''Sacculina carcini'', the crab hacker barnacle, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of parasitic barnacle in the family Sacculinidae, in particular a parasitic castrator, of

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

s. The crab that most often is used as a

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 ...

is the

green crab ''Carcinus maenas'' is a common littoral crab. It is known by different names around the world. In the British Isles, it is generally referred to as the shore crab, or green shore crab. In North America and South Africa, it bears the name europ ...

, the natural range of which is the coasts of Western Europe and North Africa. It can be found attached to the crab's abdomen and affect consumption rates by humans.

Appearance

The ''Sacculina carcini'' differ greatly between males and females. The female barnacles look like small slugs between entering the crab and infecting it. Once they have infected their host, they begin to develop and grow tendrils. This allows them to get the nutrients that it needs from their host. Over time, it can be seen hanging off the crab's abdomen filled with reproductive tissue. The male parasites are much smaller and serve only to help the female ''Sacculina carcini'' reproduce.

Distribution and habitat

''Sacculina carcini'' is a monoxenic parasite of crabs, most commonly the

(''Carcinus maenas''). They have also been found to infect the ''Carcinus aesturarii, Liocarcinus depurator (''Harbour crab), ''Pirimela denticulata,'' ''Necora puber'' (Velvet crab), and the ''Liocarcinus holsatus'' (Flying crab). The parasite's range largely coincides with that of this host, which is usually the coasts of Western Europe and North Africa. The green crab, however, has been expanding its range and has become established in both North and South America, Southern Africa and Australia, so it is possible that the parasite is now present outside its natural territory. These crabs all live in shallow water over sandy, rocky, or muddy substrates.

Life cycle

A female ''Sacculina carcini'' larva settles on a suitable crab host and crawls across its surface until it finds a suitable spot such as the base of a

seta In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. Th ...

(bristle). It then develops into a form called a ''kentrogon'', which inserts a stylet into the crab and pushes its way inside. In order to do this, she has to shed her outer hard shell first. From there it moves through the inside of the crab, in due course pushing out a sac, known as an ''externa'', on the underside of the crab's abdomen. The part remaining inside, the ''interna'', develops tendrils which spread throughout the crab. They take over the stomach, intestines, and nervous system to absorb nourishment and enable the parasite to control the behavior of its host. The presence of the parasite inhibits the development of the crab's

gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...

s, which eventually atrophy; it also prevents the crab from molting, consequently preventing it from regenerating lost limbs. The parasite causes a male crab to develop certain feminine characteristics including the broadening of its abdomen, while in females, the abdomen becomes narrower and the

pleopod The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various ...

s degenerate. The eggs of the parasite develop in the externa and both male and female crabs carry these eggs around, secured under their abdomen, in the way that female crabs normally care for their own brood (but males never do). If the parasite is experimentally removed from the host, female crabs will usually regenerate their ovaries, but in males,

sex change Sex change is a natural or artificial process in which an individual's sex is changed. Sex change may also refer to: Biology and medicine *Sex reassignment therapy *Sex reassignment surgery *Sequential hermaphroditism, a phenomenon whereby some ...

takes place and they develop ovarian tissue. The eggs inside the externa are fertilized by male larvae which enter the sac through a pore. These males are tiny, never become adults and soon die. However, the female, including the externa, can live for as long as the crab host survives, perhaps one or two years. Hundreds of eggs are produced every day and remain in the sac for about six weeks. When the parasite eggs are ready for release, the crab will climb onto a rock, bob about to release them and waft them on their way. The cycle then continues with each generation.

Organism impacts

The ''Sacculina carcini'' is known to control the population size of their hosts, like the Green crab, by making many of them infertile. Without reproduction, the population cannot expand and can cause a shortage for human consumption. The parasite can also cause their hosts to stop molting once infected. This can cause the crab to stop growing before it reaches a size big enough for human consumption.

References

External links

* {{Authority control Barnacles Crustaceans described in 1836 Crustaceans of the Atlantic Ocean Mind-altering parasites Parasitic crustaceans Parasites of crustaceans