New species of Caecum (Caenogastropoda: Rissooidea: Caecidae) from the Atlantic coast of South America (Brazil) with a description of the protoconch and growth stages.

Two new species of Caecinae are described from the Brazilian coast. Specimens of Caecum metamorphosicum sp. nov. were collected from northern to southeastern Brazil. The teleoconch V of this species is characterized by strong, raised, quadrangular, rather closely arranged axial ribs, except the last two to three preceding the aperture, which are slightly larger and more widely separated, and a finger-shaped mucro. Specimens of Caecum trindadense sp. nov. were only collected from southeastern Brazil. The teleoconch VI of this species is characterized by conspicuous, sinuous longitudinal striae, finger-shaped mucro, and rather smooth varix. The protoconch and all growth stages of C. metamorphosicum sp. nov. and C. trindadense sp. nov. are described and figured here based on scanning electron microscopy. A brief discussion on the biodiversity of Caecidae on the Atlantic coast of South America is given. This report provides a basis for the better recognition of growth stages among members of Caecinae.