Top image: The embryo of Echinaster brasiliensis (a starfish) is imaged with darkfield microscopy (60x magnification) at the 2-cell and 4-cell stages (top). The cells divide asymmetrically to form the morula (bottom left) and then differentiate into a swimming larva after gastrulation (bottom right).

Bottom image: The non-feeding larvae of the E. brasiliensis are called brachiolaria. In the late brachiolaria (bottom), the arms and adhesive disk are quite conspicuous and well-developed, whereas in the early brachiolarian larvae (top right) arms and adhesive disks are just starting to be visible. An elongated gastrula stage is shown in the upper left.

By Alvaro Esteves Migotto, Universidade de Sâo Paulo