Monanthus ciocalyptoides n. sp. is described from two localities in the West Indian region, viz. the Saba Bank (17°25’N 63°33’W) and the Colombian Caribbean (11°20’N 74°09’W). The genus was hitherto known from South African waters only, by the type-species M. plumosus Kirkpatrick (1903). The systematic status of the new species and the genus as sublithistid members of the order Halichondrida is discussed.