The Echinoid Directory

Biology and geological history of the Cidaroida


Cidaroids are exclusively epifaunal and use their powerful lantern for scavanging and preying on sessile organisms (sponges, stalked crinoids, etc.) or algae. They move over the surface by means of their oral spines and often have highly ornamented ambital and aboral spines. Their spines are not covered in epidermis as in other echinoids, but are exposed with an external cortex of calcite, and thus are commonly encrusted with algae and epizoans. This provides them with excellent camouflage from predators, as well as a first line of defence.

Most cidaroids pass through a planktotrophic stage in development, but there are a minority of taxa which are lecithotrophs, producing a small number of large yolky eggs that develop directly. These show sexual dimorphism in the relative size of the gonopores between males and females, and some may even develop marsupia for brooding.

Today cidaroids are most common in deeper shelf or continental slope settings, extending down to abyssal depths. Shallower water forms live in more protected habitats such as back-reef, lagoonal or perireefal environments where wave surge is not strong (they lack oral phyllodes and thus have weak grip). Their distribution in the past is likely to have been very similar.

Diet for three species of cidaroid has been documented by Jacob et al. (2003) and reviewed in De Ridder & Lawrence (1982). Modern cidaroids have been observed to prey on the stalks of isocrinid crinoids (Baumiller et al. 2008).

Baumiller, T. K., Mooi, R. & Messing, C. G. 2008. Urchins in the meadow: paleobiological and evolutionary implications of cidaroid predation on crinoids. Paleobiology 34, 22-34.

Jacob, U., Terpstra, S. & Brey, T. 2003. High-Antarctic regular sea urchins - the role of depth and feeding in niche separation. Polar Biology 26, 99-104.

De Ridder, C. & Lawrence, J. M. 1982. Food and feeding mechanisms: Echinoidea. In M. Jangoux & J. M. Lawrence (eds) Echinoderm Nutrition. A. A. Balkema, Rotterdam.

Geological History

The earliest fossil that can be unambiguously assigned to the Cidaroida is Eotiaris from the late Lower Permian. This has both a well developed perignathic girdle of apophyses and U-shaped teeth whose detailed ultrastructure is identical to that of modern cidaroids (Smith & Hollingworth, 1990). Relatively few cidaroids are known from the Triassic, but from the Jurassic onwards they are represented in almost all fossil echinoid communities.

Smith, A. B. & Hollingworth, N. T. J. 1990. Tooth structure and phylogeny of the Upper Permian echinoid Miocidaris keyserlingi. Proceedings of the Yorkshire Geological Society 48, 47-60.