Sacculina
Sacculina is a genus of barnacles that is a parasitic castrator of crabs. They belong to a group called Rhizocephala. The adults bear no resemblance to the barnacles that cover ships, whales, and piers; they are recognised as barnacles because their larval forms are like other members of the barnacle class Cirripedia. The prevalence of this crustacean parasite in its crab host can be as high as 50%.
Habitat
Sacculina live in a marine environment. During their larval stage they are pelagic, but as they form into adults they live as ectoparasites on crabs. Their primary host is the green crab, which is native to the Eastern Atlantic Ocean. Though these crabs have spread to other bodies of water, it is not believed that Sacculina barnacles have traveled with them to these new localities.
Anatomy
The body of the adult parasite can be divided into two parts: one part is called the "externa" where the bulbous reproductive organ of the parasite sticks out of the abdomen of the host. The other part is called the "interna" which is inside the host's body. This part is composed of root-like tendrils that wrap themselves around the host's organs, which gives its group name of Rhizocephala, meaning "root-head". Through microCT scans, these roots have been discovered to wrap around certain organs of the body, with most around the hepatopancreas of crustaceans. This area is primarily for absorbing nutrients, which would explain why most concentrate in that region. In a similar species called Briarosaccus roots were seen extending to the brain and central nervous system, which is a hypothesis to help explain how parasites like these can manipulate their hosts' behavior.
Life cycle
The female Sacculina larva finds a crab and walks on it until she finds a joint. She then molts into a form called a kentrogon, which then injects her soft body into the crab while her shell falls off. The Sacculina grows in the crab, emerging as a sac, known as an externa, on the underside of the crab's rear thorax, where the crab's eggs would be incubated. Parasitic Sacculina destroy a crab's genitalia, rendering the crab permanently infertile.
After this invasion of the Sacculina, the crab is unable to perform the normal function of molting. This results in a loss of nutrition for the crab, and impairs its overall growth. The natural ability of regrowing a severed claw that is commonly used for defense purposes is therefore lost after the infestation of Sacculina.
The male Sacculina 'larva' looks for a female Sacculina on the underside of a crab. He then implants his cells into a pocket in the female's body called the "testis", where the male cells then produce spermatozoa to fertilize eggs.
When a female Sacculina is implanted in a male crab, it interferes with the crab's hormonal balance. This sterilizes it and changes the bodily layout of the crab to resemble that of a female crab by widening and flattening its abdomen, among other things. The female Sacculina then forces the crab's body to release hormones, causing it to act like a female crab, even to the point of performing female mating dances. If the parasite is removed from the host, female crabs will normally regenerate new ovarian tissue, while males usually develop complete or partial ovaries instead of testes.
Although all energy otherwise expended on reproduction is directed to the Sacculina, the crab develops a nurturing behavior typical of a normal female crab. The natural hatching process of a crab consists of the female finding a high rock and grooming its brood pouch on its abdomen and releasing the fertilized eggs in the water through a bobbing motion. The female crab stirs the water with her claw to aid the flow of the water. When the hatching larvae of Sacculina are ready to emerge from the brood pouch of female Sacculina, the crab performs a similar process. The crab shoots them out in pulses, creating a large cloud of Sacculina larvae. The crab uses the familiar technique of stirring the water to aid in flow.
Life span
Sacculina are primarily host dependent so their life span matches that of their hosts. Crabs usually have a life span anywhere from 1 to 2 years.
Sacculina has been suggested to be used as a type of biological control agent to help reduce the populations of the invasive green crab. This is controversial because Sacculina can also use native crab species as their host and there would be no way to control or stop them from attacking native species.
Species
More than 100 species of Sacculina are currently recognised:Sacculina abyssicola Sacculina actaeae Sacculina aculeata Boschma, 1928Sacculina ales Kossmann, 1872Sacculina americana Reinhard, 1955Sacculina amplituba Phillips, 1978Sacculina anceps Boschma, 1931Sacculina angulata Sacculina anomala Boschma, 1933Sacculina atlantica Boschma, 1927Sacculina beauforti Boschma, 1949Sacculina bicuspidata Boschma, 1931Sacculina bipunctata Kossmann, 1872Sacculina boschmai Reinhard, 1955Sacculina bourdoni Boschma, 1960Sacculina brevispina Sacculina bucculenta Boschma, 1933Sacculina bursapastoris Kossmann, 1872Sacculina caelata Boschma, 1931Sacculina calappae Sacculina calva Boschma, 1933Sacculina captiva Kossmann, 1872Sacculina carcini Thompson, 1836Sacculina carpiliae Sacculina cartieri Kossmann, 1872Sacculina cavolinii Kossmann, 1872Sacculina comosa Boschma, 1931Sacculina compressa Boschma, 1931Sacculina confragosa Boschma, 1933Sacculina cordata Shiino, 1943Sacculina crucifera Kossmann, 1872Sacculina curvata Boschma, 1933Sacculina cuspidata Boschma, 1949Sacculina dayi Boschma, 1958Sacculina dentata Kossmann, 1872Sacculina docleae Huang & Lützen, 1998Sacculina duracina Boschma, 1933Sacculina echinulata Sacculina elongata Boschma, 1933Sacculina eriphiae Smith, 1906Sacculina exarcuata Kossmann, 1872Sacculina fabacea Shiino, 1943Sacculina flacca Boschma, 1931Sacculina flexuosa Kossmann, 1872Sacculina gerbei Sacculina ghanensis Boschma, 1971Sacculina gibba Boschma, 1933Sacculina glabra Sacculina globularis Boschma, 1970Sacculina gonoplaxae Sacculina gordonae Boschma, 1933Sacculina gracilis Boschma, 1931Sacculina granifera Boschma, 1973Sacculina granulosa Boschma, 1931Sacculina guineensis Boschma, 1971Sacculina hartnolli Boschma, 1965Sacculina herbstianodosa Sacculina hirsuta Boschma, 1925Sacculina hirta Boschma, 1933Sacculina hispida Boschma, 1928Sacculina holthuisi Boschma, 1956Sacculina hystrix Sacculina ignorata Boschma, 1947Sacculina imberbis Shiino, 1943Sacculina inconstans Boschma, 1952Sacculina infirma Boschma, 1953Sacculina inflata Leuckart, 1859Sacculina insueta Boschma, 1966Sacculina irrorata Boschma, 1934Sacculina jamaicensis Boschma, 1966Sacculina lata Boschma, 1933Sacculina leopoldi Boschma, 1931Sacculina leptothrix Boschma, 1933Sacculina lobata Boschma, 1965Sacculina loricata Sacculina margaritifera Kossmann, 1872Sacculina micracantha Boschma, 1931Sacculina microthrix Boschma, 1931Sacculina muricata Boschma, 1931Sacculina nectocarcini Sacculina nigra Shiino, 1943Sacculina nodosa Boschma, 1931Sacculina ornatula Boschma, 1951Sacculina ostracotheris Boschma, 1967Sacculina papposa Sacculina pertenuis Boschma, 1933Sacculina phacelothrix Boschma, 1931Sacculina pilosa Kossmann, 1872Sacculina pilosella Sacculina pinnotherae Shiino, 1943Sacculina pisiformis Kossmann, 1872Sacculina pistillata Boschma, 1952Sacculina pomum Kossmann, 1872Sacculina pugettiae Shiino, 1943Sacculina pulchella Boschma, 1933Sacculina punctata Boschma, 1934Sacculina pustulata Boschma, 1925Sacculina quadrialata Boyko & van der Meij, 2018Sacculina rathbunae Boschma, 1933Sacculina reinhardi Sacculina reniformis Boschma, 1933Sacculina robusta Boschma, 1948Sacculina rotundata Miers, 1880Sacculina rugosa Sacculina scabra Boschma, 1931Sacculina schmitti Boschma, 1933Sacculina scutigera Huang & Lützen, 1998Sacculina semistriata Sacculina senta Boschma, 1933Sacculina serenei Boschma, 1954Sacculina setosa Sacculina spectabilis Boschma, 1948Sacculina spinosa Sacculina striata Boschma, 1931Sacculina sulcata Sacculina surinamensis Boschma, 1966Sacculina teres Boschma, 1933Sacculina teretiuscula Boschma, 1931Sacculina ternatensis Boschma, 1950Sacculina upogebiae Shiino, 1943Sacculina vankampeni Boschma, 1931Sacculina verrucosa Sacculina vieta Boschma, 1933Sacculina weberi Boschma, 1931Sacculina zariquieyi Boschma, 1947