Gnesioceros sargassicola

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.