Development of Cerithiopsis gemmulosum (Gastropoda: Cerithiopsidae) from Bocas del Toro, Panama

—The relationships between the seven families in the Ptenoglossa and the relationships between the Ptenoglossa and other gastropod groups have been based on anatomical features associated with feeding, and on developmental characters. However the embryonic development of several of these families remains undescribed. Here I describe the development of Cerithiopsis gemmulosum from Bocas del Toro Province, Panama. This species lives on and lays its thin-walled egg capsules in Halichondria melanadocia sponges. The 79 μm eggs have equal cleavage with a polar lobe. The ciliated “trochophore” stage is followed by an encapsulated veliger which has distinct embryonic kidneys and large granular cells that cover the head vesicle. The black eyes are large and develop early, but there is no pigmented mantle organ. At hatching the brown larval shell is a single whorl and 127 μm long, and each semicircular velar lobe is unpigmented. The velar lobes are equal in size at hatching, but as the shell grows and becomes high-spired the right lobe grows to twice the size of the left lobe. The late larval shell is smooth but has a prominent beak flanked by two distinct notches that fit the velar lobes. After 3 weeks in culture the velum begins to shrink, and larvae with 500 μm shell length metamorphose when exposed to host sponge.