Spawn morphology and subsequent development are described and illustrated from laboratory observations for two species of marine prosobranch gastropods, Cerithium alucaster (Brocchi, 1814) and Euspira fusca (Blainville, 1825). The spawn of C. alucaster consisted of a white and amorphous, irregularly coiled string. The egg capsule had a mean diameter of 155 mm. Shell dimensions of the free-swimming larvae at hatching were 130 mm length and 90 mm height. The appearance of the protoconch I and the beginning of protoconch II surface was smooth, as seen with scanning electron microscopy. The spawn of E. fusca had a flat ribbon shape, coiled to form an incomplete circle. Eggs were spheroidal in shape, with a mean major diameter of 396 mm and were placed in two layers. Development was direct. Shell dimensions at hatching were 276 mm length and 196 mm heigth. The protoconch was smooth with granular spiral lines on its dorsal part. The spawn of each species was similar to the general pattern exhibited by other species of their respective families.