ABSTRACT
Early development of the brooding sea-urchin Abatus cordatus: a new type of gastrulation.
Early development of Abatus cordatus takes place in brood-pouches over a 2 month interval. Cleavage which lasts 26 days (± 8 days), is partial and superficial during the initial 2 weeks. Thereafter, it is completed quickly, resulting in a wrinckled stereoblastula (without blastocoel). Gas-trulation lasts 39 days (± 10 days). It is characterized by migration of yolk-like elements in the space between the two outermost membranes (the fertilization membrane lasts until the end of early development) when the archenteron is differentiated. These yolk-like elements are produced at the oral pole of the embryo and closed the blastopore. At the end of gastrulation, the apical ectoderm differentiates the oral cavity of the embryo (similar to the echinian plate).
