''Pseudocentrotus depressus'', commonly known as the pink sea urchin, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of sea urchin, one of only two species in the genus ''Pseudocentrotus''. It was first described in 1864 by the American marine zoologist Alexander Agassiz as ''Toxocidaris depressus'', having been collected during the

North Pacific Exploring and Surveying Expedition The North Pacific Exploring and Surveying Expedition, also known as the Rodgers-Ringgold Expedition was a United States scientific and exploring project from 1853 to 1856. Commander Cadwalader Ringgold (1802–1867) led the expedition until ...

undertaken by Captain Cadwalader Ringgold and later Captain John Rodgers.

Description

This sea urchin is distinctive in its shape, with the oral (lower) surface being flat and the aboral (upper) surface markedly depressed in the centre. The tubercles are numerous and even in size, and the spines are fine and short, their diameter being about a quarter of their length. The inter-ambulacral plates are broad and the pore pairs are arranged in slightly curved groups of six or seven pairs.

Ecology

As is the case with most other sea urchins, the sexes are separate in this species, and adults liberate eggs and sperm into the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

. After fertilisation, the echinopluteus

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

e spend several months swimming and drifting with the

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

. Metamorphosis is stimulated by the detection by the larvae of suitable locations to settle on the seabed, cues being provided by the presence on the substrate of films of micro-algae or of microbes. In the absence of a suitable habitat, the larvae can continue swimming, but metamorphosis will eventually happen even in the absence of these cues.

Uses

''Pseudocentrotus depressus'' is used for human consumption and is the most important species of sea urchin in the southern Japan fishery.

References

{{Taxonbar, from=Q3199120 Strongylocentrotidae Edible shellfish Animals described in 1864