''Dermechinus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of sea urchin in the family Echinidae found in deep water in the southern Indian, Pacific and Atlantic Oceans. It is

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

, with ''Dermechinus horridus'', sometimes called the cactus urchin, being the only species.

Taxonomy

The species was first described in 1879 as ''Echinus horridus'' by the American zoologist Alexander Agassiz, after being dredged from the deep seabed during the

Challenger expedition The ''Challenger'' expedition of 1872–1876 was a scientific program that made many discoveries to lay the foundation of oceanography. The expedition was named after the naval vessel that undertook the trip, . The expedition, initiated by Wi ...

of 1872–1876. In 1942, it was allocated to the newly erected genus ''Dermechinus'' by the Danish zoologist Ole Theodor Jensen Mortensen, a specialist in sea urchins.

Description

An unusual-looking bright-orange sea urchin, ''Dermechinus horridus'' is globular when young but sometimes grows to a height more than twice its width. The fine long spines grow in vertical rows and are interspersed with a dense mat of shorter ones.

Pedicellaria A pedicellaria (plural: pedicellariae) is a small wrench- or claw-shaped appendage with movable jaws, called valves, commonly found on echinoderms (phylum Echinodermata), particularly in sea stars (class Asteroidea) and sea urchins (class Echi ...

e and

tube feet Tube feet (technically podia) are small active tubular projections on the oral face of an echinoderm, whether the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on br ...

are also present, and the general appearance of the sea urchin is similar to a cylindrical cactus.

Distribution

''D. horridus'' has a global but discontinuous distribution on the continental slope in oceans in the southern hemisphere; this includes Chile, South Africa, Australia and New Zealand. The depth range of this sea urchin is .

Ecology

This sea urchin tends to perch on rocks, in rows at right angles to the current, and has a relatively small mouth, leading to the speculation that it might be a filter feeder, an unusual feeding method among sea urchins. Commenting on this suggestion, sea urchin expert F. Julian Fell pointed out that ''Dermechinus horridus'' lived in

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

-rich waters and that its upright posture resembled that of a filter-feeding sea cucumber; the long spines formed combs and the short spines would be suitable for transporting small particles to the mouth at the base of the animal, with the tiny jaws adequate for ingesting them. So this feeding method is a possibility, but direct observation is needed.

References

{{Taxonbar, from=Q16628478 Echinometridae Taxa named by Ole Theodor Jensen Mortensen Monotypic genera