A new glycosyl inositolphosphoceramide-type ganglioside, CSP2, was obtained from the polar lipid fraction of the chloroform/methanol extract of the feather star Comanthina schlegeli together with a known same type of ganglioside CJP2. The structure of this ganglioside has been determined on the basis of chemical and spectroscopic evidence to be 9-O-methyl-(N-acetyl-α-D-neuraminosyl)-(2→3)-inositolphosphoceramide, which contains C₁₆-sphingosine and C_22:0-, C_24:0-fatty acid as major component. This is the first report on the isolation and structural elucidation of a glycosyl inositolphosphoceramide-type ganglioside possessing N-acetyl-neuraminic acid (NeuAc) residue.