A genus of SEA URCHINS in the family Echinometridae. They are closely related to and some say indistinguishable from the genus Heliocidaris.
Sea Urchins
Somewhat flattened, globular echinoderms, having thin, brittle shells of calcareous plates. They are useful models for studying FERTILIZATION and EMBRYO DEVELOPMENT.
Ovum
A mature haploid female germ cell extruded from the OVARY at OVULATION.