''Clypeaster japonicus'', the Japanese sea biscuit, is a species of

sea urchin Sea urchins or urchins () are echinoderms in the class (biology), class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of . They typically have a globular body cove ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Clypeasteridae. This species was first

scientifically described A species description is a formal scientific description of a newly encountered species, typically articulated through a scientific publication. Its purpose is to provide a clear description of a new species of organism and explain how it diffe ...

in 1885 by the German zoologist Ludwig Heinrich Philipp Döderlein.

Description

This is a large species with a strong

test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film) ...

, growing to a maximum length of around . In shape it is an elongated pentagon, the aboral (upper) surface slightly higher at the apex than at the margins. The length of the petaloid area amounts to two thirds or more of the total length of the test. The anterior petal is open distally while the two posterior, paired petals are closed distally. The oral (under) surface is fairly flat, but deeply concave around the mouth, with conspicuous, but short, indented food grooves. The

anus In mammals, invertebrates and most fish, the anus (: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the ''exit'' end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facil ...

is on the oral surface near the posterior margin. The primary spines are rather longer than the densely felted secondary spines. When alive, this species is a uniform brown colour apart from the petals, which are a darker brown. The bare test is grey or pale brown.

Distribution

This sea biscuit is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to Japanese waters. Its range extends from northern

Honshu , historically known as , is the largest of the four main islands of Japan. It lies between the Pacific Ocean (east) and the Sea of Japan (west). It is the list of islands by area, seventh-largest island in the world, and the list of islands by ...

southwards to southern

Kyushu is the third-largest island of Japan's Japanese archipelago, four main islands and the most southerly of the four largest islands (i.e. excluding Okinawa Island, Okinawa and the other Ryukyu Islands, Ryukyu (''Nansei'') Ryukyu Islands, Islands ...

. Its depth range is from .

References

{{Taxonbar, from=Q2505086 Animals described in 1885

japonicus This list of Latin and Greek words commonly used in systematic names is intended to help those unfamiliar with classical languages to understand and remember the scientific names of organisms. The binomial nomenclature used for animals and plants ...