The Apicomplexa are organisms of a large phylum of mainly parasitic alveolates. Most possess a unique form of organelle structure that comprises a type of (non-photosynthetic) plastid called an apicoplast—with an apical complex membrane. The organelle's apical shape is an adaptation that the apicomplexan applies in penetrating a host cell.
Myxozoa is a subphylum of aquatic cnidarian animals – all obligate parasites. It contains the smallest animals ever known to have lived. Over 2,180 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.
In biology, a biological life cycle is a series of stages of the life of an organism, that begins as a zygote, often in an egg, and concludes as an adult that reproduces, producing an offspring in the form of a new zygote which then itself goes through the same series of stages, the process repeating in a cyclic fashion.
The Rhizaria are a diverse and species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many foraminifera and radiolaria have a symbiotic relationship with unicellular algae. A multicellular form, Guttulinopsis vulgaris, a cellular slime mold, has been described. This group was used by Cavalier-Smith in 2002, although the term "Rhizaria" had been long used for clades within the currently recognized taxon. Being described mainly from rDNA sequences, they vary considerably in form, having no clear morphological distinctive characters (synapomorphies), but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. In the absence of an apomorphy, the group is ill-defined, and its composition has been very fluid. Some Rhizaria possess mineral exoskeletons, which are in different clades within Rhizaria made out of opal, celestite, or calcite. Certain species can attain sizes of more than a centimeter with some species being able to form cylindrical colonies approximately 1 cm in diameter and greater than 1 m in length. They feed by capturing and engulfing prey with the extensions of their pseudopodia; forms that are symbiotic with unicellular algae contribute significantly to the total primary production of the ocean.
Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or protists, but are now known to be fungi, or a sister group to fungi. These fungal microbes are obligate eukaryotic parasites that use a unique mechanism to infect host cells. They have recently been discovered in a 2017 Cornell study to infect Coleoptera on a large scale. So far, about 1500 of the probably more than one million species are named. Microsporidia are restricted to animal hosts, and all major groups of animals host microsporidia. Most infect insects, but they are also responsible for common diseases of crustaceans and fish. The named species of microsporidia usually infect one host species or a group of closely related taxa. Approximately 10 percent of the species are parasites of vertebrates —several species, most of which are opportunistic, can infect humans, in whom they can cause microsporidiosis.
Perkinsus marinus is a species of alveolate belonging to the phylum Perkinsozoa. It is similar to a dinoflagellate. It is known as a prevalent pathogen of oysters, causing massive mortality in oyster populations. The disease it causes is known as dermo or perkinsosis, and is characterized by the degradation of oyster tissues. The genome of this species has been sequenced.
Perkinsus is a genus of alveolates in the phylum Perkinsozoa. The genus was erected in 1978 to better treat its type species, Perkinsus marinus, known formerly as Dermocystidium marinum. These are parasitic protozoans that infect molluscs, at least some of which cause disease and mass mortality. P. marinus is the most notorious, causing the disease perkinsosis, or dermo, in wild and farmed oysters.
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.
The Ascetosporea are a group of eukaryotes that are parasites of animals, especially marine invertebrates. The two groups, the haplosporids and paramyxids, are not particularly similar morphologically, but consistently group together on molecular trees, which place them near the base of the Cercozoa. Both produce spores without the complex structures found in similar groups.
Ostrea is a genus of edible oysters, marine bivalve mollusks in the family Ostreidae, the oysters.
Enterocytozoon bieneusi is a species of the order Chytridiopsida which infects the intestinal epithelial cells. It is an obligate intracellular parasite.
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.
Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is typified by a cellular variety with a distinct morphology and biochemistry.
Bonamia ostreae is a parasitic rhizarian that can cause lethal infections in shellfish, particularly the European flat oyster, Ostrea edulis. Infection in oysters rarely results in clinical signs of disease and often the only indication of the infection is increased mortality. The Australian flat oyster, Ostrea angasi, has been infected with two similar Bonamia parasites, Bonamia exitiosa and B. roughleyi.
Urastoma cyprinae is a turbellarian that infects the gills of numerous species. It has been reported as free-living organism in marine mud and on algae. Urastoma cyprinae is reported as an opportunistic mantle inhabitant on the gills of various bivalve species, including the clams Tridacna maxima and Tridacna gigas, and the mussels Mytilus edulis and Mytilus galloprovincialis. They are also found throughout the gill surface of C. virginica and is attracted by mucus that coats the gills of oysters. However, the nature of the host-parasite relationship remains unknown.
Hemolivia is a genus of the phylum Apicomplexia.
Nematopsis (Nee-mah-top-cis) is a genus gregarine Apicomplexan of the family Porosporidae. It is an aquatic parasite of crustaceans with a molluscan intermediate host. Nematopsis has been distinguished from the similar genus Porospora by its resistant and encapsulated oocyst. Little molecular biology has been performed on the members of the Nemaptosis and species are described based on molluscan and crustacean hosts as well as oocyst structure. A total of 38 species have been described and are found all over the world.
Ichthyodinium is a monotypic genus of dinoflagellates in the family Dinophysaceae. Ichthyodinium chabelardi (/ɪkθioʊˈdɪniəm/) is currently the sole described species of the genus.
Mytilicola orentalis is an intestinal copepod parasite of bivalves with a direct life cycle. It is native to the waters around Japan and was first described in the Japanese Sea and was introduced to Europe in the 1960s and 70's with oyster imports. Since then it has also been observed in the Wadden and the Baltic Sea. It has a wide range of host species in both its native range and in Europe.
Txikispora is a genus of parasitic protists made up solely of the species Txikispora philomaios. It is the only genus in the family Txikisporidae, which is a member of the class Filasterea and is closely related to Ministeriidae. The lineage was first described in 2022 based on specimens identified from the United Kingdom. The species represents a previously undiscovered type of life that diverged extremely early from animals and fungi. It parasitizes amphipods in the genera Echinogammarus and Orchestia and most frequently infects their hemolymph and hemocytes.
