Cassiduloida

Article By:

Mooi, Rich Department of Invertebrate Zoology and Geology, California Academy of Sciences, San Francisco, California.

Last reviewed:October 2019

DOI:https://doi.org/10.1036/1097-8542.900669

The name originally given by C. Claus in 1880 to what is now recognized as an unnatural (nonmonophyletic) group of echinoids (sea urchins) containing the lamp urchins. There are only about 30 extant species of cassiduloids (that is, members of the Cassiduloida). These are sometimes referred to as “living fossil” holdovers of a group that was far more diverse in the Mesozoic and Cenozoic eras. Today, specialists recognize four main subgroups: Echinolampadidae, Cassidulidae, Apatopygidae, and Neolampadidae. The echinolampadids and apatopygids have been placed closer to the order Clypeasteroida (sand dollars and relatives) than to the other cassiduloid groups, strongly suggesting that the cassiduloids are not monophyletic. The echinolampadids (notably the genus Echinolampas) have a resemblance to ancient oil lamps when the animal is held upside-down, therefore leading to the vernacular name: lamp urchins. Like all sea urchins, the body, or test, of cassiduloids (see illustration) is made up of a radiating series of columns of adjoined plates. The test of cassiduloids is unlike that of “regular” echinoids in being strongly bilaterally symmetric, with the anus at the posterior end. Sometimes the anus is situated slightly toward the top (aboral surface) of the test and leads to a shallow channel, or sulcus. The mouth is located near the center of the bottom, or oral, surface, with each of the five tube-foot-bearing ambulacra (the radial series of plates) modified into specialized phyllodes near the mouth. In between the phyllodes are slight swellings called bourrelets which bear dense clumps of spines. See also: Clypeasteroida; Echinodermata; Echinoidea; Irregularia; Regularia

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