''Dermechinus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...

in the family

Echinidae Echinidae is a family of sea urchins in the order Echinoida. Members of the family are found in the Atlantic Ocean and the Antarctic.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 "unispec ...

, 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 Alexander Emmanuel Rodolphe Agassiz (December 17, 1835March 27, 1910), son of Louis Agassiz and stepson of Elizabeth Cabot Agassiz, was an American scientist and engineer. Biography Agassiz was born in Neuchâtel, Switzerland and immigrated to ...

, 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 Wil ...

of 1872–1876. In 1942, it was allocated to the newly erected genus ''Dermechinus'' by the Danish zoologist

Ole Theodor Jensen Mortensen Ole Theodor Jensen Mortensen, also known as Theodor Mortensen (22 February 1868 – 3 April 1952) was a Danish scientist and professor at the Zoological Museum, Copenhagen. He specialized in sea urchin Sea urchins () are spiny, globular echino ...

, 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 Echinoi ...

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 britt ...

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 Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

, 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 Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothuria ...

; 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