Sacculina are a type of barnacle that parasitises crabs. They belong to the genus Rhizocephala. Barnacles are pelagic in the larval stage, but when they develop into adults, they live on the crab as an ectoparasite. The mature parasite body is divided into two parts, one of which is called the "external" and contains the parasite's bulbous genitalia (Figure 1), which protrude from the host's abdomen. The other part is known as the "internal body" and is located inside the host. The roots of Briarosaccus have been observed to reach into the brain and central nervous system, thereby affecting the host's behaviour.
Figure 1. The external part of Sacculina.
How it infects the crabs?
Upon finding a crab, the female Sacculina larvae walk on the crab until they find the joints and inject them into the crab. When the female Sacculina are implanted in the male crab, the male crab's hormonal balance is disrupted. The crab's abdomen will widen and flatten, thus sterilising the male crab, and the body shape will change to resemble that of the female crab. Other than that, it has been observed that male crabs will even perform female-specific mating manoeuvres when induced by females.
How to diagnose Sacculina’s infected crab?
There is study found that the mud crab species most infected with Sacculina is S. olivacea as compared to other species. Clinical signs can be used to diagnose whether a crab is infected with Sacculina. Figure 2 shows that the carapace of infected crabs is wider and fatter than that of uninfected crabs. In addition, the abdomens of infected and uninfected crabs are different. The abdomen of infected crabs was turned to be like female crabs (Figure 3). Another clinical sign of infected crabs is the size of the claws, which are smaller compared to normal crabs (Figure 4). The most obvious clinical sign of an infected crab is the observation of the outer portion of the Sacculina on the abdomen.
Figure 2. Different shapes of crab’s carapace
Figure 3. Different shapes of crab’s abdomen
Figure 4. Different sizes of claw
Treatment of Rhizocephala barnacles of crab
Currently, there is no treatment other than removal of the parasite from the host. The method of removing the parasite is also important as removal by cutting is not recommended as this can result in the death of the crab. A common method of parasite removal is to twist the exterior of the Sacculina so that it becomes less attached and detaches from the crab. In addition to removing the parasite from the host, prophylaxis is one of the best ways to prevent widespread transmission of the parasite. Isolation of infected crabs from other crabs is one way to prevent other crabs from contracting Sacculina, which is transmitted by water.
References
Hazlehurst, K. and McKeever, C. 2023. Which parasite has the weirdest way of life? Natural History Museum. Retrieved on 2 June 2023 from https://www.nhm.ac.uk/discover/which-parasite-has-the-weirdest-way-of-life.html
Jeng, W. 2011. "Sacculina carcini" (On-line), Animal Diversity Web. Retrieved on 2 June 2023 from https://animaldiversity.org/accounts/Sacculina_carcini/
Waiho, K., Fazhan, H., Glenner, H. and Ikhwanuddin, M. 2017. Infestation of parasitic rhizocephalan barnacles Sacculina beauforti (Cirripedia, Rhizocephala) in edible mud crab, Scylla olivacea. PeerJ, 5, p.e3419.
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