User:Bmassey98/sandbox

Appearance
The Sacculina carcini differ greatly between males and females. The female barnacles look like small slugs before they reach the carb. Once they have infected inside of a host, they begin to develop and grow tendrils that allow it to get the nutrients that it needs from the crab. Eventually, it can be seen hanging off the crab's abdomen filled with reproductive tissue. The male parasites serve a different purpose. They are very small and serve only to help the females reproduce.

Distribution and Habitat
S. carcini is a monoxenic parasite. This means that is only had one definitive host. The most common host being the green crab (Carcinus maenas). Other hosts can be Carcinus aestuarii, Liocarcinus depurator (Harbour crab), Perimela denticulata, and Necora puber (Velvet crab). This parasite's habitat is largely based on where its hosts can be found. It is primarily found in costal water around rock, sand, and mud. It generally stays in more shallow water. Geographically, S. carcini can be seen in Western Europe and North Africa. Since the species of crab's that is parasitizes has started to spread, it can be found in most major coasts, including North America, South America, Southern Africa, and Australia.

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 (bristle). It then develops into a form called a kentrogon, which inserts a stylet into the crab and pushes its way inside. To do this, she sheds her outer hard shell. 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. It takes 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 gonads, which eventually degrade; 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 pleopods 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 takes place and they develop ovarian tissue.

The eggs inside the externa are fertilised 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.

Human Impacts
Sacculina carcini is known to control the population size of the Green crab by making many of them infertile. Without reproduction, the population can not expand and can cause a shortage for human consumption. The parasite also causes the crabs to stop molting once infected, therefore the crab does not always grow to a size big enough for eating.