''Halocynthia igaboja'', commonly known as the sea hedgehog, the bristly tunicate or spiny sea squirt, is a species of

tunicate A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ca ...

in the family

Pyuridae Pyuridae is a family of tunicates.Gittenberger, A.; Sanamyan, K. (2015)Pyuridae.In: Shenkar, N.; Gittenberger, A.; Lambert, G.; Rius, M.; Moreira Da Rocha, R.; Swalla, B.J.; Turon, X. (2015) Ascidiacea World Database. Accessed through: World Regis ...

. It is native to the northeastern Pacific Ocean. This species was first described in 1906 by the Japanese marine biologist Asajiro Oka, who gave it the name ''Cynthia ritteri''. It was later transferred to the genus ''

Halocynthia ''Halocynthia'' is a genus of ascidian tunicates in the family Pyuridae. Species such as '' H. roretzi'' are used as food. Species within the genus ''Halocynthia'' include:Sanamyan, K. (2015)''Halocynthia'' Verrill, 1879 .In: Shenkar, N.; Gitte ...

''.

Description

Solitary tunicates like the sea hedgehog have a roughly globular body with a leathery body wall or tunic, and two siphons. The buccal siphon draws water into the body, and the atrial siphon expels water. In this species, the tunic is dark brown but is rendered almost invisible by the numerous large, branching, spine-like processes which cover it. The longest spines bear rings of recurved secondary spines. The siphons are often reddish or orangish in colour; the buccal siphon is at the top of the animal and is surrounded by twelve to fifty

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s, while the atrial siphon is a third to half of the way down the body. At a maximum height of and width of , this is one of the largest solitary tunicates in the

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though ...

. It could be confused with the cactus sea squirt (''Boltenia echinata'') but is altogether spinier and larger.

Distribution and habitat

The sea hedgehog is found in Japan, southeastern Asia, and the Pacific Coast of North America, from Alaska to California. It prefers rocky or gravelly

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s with vigorous currents, with a depth range from the intertidal down to about .

Ecology

The sea hedgehog is a

suspension 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 ...

, drawing water through its body and filtering out the

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

and organic material.

Detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

and

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

s tend to accumulate on the spiny processes when the current is weak, rendering the animal almost invisible. The spines act as a defence against the Oregon hairy triton, a gastropod mollusc. The bristly sea squirt '' Boltenia villosa'', lives in the same habitat but is less spiny; it defends itself by becoming an epibiont and preferentially settling on the spines of the sea hedgehog. This species is a semi-gregarious species and is cannibalistic, consuming its own eggs and larvae.

References

{{Taxonbar, from=Q4912293 Stolidobranchia Animals described in 1906