''Carcinonemertes errans'' is a

ribbon worm Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of 1300 known species. Most ribbon worms are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. Many h ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Carcinonemertidae. It lives in

symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

with the

Dungeness crab The Dungeness crab (''Metacarcinus magister'') is a species of crab inhabiting eelgrass beds and water bottoms along the west coast of North America. It typically grows to across the carapace and is a popular seafood. Its common name comes from ...

(''Metacarcinus magister''), consuming the crab's developing eggs. In 1980 it was implicated in the collapse of the Dungeness crab fishery in central California.

Ecology

The planktonic larva of the worm settles on a suitable crab

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman * Michel Host ...

and encysts on the exoskeleton. ''Carcinonemertes errans'' is the first species in its genus to be found on a single host species. The worm has a permanent

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

relationship with its host crab but it is not a parasite as it does not feed directly on the crab but is instead an egg-predator. In male crabs, and in non-breeding female crabs, the worm may live in the axils of the limbs and encyst. After mating, the mature female crab stores the sperm for several months, before releasing a batch of fertilised eggs onto her abdomen, where she tucks them under the tail flap. At this stage, the ribbon worm migrates to the mass of eggs and feeds on the developing

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

s. If the worm larvae happen to settle on the exoskeleton of a brooding female crab, they can move immediately to the underside of the abdominal flap and

metamorphose Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some insec ...

within 48 hours into juvenile worms. When settling, the larvae are gregarious, settling preferentially on already infected crabs. It has been found that the worm is adversely affected by a lowering of the water salinity. Crabs in estuaries show an estuarine gradient, with crabs nearest the ocean carrying more worms than those further upstream.

Effect on the Dungeness crab industry

The Dungeness crab industry is an important fishery on the Pacific coast, with worth $170 million being harvested in 2014. In 1980, the central California fishery was badly affected; ''Carcinonemertes errans'' was implicated, with 50% of the crabs' eggs produced each year being predated.

References

{{Taxonbar, from=Q1995299 Monostilifera Animals described in 1978 Fauna of the Pacific Ocean Parasites of crustaceans