Amoebae cultured from seawater collected at a coastal site near Barbados were largely a lobose amoeba with long tapered subpseudopodia identified as Vexillifera telmathalassa. Vexillifera telmathalassa occurs widely in marine environments and additional information is presented here on its hue structure, salinity tolerance, and feeding behavior toward clarification of its taxonomic characteristics and ecological niche. The amoebae were able to adjust to a gradual decline in salinity from 36% to 16 parts per thousand, but at a salinity of 12 parts per thousand. They all became immobilized and discoidal. The fine structure showed a centrally located nucleus (2.1 mu m) with a prominent nucleolus. The plasma membrane is coated with glycostyles 17 nm long and 14 nm apart, and may be derived from secretory vesicles with similar glycocalyx lining. Bacteria and occasional eukaryotic remains occur in digestive vacuoles or membrane-enclosed spaces. Some vacuoles (2.0-2.5 mu m) are filled with scattered masses of digested material and resemble the ''glanzkorper'' previously identified by light microscopy. In addition to bacterial prey, microflagellates were also ingested in laboratory culture as observed by light microscopy. Vexillifera telmathalassa may be more closely linked trophically to the microbial loop than previously recognized.
