There are two species of sea anemone occurring on the floating sea weed Sargassum natans in the Caribbean sea: Bunodeopsis pelagica (Quoy & Gaimard) and Anemonia sargassensis Hargitt. The anemones are readily distinguished from one another by their colour and the nature of their tentacles. B. pelagica is pale brown with a characteristic ring of violet colour around the mouth; the tentacles are long and rough due to the presence of batteries of nematocysts along their lengths. A. sargassensis is darker brown, often with white or creamy yellow radiating markings on the oral disc. The tentacles are smooth, medium length and are very adhesive. They are usually irregular in arrangement and are 54-60 in number. In B. pelagica they are regularly arranged with the larger ones in the inner cycle, are usually in multiples of 6 and 12-36 in number. The tentacles are retractile in B. pelagica but not so in A. sargassensis. Both species are found on Sargassum natans, but occasionally A. sargassensis occurs in shallow water on Thalassia testudinum and on rocks along the shoreline.