Brooding in echinoderms: How can modern experimental techniques add to our historical perspective?

Echinoderms are among the most abundant and ecologically successful groups of marine animals on earth. Their unique adaptations have enabled them to inhabit diverse environments ranging from various substrates in shallow water habitats to the benthos of the deepest seas. Although members of the Echinodermata generally share common characteristics including radial symmetry, a unique water vascular system, and decentralized cephalization, they have evolved a variety of life history strategies that enable them to reproduce successfully across a wide range of habitats. These reproductive strategies range from a complete lack of parental care (broadcasting) to internal and external brooding of the eggs, embryos, and juvenile phases. Although brooding is relatively rare in echinoderms, it is of interest as a “deviant” or “derived” form of reproduction that has been the subject of much study and debate. The aim of the present review is to examine how and why brooding occurs from a historical perspective, and then explore how modern experimental techniques are providing novel approaches to answering fundamental questions related to brooding in this very successful group of benthic marine invertebrates.