N – 24° N, 30° W – 76° W).

Stylochus mertensi Diesing, 1850: 216 (Atlantic Ocean between 21°– 35° N and 36°– 38°W) (description).

Stylochus pelagicus Moseley, 1877: 23 (description).

Stylochus sargassicola – Ehrenberg 1836: 67 (description).

Planocera sargassicola – Örsted 1844: 48 (description).

Gnesioceros mertensi – Diesing 1862: 571 (description).

Stylochoplana sargassicola – Graff 1892: 207–213, pl. 9 figs 1–5 (description).

Pelagoplana sargassicola – Bock 1913: 306 (description).

Gnesioceros sargassicola – Hyman 1939a: 146 (new record, common in the Gulf of Mexico, Caribbean, and North Atlantic). — Marcus & Marcus 1968: 48–51, figs 45–49 (description and new record from Piscadera Bay, Curacao, Brazil; Puerto Rico, Florida, Central Atlantic Ocean). — Cheng & Lewin 1975: 518 (new record, on the surface of the sea near La Paz, Baja California Sur, Mexico). — Faubel 1983: 119–121, figs 38a–c, 39 (description and new record from Caribbean Sea, Sargasso Sea 20°N – 42°N, 30°W – 76°W). — Prudhoe 1989: 69 (review). — Hooge & Newman 2009: 417 (review). — Cuadrado et al. 2021: 32–33, fig. 7l (description and new record from Gran Canaria Island and Tenerife Island, Canaria Islands).

Distribution

Cosmopolitan distribution. Bermuda; Gulf of Mexico; Caribbean Sea; La Paz Bay, Baja California Sur; off West African coast (21°– 35° N, 36°– 38° W) (Mertens 1832); off West African coast (9°21′ N, 18°25′ W and 5°48′ N, 14°20′ W) (Moseley 1877); West Africa and Madeira (Graff 1892); dredged in about 2 meters at Boa Vista, Cape Verde Island (Laidlaw 1906).

Habitat

Epibiont (commonly found on Sargassum C.Agardh, Halimeda J.V.Lamouroux, Rhizophora L., Thalassia Banks ex König and Ulva L.); coastal surface and epipelagic; pelagic (neustal, hyponeustal organism), associated with Halobates Eschscholts, 1822; or benthic (sandy bottom).

Remarks

This polyclad is common on Sargassum and is found on floating weeds in various parts of the world. Marcus & Marcus (1968) recorded it as an epibiont species on seaweeds of the genera Halimeda, Rhizophora, Thalassia, and Ulva . They also associated it with habitats such as sandy bottom, sandy shore with reef debris, and sandy flat with Cymodocea K.D.König and Thalassia .

Cheng & Lewin (1975), using zooplankton samples, identified a pelagic polyclad species in the Bay of La Paz, Baja California Sur, which they named G. sargassicola . However, their record is considered questionable in this study due to the lack of a detailed description of the specimens.