This form has not been studied at Woods Hole. If the masses are kept in running sea water, the eggs develop readily. The gelatinous material is transparent and faintly yellow in color. Fertilization apparently takes place before the eggs are laid. Cleavage is total, equal and spiral, with micromeres larger than those of L. Iittorea or L. saxatilis.
Gastrulation is by epiboly and invagination.
The veligers have a foot, operculum, single-whorled shell, kidney, ganglia, and a complex gut. At the time of emergence from the capsule, the larvae are fully-formed, crawling snails. The ova of L. obtusata are plentiful and relatively easy to study. The genus Littorina in the western Atlantic. Entwicklungsgeschichte von Littorina obtusata.