Abstract: The present invention is directed to the isolation and bioactive characterization of compounds isolated from the clam Spisula polynyma. These compounds include three sphingoid-type bases, spisulosines 285, 299 and 313 (1-3), each of which shows unique cytotoxicity against L1210 murine lymphocytic leukemia cells. In addition, sphingosine (also referred to as 4-sphingenine or octadeca-4-shpingenine, 4) and two related compounds, nonadeca-4-sphingenine (a one carbon longer homolog, 5) and sphinga-4,10-diene (a dehydrosphingosine deravitive, 6) were also obtained, These compounds also contribute to the cytotoxicity of the Spisula polynyma extracts, but did not cause the morphology changes observed with compounds 1-3.