| Saccosporidae | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Cnidaria |
| Class: | Malacosporea Canning, Curry, Feist, Longshaw & Okamura, 2000 |
| Family: | Saccosporidae Canning, Okamura & Curry, 1996 |
| Genera | |
Saccosporidae is a family of myxozoans. [1] [2] It is the only family within the class Malacosporea and has only three species, while the other class of Myxozoa, Myxosporea, includes more than a thousand.
Saccosporidae are parasites of fish and freshwater bryozoans. Tetracapsuloides bryosalmonae, the only representative of the group whose life cycle is well studied, causes proliferative disease of the kidneys in salmonids. Two stages of the life cycles of the two species in the genus Buddenbrockia are known. One of them is a saccular stage, similar to Tetracapsuloides. During the second stage the animals are mobile and superficially resemble minute worms. Buddenbrockia allmani parasitizes Lophopus crystallinus , while Buddenbrockia plumatellae parasitizes, in particular, Plumatella fungosa .
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has characterised parasites as "predators that eat prey in units of less than one". Parasites include single-celled protozoans such as the agents of malaria, sleeping sickness, and amoebic dysentery; animals such as hookworms, lice, mosquitoes, and vampire bats; fungi such as honey fungus and the agents of ringworm; and plants such as mistletoe, dodder, and the broomrapes. There are six major parasitic strategies of exploitation of animal hosts, namely parasitic castration, directly transmitted parasitism, trophically transmitted parasitism, vector-transmitted parasitism, parasitoidism, and micropredation.
Plasmodium is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of Plasmodium species involve development in a blood-feeding insect host which then injects parasites into a vertebrate host during a blood meal. Parasites grow within a vertebrate body tissue before entering the bloodstream to infect red blood cells. The ensuing destruction of host red blood cells can result in disease, called malaria. During this infection, some parasites are picked up by a blood-feeding insect, continuing the life cycle.
Myxozoa is an unranked subphylum of aquatic, obligately parasitic cnidarian animals and contains the smallest animals ever known to have lived. Over 2180 species have been described and some estimates have suggested at least 30,000 undiscovered species. Many have a two-host lifecycle, involving a fish and an annelid worm or a bryozoan. The average size of a myxosporean spore usually ranges from 10 μm to 20 μm, whereas that of a malacosporean spore can be up to 2 mm. Myxozoans can live in both freshwater and marine habitats.
Trematoda is a class within the phylum Platyhelminthes. It includes two groups of parasitic flatworms, known as flukes.
Myxosporea is a class of microscopic parasites, belonging to the Myxozoa clade within Cnidaria. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate and an ectothermic vertebrate, usually a fish. Each host releases a different type of spore. The two forms of spore are so different that until relatively recently they were treated as belonging to different classes within the Myxozoa.
Digenea is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms with a syncytial tegument and, usually, two suckers, one ventral and one oral. Adults commonly live within the digestive tract, but occur throughout the organ systems of all classes of vertebrates. Once thought to be related to the Monogenea, it is now recognised that they are closest to the Aspidogastrea and that the Monogenea are more closely allied with the Cestoda. Around 6,000 species have been described to date.
Coccidia (Coccidiasina) are a subclass of microscopic, spore-forming, single-celled obligate intracellular parasites belonging to the apicomplexan class Conoidasida. As obligate intracellular parasites, they must live and reproduce within an animal cell. Coccidian parasites infect the intestinal tracts of animals, and are the largest group of apicomplexan protozoa.
Myxobolus cerebralis is a myxosporean parasite of salmonids that causes whirling disease in farmed salmon and trout and also in wild fish populations. It was first described in rainbow trout in Germany a century ago, but its range has spread and it has appeared in most of Europe, the United States, South Africa, Canada and other countries. In the 1980s, M. cerebralis was found to require a tubificid oligochaete to complete its life cycle. The parasite infects its hosts with its cells after piercing them with polar filaments ejected from nematocyst-like capsules.
Trematodes are parasitic flatworms of the class Trematoda, specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secretory and absorptive functions.
Tetracapsuloides bryosalmonae is a myxozoan parasite of salmonid fish. It is the only species currently recognized in the monotypic genus Tetracapsuloides. It is the cause of proliferative kidney disease (PKD), one of the most serious parasitic diseases of salmonid populations in Europe and North America that can result in losses of up to 90% in infected populations.
Buddenbrockia plumatellae is a worm-like parasite of bryozoans whose taxonomic placement long puzzled biologists. It is now classified as one of only three myxozoans in the Malacosporea subclass and its only family, Saccosporidae, on the basis of both genetic and ultrastructural studies. It was the first multicellular myxozoan identified and its vermiform shape initially gave strong support to the theory that the enigmatic group belongs among the Bilateria. Five years later, this was refuted by a study of fifty genes from this same "worm", which had rarely even been seen since its discovery in 1851. These 50 phylogenetic markers reveal that Buddenbrockia is closely related to jellyfish and sea anemones, typical members of the animalian phylum Cnidaria. Because of the highly divergent nuclear protein sequences of Buddenbrockia, relative to those of the other animals compared in this study, only the use of a sophisticated tree-building approach allowed for recovery of its cnidarian evolutionary affinities. One of the researchers talked about the problems encountered studying its morphology: “It has no mouth, no gut, no brain and no nerve cord. It doesn’t have a left or right side or a top or bottom – we can’t even tell which end is the front!” As the myxozoans are now demonstrably non-bilaterian in origin, he concluded that “the worm-like body shape evolved at least twice from two completely different kinds of animal.”
Leucocytozoon is a genus of parasitic alveolates belonging to the phylum Apicomplexa.
Like humans and other animals, fish suffer from diseases and parasites. Fish defences against disease are specific and non-specific. Non-specific defences include skin and scales, as well as the mucus layer secreted by the epidermis that traps microorganisms and inhibits their growth. If pathogens breach these defences, fish can develop inflammatory responses that increase the flow of blood to infected areas and deliver white blood cells that attempt to destroy the pathogens.
Syndinium is a cosmopolitan genus of parasitic dinoflagellates that infest and kill marine planktonic species of copepods and radiolarians. Syndinium belongs to order Syndiniales, a candidate for the currently uncultured group I and II marine alveolates. The lifecycle of Syndinium is currently not well understood beyond the parasitic and zoospore stages.
Hematodinium is a genus of dinoflagellates. Species in this genus, such as Hematodinium perezi, the type species, are internal parasites of the hemolymph of crustaceans such as the Atlantic blue crab and Norway lobster. Species in the genus are economically damaging to commercial crab fisheries, including causing bitter crab disease in the large Tanner or snow crab fisheries of the Bering Sea.
Cyclospora is a genus of apicomplexan parasites. It includes the species Cyclospora cayetanensis, the causative agent of cyclosporiasis. Members of Cyclospora are characterized as having oocysts with two sporocysts, each containing two sporozoites.
Synchytrium is a large genus of plant pathogens within the phylum Chytridiomycota. Species are commonly known as false rust or wart disease. Approximately 200 species are described, and all are obligate parasites of angiosperms, ferns, or mosses. Early species were mistakenly classified among the higher fungi because of their superficial similarity to the rust fungi. Anton de Bary and Mikhail S. Woronin recognized the true nature of these fungi and established the genus to accommodate Synchytrium taraxaci, which grows on dandelions, and S. succisae, which grows on Succisa pratensis. Synchytrium taraxaci is the type of the genus. The genus has been divided into 6 subgenera based on differences in life cycles.
Chilomastix is a genus of pyriform excavates within the family Retortamonadidae All species within this genus are flagellated, structured with three flagella pointing anteriorly and a fourth contained within the feeding groove. Chilomastix also lacks Golgi apparatus and mitochondria but does possess a single nucleus. The genus parasitizes a wide range of vertebrate hosts, but is known to be typically non-pathogenic, and is therefore classified as harmless. The life cycle of Chilomastix lacks an intermediate host or vector. Chilomastix has a resistant cyst stage responsible for transmission and a trophozoite stage, which is recognized as the feeding stage. Chilomastix mesnili is one of the more studied species in this genus due to the fact it is a human parasite. Therefore, much of the information on this genus is based on what is known about this one species.
Polypodium is a genus of cnidarians that parasitizes in the eggs of sturgeon and similar fishes. It is one of the few metazoans (animals) that live inside the cells of other animals.
Contracaecum is genus of parasitic nematodes from the family Anisakidae. These nematodes are parasites of warm-blooded, fish eating animals, i.e. mammals and birds, as sexually mature adults. The eggs and the successive stages of their larvae use invertebrates and increasing size classes of fishes as intermediate hosts. It is the only genus in the family Anisakidae which can infect terrestrial, marine and freshwater animals.
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