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Pseudocnus curatus (Cowles, 1907)
Brooding Sea Cucumber
Family: Cucumariidae
Extracted from Sea Cucumbers of British Columbia, Southeast Alaska and Puget Sound by Philip Lambert.
Introduction to the Echinoderms of BC

Photograph

© Royal BC Museum     (Photo ID #2322)

Map

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Distribution of Pseudocnus curatus in British Columbia in British Columbia

Illustration

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Species Information

Pseudocnus curatus is a small, black sea cucumber about 1 to 3 cm in length. Its mouth and anus are slightly upturned; and its body tends to be a bit flattened. The tube feet are like scattered pits on the dark, dorsal surface, rather than being in rows. Ten equal-sized tentacles surround the mouth. The lighter-coloured ventral tube feet are usually more robust and in rows. The dorsal colour is a solid black or dark brown.

Skin ossicles: four-holed buttons with smooth wavy edges, some with more than four holes. Three-armed rods in the tube feet.

Similar Species

The identity of Pseudocnus curatus has been confused for a number of years. This species was described from California and until recently was thought to be found only around the Monterey region. It has been confused with Cucumaria pseudocurata, which is also black and intertidal. The latter has rows of tube feet on the dorsal side rather than being scattered; and it usually has eight large tentacles and two small ventral ones. Both species can occur on the same beach within a few feet of each other, so are often confused. To be certain of identification, one must look at the ossicles in the skin. Compare the ossicles of P. curatus with those of C. pseudocurata. The former has compact four-holed buttons and three-armed rods, the latter has oval, perforated plates.

P. curatus (=C. curata) has also been confused with P. lubricus (=C. lubrica). Most references identify the small black aggregating species found subtidally in high current areas of Juan de Fuca Strait as C. lubrica. This appears now to be incorrect (Arndt et al. 1996). Studies of the two species' ossicles and most recently, mitochondrial DNA, have shown that what used to be identified as C. lubrica is actually P. curatus. The true P. lubricus is also a brooding species that aggregates, but usually varies from white to brown with black specks on the dorsal side. Do not confuse it with Cucumaria piperata, which has black spots all over its body. P. curatus has smooth buttons while P. lubricus has more bumpy, lobed buttons. These two species are closely related and show about a 7% difference in their mitochondrial DNA.

Biology

Etymology

curata = to care for, referring to its brooding behaviour
Biology

Cowles (1907) described many individuals forming black patches just below the low tide mark, clinging tightly to the rocks. As soon as the eggs are laid, the mother transfers them to the ventral surface: here, they develop directly into juveniles. The eggs are about 1 mm in diameter when laid. Associated with this species during the breeding season is a small nematode that feeds on the eggs, often destroying the whole brood. A paper by Engstrom (1974) on the biology of C. lubrica probably describes Pseudocnus curatus (Cowles). The following biology is from several papers that used the name C. lubrica. In the summer months, it feeds on particulate matter with its extended tentacles. No feeding occurs from October to March and females do not feed while brooding eggs. The diet is mostly single-celled algae.

Animals spawn from mid November to mid December around southern Vancouver Island. Males lift the anterior end off the substratum and release long strands of white sperm from genital papillae located between two of the dorsal tentacles. Sperm sink to the substratum and become entangled in the bodies of other sea cucumbers. Females raise the anterior end of the body off the substratum and arch backwards. Eggs are then spawned and roll down onto the female's ventral surface between her tube-feet. The tentacles are not used to catch the eggs; thus, many can be washed away by the current. The female then re-attaches to the rock, holding the eggs against the substratum. The large eggs (mean 973 μm) are brooded from January to March. Six weeks after spawning young cucumbers hatch, but stay with the female for another four to eight weeks.

Many species of sea stars eat P. curatus: Sand Star (Luidia foliolata), three species of sunstars (Solaster stimpsoni, S. dawsoni, S. endeca), Leather Star (Dermasterias imbricata), Six-armed Star (Leptasterias hexactis) and the Sunflower Star (Pycnopodia helianthoides). The Saddleback amphipod (Parapleustes) has been observed eating eggs. Unlike some other sea cucumbers, P. curatus does not show an escape response to any of the sea stars.

Presumably as a camouflage, adult P. curatus often attach pieces of shell, wood and other material to its dorsal surface. P. curatus' body wall is toxic to certain fish such as gunnels, Apodichthys and Pholis: a strong defence mechanism against these predators.

The parasitic gastropod, Thyonicola mortenseni, infects Pseudocnus curatus.

Habitat


Pseudocnus curatus occurs on rocky intertidal and shallow subtidal rock in strong current or open coast surf. In California I have found it nestled in crevices in small groups sometimes partly overgrown with encrusting coralline algae on exposed rock. It may occur subtidally there, but perhaps few people have looked for this species in those exposed locations. In Juan de Fuca Strait it tends to be shallow subtidal in areas where the tidal currents are strong. They nestle together in large aggregations on open rocky surfaces.

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)		COSEWIC
UnlistedUnlistedUnlistedUnlisted



BC Ministry of Environment: BC Species and Ecosystems Explorer--the authoritative source for conservation information in British Columbia.

Synonyms and Alternate Names

Cucumaria curata Cowles

Additional Range and Status Information Links

Ocean Biogeographic Information System Distribution Map

General References

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