Myxosporidia

Myxosporea
Kudoa septempunctata - spores
Scientific classification
Kingdom:	Animalia
Phylum:	Cnidaria
(unranked):	Myxozoa
Class:	Myxosporea Buetchli 1881

The Myxosporea are 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 (generally an annelid) 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 recently they were treated as belonging to different classes within the Myxozoa.

In the vertebrate host, organisms belonging to the Myxosporea are characterised by spores composed of several cells, contained within between 1 and 7 shell "valves". These cells include 1 or two amoeboid infective germ cells, and 2 to 7 -like polar capsules. During some stages of the life cycle, the germ cells are completely contained within cells of the host.

The myxosporean species are typically defined by the size and shape of the spores released by vertebrate hosts. For instance, the genus Ceratomyxa is a common parasite of the gallbladder of many fish species; they have "boomerang-like" spores with two polar capsules resembling eyes in the middle of the spore. Most species within the myxosporea are sized between 10 μm and 20 μm, however Myxidium giganticum is up to 98 μm long.

The spore shell consists of shell "valves", which are joined together along "suture lines". Some species contain polysaccharide reserves in the form of β-glycogen particles, which are concentrated in a central "iodinophillous vacuole".

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Wikipedia