A juvenile of the Atlantic species, Arbacia
punctulata
Sea urchins are a useful model system for studying many problems in early development. Historically, sea urchins were a key model system in elucidating a variety of classic developmental problems, including the mechanisms of fertilization and egg activation, cleavage, gastrulation, and the regulation of differentiation in the early embryo. In addition, early studies of the the molecular basis of early development were carried out in this system. Gametes can be obtained easily, sterility is not required, and the eggs and early embryos of many commonly used species are beautifully transparent. In addition, the early development of sea urchin embryos is highly synchronous, i.e., when a batch of eggs is fertilized, all of the resulting embryos typically develop on the same time course. This makes biochemical and molecular studies of early embryos possible in this system, and has led to a number of major discoveries.