Marine Invertebrate of the Week: Sea Cucumber Crab

Lately, Cassidy and I have been finding cool marine invertebrates near the aquarium. During the REEF survey last week, I was surprised to find a little crab sitting on top of a sea cucumber. After doing some research, I discovered this crab is called a Sea Cucumber crab for its symbiotic relationship with sea cucumbers. The crab and cucumber exhibit a specific type of symbiotic relationship, commensalism. Commensalism is a relationship where one organism benefits while the other organism is unaffected by the relationship.

D. B. James in 1995 describes this unique relationship in his paper entitled “Animal associations in echinoderms”. James states that the crabs usually live in the tentacles or anus of the cucumber and only venture outside when the cucumber is dead.

Sea Cucumber crab (Lissocarcinus orbicularis)

Sea Cucumber crab (Lissocarcinus orbicularis)