Crab hacker barnacle (Sacculina carcini)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help



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.

Global distribution

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.

Depth range


Identifying features

  • Externa roughly symmetrical.
  • Externa oval, with medial mantle opening, almost opposite stalk.
  • Found parasitising members of the swimming crabs (Portunidae), particularly Carcinus maenas.

Additional information

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.

Listed by

- none -



    1. Bristol Regional Environmental Records Centre, 2017. BRERC species records recorded over 15 years ago. Occurrence dataset: accessed via on 2018-09-25.

    2. Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset accessed via on 2018-09-25.

    3. Fife Nature Records Centre, 2018. St Andrews BioBlitz 2015. Occurrence dataset: accessed via on 2018-09-27.

    4. Fife Nature Records Centre, 2018. St Andrews BioBlitz 2016. Occurrence dataset: accessed via on 2018-09-27.

    5. NBN (National Biodiversity Network) Atlas. Available from:

    6. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2024-04-25

    7. Yorkshire Wildlife Trust, 2018. Yorkshire Wildlife Trust Shoresearch. Occurrence dataset: accessed via on 2018-10-02.


    This review can be cited as:

    Hosie, A.M. 2008. Sacculina carcini Crab hacker barnacle. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 25-04-2024]. Available from:

    Last Updated: 23/12/2008