E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Molpadia intermedia (Ludwig, 1894)
Sweet Potato Sea Cucumber
Family: Molpadiidae
Photo of species

© Aaron Baldwin  Email the photographer   (Photo ID #43635)

E-Fauna BC Static Map
Distribution of Molpadia intermedia in British Columbia
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Species Information

Click on the image below to view an expanded illustration for this taxon. If more than one illustration is available for a species (e.g., two subspecies may be illustrated) then links to the separate images will be provided below.

Molpadia intermedia has a smooth, sausage-shaped body that tapers abruptly to a short, appendix-like tail that is 20-25% of its body length. This species ranges in colour from a dark, purplish brown to purplish grey with rusty brown patches. Specimens collected with a dredge contract into plump sausages 11 to 14 cm in length. When relaxed and feeding, they can extend 35 to 43 cm in length. There are no tube feet on the smooth skin. The 15 tentacles - only 2 or 3 mm long - form a tight ring around the mouth. The stubby tentacles have a single pair of lateral branches just below the tip.

Skin ossicles: It is difficult to find ossicles in adult specimens. Reddish brown phosphatic bodies make up 99% of the deposits in the skin. Among the phosphatic bodies, and especially near the posterior end, there are a few variable tables, as illustrated in the figure. In juveniles there are clusters of racket-shaped plates radiating around a central table with a tall narrow spire (not shown).

Similar Species

There are no species similar to Molpadia intermedia in the shallow waters covered in this book.



intermedia = may mean intermediate

I have found no studies on the feeding habits of Molpadia intermedia. However, a similar species from the east coast, Molpadia oolitica, occurs vertically in the mud with its mouth pointing downward and its anus at the surface. Mud is eaten and forcibly expelled through the anus, forming a cone-shaped mound. M. intermedia may behave in a similar fashion.

Molpadia intermedia spawns from mid November to late December. Under study in a laboratory, females forcibly ejected negatively buoyant, orange-pink eggs of mean diameter at 267 μm from the gonopore at the anterior end. Males eject puffs of sperm over a period of 1.5 to 3 hours. The pelagic lecithotrophic larva settles out of the plankton after about 96 hours. In the laboratory, they are negatively phototactic. Early juveniles feed in the top few millimetres of mud with the mouth facing up.

The skin of M. intermedia is characterized by ovoid, reddish-brown granules made of some calcium and silica, but mostly a form of iron called ferric phosphate: hence the name phosphatic bodies. The granule content increases with age, and large specimens from shallow water have more. Researchers are not certain of the function of these granules.

The Sand Star (Luidia foliolata) preys on Molpadia intermedia.


Molpadia intermedia is common in soft sediments in many coastal inlets. It is found up to 35 cm below the surface of the mud, but only 5 to 8 cm in more firm mud. This species is dominant in some areas where it reaches a density of up to 15 per m². Individuals tend to aggregate in groups of two to six in an area of about 1 to 2 m².

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)
BC Ministry of Environment: BC Species and Ecosystems Explorer--the authoritative source for conservation information in British Columbia.

Synonyms and Alternate Names

Trochostoma intermedium Ludwig

Additional Range and Status Information Links

Additional Photo Sources

General References

Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2021. E-Fauna BC: Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. [Accessed: 2023-09-29 1:27:13 PM]
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