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Phylum NEMERTEA – nemerteans, nemertines - page 5 / 6





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Common name: 'Mophies, barnacles

Agent / classification: Rhizocephalan barnacles (Cirripedia). Locally: Loxothylaxus panopei in mud crabs (introduced from Gulf), Loxothylacus texanus in blue crabs (Gulf), Sacculina spp.

Host: Decapods: crabs, shrimp, some oddballs in other crustaceans.

General problem: Probably the bizarrest of the bizarre! High prevalences in certain locations 40-75%.  High salinity disease for the most part (in blue crabs).

Life cycle:

Free living thoracican: adult – egg – nauplius – cypris – settlment and growth to adult

Rhizo: sacculina externa – egg – nauplius – cypris – (kentrogon) – vermigon – sacculina interna

Female is the externa, male is the cypris. Interna settles around midgut, ramfies throughout host. Last host molt, externa breaks through and effectively mimics egg clutch.

Crabs infected during ecdysis. Cypris is negatively phototactic, negatively barotactic.

Pathology:  Parasitic castrators, feminizers of males. Phenotype issue.

Cessation of molting so small crabs result from infections.

Castration effected through (1) physical destruction of gonad, (2) resource competition for reproductive products, or (3) physiological drain on host's metabolic resources.

Partial or complete (but castrated) feminization results from destruction of androgenic gland (male gland). AG causes maleness in crustaceans.  Behavioral shifts in male crabs. They become more like females (including copulatory embraces).

Population costs: castrated individuals. hidden cost due to matings with sterile males and females. Observed as infertile egg clutches.

Transmission: direct but convoluted life cycle. Transmission via planktonic stages.

Diagnosis /  Identification:  Sacculina externa is a dead giveaway. Sacculina internae can be observed in midgut and nerve preparations.  Taxonomy difficult. For the most part, derived from host lists.

Treatment: None, removal of sac can kill hosts. Those that recover, lose infection.

Control: Primarily a fishery problem. Cull locally, destroy culls, implement collection and disposal program for fishery but hampered by infected "shorts."

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