Sacculina carcini belongs to the group of parasitic barnacles known as the Rhizocephala, a bizarre group only recognisable as being barnacles by their cyprid larvae. As adults they have no hard external shell or limbs. The body is reduced to an interna of root-like absorptive filaments and the externa, a fleshy sac consisting of the reproductive structures. Sacculina carcini is an internal parasite of swimming crabs, characterised by a cream-brownish, oval externa. The mantle opening is slightly raised, small and placed almost opposite the stalk. The externa, reaching 2.5 cm in width, protudes from underneath the abdomen of the host.
Recorded distribution in Britain and Ireland
Recorded in the Shetlands, St Andrew's Bay, Cullercoats Coast, East Anglia, Dorset and Devon, north and south Wales, Morecambe Bay, Isle of Man, the west coast of Scotland, and near Belfast in Northern Ireland.
Found from Scandinavia South into the Mediterranean. Sacculina carcini has been introduced, along with its host Carcinus maenas, into Myanmar.
Sacculina carcini is found parasitising shallow water members of the swimming crab family (Portunidae) including Carcinus maenas, Liocarcinus holstatus, Liocarcinus depurator and Necora puber.
Externa roughly symmetrical.
Externa oval, with medial mantle opening, almost opposite stalk.
Found parasitising members of the swimming crabs (Portunidae), particularly Carcinus maenas.
Sacculina carcini produces long-lived cyprid larvae that survive in the plankton on their own food reserves and metamorphose into male and female larvae. Female and larger male larvae occur in the plankton throughout the year but with females predominating in summer and males in autumn and winter. Female larvae infect young crabs and develop inside the host for about 5 - 34 months before developing the externa. The externa contains ovaries that produce eggs that are fertilized by the male larvae. The parasite infects both male and female crabs, which results in thier castration, and prevents further molts. It causes the males to develop female characteristics. Host crabs may carry multiple infections of this parasite.
Hosie, A.M. 2008. Sacculina carcini Crab hacker barnacle. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 20-08-2018]. Available from: https://www.marlin.ac.uk/species/detail/2233
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