Psolus chitonoides 

Armored Sea Cucumber, Creeping pedal sea cucumber, slipper sea cucumber

Synonyms:  Psolus californicus
Phylum Echinodermata
 Class Holothuroidea
   Order Dendrochirotida
     Family Psolidae
Psolus chitonoides, about 6 cm long, found subtidally at Sares Head, WA. 
Photo by: Dave Cowles, July 2011
Description:  Looks much like a chiton, especially when the oral (buccal) tentacles are retracted.  Shape is like a cucumber that has been sliced in half lengthwise as the soft, orange ventral side is almost perfectly flat.  Ventral side is covered in tube feet.  Upper surface is covered with overlapping calcareous plates (resembling a chiton’s plates) (photo), which are usually a reddish-orange color.  The mouth is located on the upper surface some distance from the anterior end and is surrounded by 10 bright red oral tentacles of equal length.  Length to 7 cm.

How to Distinguish from Similar Species:  Psolidium bidiscum is more purplish in color and is smaller (only up to 3cm long).

Geographical Range:  Pribilof Islands and Gulf of Alaska to Baja California

Depth Range:  Low intertidal zone to subtidal depths of 247m

Habitat:  Rocks in exposed and sheltered inlets.

Biology/Natural History:  P. chitonoides is essentially sedentary.  The cucumber uses its ten equal tentacles to filter detritus from the water.  Sticky pads on each tentacle capture the food particles.  The tentacles contain toxic compounds called saponins to discourage fish from nibbling at them.  Predators that ignore these chemicals or are not affected by them include Stimpson’s Sun Star, the Northern Sun Star, the Leather Star, the Sunflower Star, and the Red Rock Crab.  The animals spawn in the spring and a large female may release up to 34,700 eggs.  The eggs form a lecithotrophic larvae followed by a pentacula larvae.  The larvae frequently settle in groups, usually on or near an adult.

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Dichotomous Keys:
  Carlton, 2007
  Flora and Fairbanks, 1966
  Kozloff, 1987
  Smith and Carlton, 1975

General References:
  Harbo, 1999
  Kozloff, 1993.
  Lamb and Hanby, 2005
  O’Clair and O’Clair, 1998.
  Ricketts et al., 1985
   Sept, 1999.

Scientific Articles:

Emlet, Richard B., 1994. Body forms and patterns of ciliation in nonfeeding larvae of echinoderms: functional solutions to swimming in the plankton? American Zoologist 34: pp. 570-585

Fankboner, P.V., 1978.  Suspension-feeding mechanisms of the armoured sea cucumber Psolus chitonoides Clark.  Journal of Experimental Marine Biology and Ecology 31: 11-25

McEdward, Larry R. and Benjamin G. Miner, 2006.  Estimation and interpretation of egg provisioning in marine invertebrates.  Integrative and Comparative Biology 46:3 pp 224-232

Young, C.M. and F-S Chia, 1982.  Factors controlling spatial distribution of the sea cucumber Psolus chitonoides:  Settling and post-settling behavior.  Marine Biology 69: 195-205

General Notes and Observations:  Locations, abundances, unusual behaviors, etc.:

Another photo of Psolus chitonoides.  Noted the scalelike plates the upper surface is covered in.  The buccal tentacles retract into the opening on the top right.
Photo by Dave Cowles, August 1997.  Total length about 5 cm.

This species has bright red oral tentacles, as seen in this underwater photo.  Note the animal on the right has a tentacle in the mouth to remove adhered material.
Photo by Jim Nestler, July 2005

This 4 cm individual was photographed by Kelly Williams in 2002

Authors and Editors of Page:
Kelly Williams (2002):  Created original page
Edited by Hans Helmstetler 12-2002, Dave Cowles 2005