The family Caecidae deserved special attention, among mollusks, because they occurred in more than 50% of studied stations in Oceanographic Operation Geomar XII, which was carried out in northern and southern coasts of Rio de Janeiro and Espírito Santo States (Brazil), respectively. At the time, Caecum brasilicum Folin, 1874, C. aff condylum Moore, 1969, C. circumvolutum Folin, 1867, C. johnsoni Winkley, 1908, C. someri Folin, 1867, C. striatum Folin, 1868, C. venosum Folin, 1867, C. floridanum Stimpson, 1851, C. massambabensis Absalão, 1994, C. butoti Jong & Coomans, 1989, C. ryssotitum Folin, 1867, C. nitidum (Stimpson., 1851) e C. cubitatum (Folin, 1868) were identitíed. C. venosum is reported, for the first time, since its original description, enlarging its occurrence area from Pernambuco to Rio de Janeiro; C. buloti as well, primarily restricted to Dutch Antilles, begins to make part of the Brazilian malacofauna. C. someri and C. butoti were pointed out for being largely non-sintopic with other congeneric species, suggesting that subtile differences in sediment can be responsable for this segregation.
Mesogastropoda; Caecidae; Caecum; taxonomy; geographic distribution; sintopy