Nematopsis

The genus name Nematopsis is derived from the worm resembling sporozoite. Nematopsis: “resembling a nematode”. == History of knowledge ==

Nematopsis was first described by A. Schneider in France in 1892. Due to N. portunidarum’s (previously known as N. schneideri) ovoid oocysts, Schneider initially assigned the species to the Coccidia. However, in 1903 Leger found similar spores in mussels and proposed the name Nematopsis schneider. These spores germinated into vermiform sporozoites resembling small nematode worms, hence the name Nematopsis. In 1911 Leger and Dubosq proposed the new name Porospora portunidarum after the same spores hatched in the crab Portunus and developed into a gregarine. However in 1931 Hatt changed the classification back to Nematopsis after observing its resistant monozoic spores; he renamed it Nematopsis portunidarum. After Nematopsis’ initial discovery in 1892, Schneider also named another genus, Porospora, in 1875. These two genera make up the family Porosporidae Labbe 1899. For many years following the discovery of these two genera, their taxonomic differences were unclear and confusing. This description was used as criteria on which to assign species to the genus. Most species were described after 1938. In 1938, Ball described the genus Carcinoecetes, a parasite of crabs which was initially thought to be related to the family Prosporidae. However, members of Carcinoecetes are now accepted as belonging to either Nematopsis or Cephaloidophora. Three previously described Carcinoecetes species are now considered Nematopsis: N. calappae, N. Hesperus and N. matutae. == Habitat and ecology ==

Nematopsis is a marine parasite which utilizes marine bivalves as intermediate hosts. They have been found all over the world; including United States, India, Thailand, Spain, Brazil and other coastal regions. The primary host of Nematopsis are the mud and stone crabs. Gutierrez- Salazar et al. (2011) suggest that Nematopsis sp. was most prevalent in morning and evening temperatures. Due to the endo-parasitic nature of Nematopsis other factors such as water quality and presence of bacteria did not influence its abundance. == Description ==

Morphology and anatomy In general, adult extracellular Nematopsis (sporadins) are milky-white in color, and associate as groups of two caudo-frontally, with one cell's anterior side contacting the other's posterior. The two cells are associated linearly and range from around 150-200 μm in length. The gametocyst of Nematopsis, the cyst in which gametes are produced in gregarines, is spherical and around 110-160 μm in diameter. At the sporozoite rostral end there is an oval nucleus, rough endoplasmic reticulum, mitochondria and secretory granules. The oocyst of Nematopsis contains a single uni-nucleated vermiform sporozoite. The oocysts is encapsulate in a thick hyaline wall. Life cycle Crustacean host Nematopsis undergoes growth, gametogenesis, sexual recombination, and zygote formation in its crustacean host (i.e. crab) and produces gymnospores that go on to infect molluscan hosts. Genetics Little genetic material of Nematopsis has been sequences. Ribosomal RNA of Nematopsis temporariae was sequenced to show its parasitic relationship to tadpoles. == Practical importance ==

As Nematopsis infects molluscs and crustaceans, it has strong effects on aquaculture. Recent studies have been conducted to investigate the role of Nematopsis as a parasite in commercially valuable marine organisms, in particular bivalves and crustaceans. Gregarine disease of penaeid shrimp is a common disease caused by Nematopsis spp. that affects shrimp in the United States, France, and India. Due to parasite attachment in the crustaceans gut lumen, reduced absorption of food and intestinal blockages can occur in the host. Similarly to crustacean, molluscs with severe Nematopsis infections can develop lesions and hypertrophy which can lead to mechanical deformations inhibiting feeding and gas exchange, again resulting in poor quality shellfish and lower yields. Although Nematopsis infection may not always be severe, it is clear that it can affect aquaculture practice of both wild and cultured organisms and it is important to understand what influences the occurrence of Nematopsis infection and its severity. Better understanding of Nematopsis infection in commercially valuable species will lead to better management programs and optimization of quality and quantity of the desired aquaculture product. == Species list ==

Species are classified based on their host and oocyst morphology, little molecular data exists on the genus. ==References==