Sacculina carcini

Geographic Range

Sacculina carcini is a parasitic species, so its geographic range follows its host. Carcinus maenas, the green crab, is a major host. The green crab is considered a highly invasive species, so it is not clear where S. carcini's actual range is. Carcinus maenas has a native range of the upper European/North African coast, though it has since spread to most of the major coasts, including the United States' New England coast area, the western U.S. coast, some areas at the southern coast of South America, the southern coast of Africa, and the southeast coast of Australia. In addition, S. carcini is being introduced in areas to control C. maenas, so it is possible that the parasite extends to some of the crab's invasive range. (Høeg, et al., 2000; Jones, 2007)


Sacculina carcini lives in a marine environment. During the brief larval period, S. carcini is pelagic, but as an adult, it lives as a parasite within a crab. The crabs that S. carcini prefers to parasitize live in coastal waters with mud, rock, or sand substrates. (Day, 1935; Foxon, 1940; Jones, 2007)

  • Range depth
    200 to 0 m
    656.17 to 0.00 ft

Physical Description

Sacculina carcini differs greatly from other barnacles. While the larval form is typical of the barnacle cypris larvae, the adult form is extremely reduced. At first, the female adult form resembles a microscopic slug, but as it parasitizes the crab, it grows tendrils that allow S. carcini to obtain nutrients from the crab's tissues. As it develops, it becomes more of an ovoid sack hanging off the parasitized crab, essentially nothing but a mass of reproductive tissue enclosed in chitinous armor. The male S. carcini is extremely small and serves only to fertilize the female's eggs. (Day, 1935; Takahashi and Lutzen, 1998; Zimmer, 2001)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range mass
    <1 (low) g
    (low) oz


The life cycle of S. carcini begins with a nauplius larvae being emitted from the mantle cavity of the host. The free-living nauplius larvae molts several times over five or six days, and then enters the cypris stage. Three days into the cypris stage, S. carcini attaches to its host's antenna. From there, it sheds its abdomen and thorax, and enters the crab as a mass of embryonic cells through its antennae. At this point, the mass of cells migrates to the mid-gut of the crab just below the heart and extends tendrils to secure itself and obtain nutrition. (Day, 1935)

Several weeks after it enters its host, Sacculina carcini extends a small knob through the abdomen of its host called an externa. This knob is where the male S. carcini enters the female. (Zimmer, 2000a)


The female S. carcini extends a small knob to the outside of a crab, through which a microscopic male larvae enters. Typically, a female S. carcini has two males which live off of it and constantly fertilizes it. The female then produces hundreds of eggs a day, which incubate in the abdomen of the host. (Zimmer, 2001)

A Sacculina carcini female is fertilized by microscopic males which live within it. The female releases fertilized eggs into the abdominal cavity of the host, where the eggs are incubated and develop into free-living larvae. About 6 weeks after finding a host, the young are capable of reproducing. (Foxon, 1940)

  • Breeding season
    On Carcinus maenas June or July to September, on Portunus holsatus the breeding season is short and in the early spring

While a female S. carcini provides no parental care, the hosts provide an efficient means of distribution for larvae. The behavior of both male and female infected crabs is modified so that they treat the externa from S. carcini like their own eggs. Infected crabs climb to high places with fast currents and disperse larval parasites like they would their own eggs, thus continuing the cycle of infection. At this point, the free-swimming S. carcini larvae are entirely independent.

  • Parental Investment
  • pre-hatching/birth


The lifespan of S. carcini is host-dependent, as its life-span matches that of the host. In many crabs this is 1-2 years. (Zimmer, 2000b)


Sacculina carcini spends the entirety of its mobile life as plankton. When it finds a suitable host, it extends tendrils throughout the host's body and becomes not much more than a mass of reproductive tissue. This parasite also modifies its host's behavior by causing infected male crabs to act as females, and to expand their abominable cavity. The host's behavior is also modified to treat S. carcini's eggs as if they were its own eggs. (Foxon, 1940)

Communication and Perception

The adult S. carcini is extremely reduced. Because the female consists, literally, of only its root-system of tendrils which allow it to draw nutrients and influence its host and the external reproductive sac, S. carcini lacks any real sensory perception. However, they aer able to locate a host through chemical perception. Adult males have enough sensory perception to presumably allow it to find a female. (Day, 1935; Zimmer, 2001)

Food Habits

Sacculina carcini is entirely parasitic, relying on its host for nutrition. Its host secretes nutrients, which it absorbs. (Zimmer, 2000a)

  • Animal Foods
  • body fluids


Because S. carcini is an internal crab parasite, its only predators are animals that predate on crabs.

Ecosystem Roles

Sacculina carcini is a parasite on a wide variety of crab species, and causes decreased fertility in infected crabs. Since Carcinus maenas is a primary host, S. carcini works to somewhat control the green crab population. Currently S. carcini is being considered whether it is an effective invasive species regulatory control. In some populations, S. carcini can render up 50% of the crab population infertile, so in theory, S. carcini can have an important effect on the ecosystem balance. (Høeg, et al., 2000; Zimmer, 2000a)

Species Used as Host
  • Carcinus maenas
  • Carcinus aestuarii
  • Blue-leg swimming crab, Liocarcinus depurator
  • Toothed permiela, Perimela denticulata
  • Portunidae species

Economic Importance for Humans: Positive

Sacculina carcini has been considered as a means of controlling invasive crab species, but due to low host specificity it also seems to damage non-invasive crab populations. As such, it is not yet known whether or not S. carcini will be an appropriate invasive species control. (Høeg, et al., 2000)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Sacculina carcini causes economic damage to humans by decreasing the viability of crabs harvested for human consumption. Crabs infected with S. carcini cease molting, and so do not grow to a suitable size for eating. Carcinus maenas in particular is considered to be of gastronomic importance, and is frequently eaten in many European countries. (Høeg, et al., 2000; Jones, 2007)

Conservation Status

Sacculina carcini does not have any conservation status.


Winnie Jeng (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.


Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

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Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

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living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.


union of egg and spermatozoan


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death


An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).


Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).

radial symmetry

a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season


non-motile; permanently attached at the base.

Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa


reproduction that includes combining the genetic contribution of two individuals, a male and a female


uses touch to communicate


Boxshall, G. 2009. "Sacculina carcini Thompson, 1836" (On-line). WoRMS - World Register of Marine Species. Accessed April 23, 2011 at

Day, J. 1935. The life-history of Sacculina. Quarterly Journal of Microscopical Science, s2 (77): 549-583. Accessed May 01, 2011 at

Foxon, G. 1940. Notes on the life history of Sacculina carcini Thompson. Journal of the Marine Biological Association of the United Kingdom, 24 (1): 253-264. Accessed May 02, 2011 at

Glenner, H., M. Hebsgaard. 2006. Phylogeny and evolution of life history strategies of the parasitic barnacles (Crustacea, Cirripedia, Rhizocephala). Molecular Phylogenetics and Evolution, 41 (3): 528-538.

Glenner, H., M. Werner. 1998. Increased susceptibility of recently moulted Carcinus maenas (L.) to attack by the parasitic barnacle Sacculina carcini Thompson 1836. Journal of Experimental Marine Biology and Ecology, 228 (1): 29-33.

Høeg, J., N. Murphy, C. Wittwer. 2000. Developing the options for managing marine pests: specificity trials on the parasitic castrator, Sacculina carcini, against the European crab, Carcinus maenas, and related species. Journal of Experimental Marine Biology and Ecology, 254 (1): 37-51.

Jones, T. 2007. "Carcinus maenas" (On-line). Accessed March 16, 2010 at

Lützen, J. 1981. Field studies on regeneration in Sacculina carcini Thompson (Crustacea: Rhizocephala) in the Isefjord, Denmark. Journal of Experimental Marine Biology and Ecology, 53 (2-3): 241-249.

Payen, G., M. Hubert, Y. Turquier, C. Rubiliani, C. Chassard-Bouchaud. 1981. Infestations expérimentales de crabes juvéniles par la sacculine. Ultrastructure des racines parasitaires en croissance et relations avec la niasse ganglionnaire ventrale de l'hôte (Experimental infestations of young Carcinus With Sacculina carcini). Canadian Journal of Zoology, 59: 9.

Russell, J., G. Walker, R. Woollen. 2000. Observations on two infectious agents found within the rootlets of the parasitic barnacle, Sacculina carcini. Journal of the Marine Biological Association of the UK, 80: 373-374.

Takahashi, T., J. Lutzen. 1998. Asexual reproduction as part of the life cycle in Sacculina polygenea (Cirripedia: Rhizocephala: Sacculinidae). Journal of Crustacean Biology, 18 (2): 321-331.

Zimmer, C. 2000. Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creature. New York, New York: Touchstone.

Zimmer, C. 2001. "Animal Parasites" (On-line). Science World. Accessed April 23, 2011 at

Zimmer, C. 2000. "Do Parasites Rule the World?" (On-line). Discover Magazine. Accessed April 23, 2011 at