Ascetosporea

The Haplosporidia are a group of single-celled organisms that live as parasites inside various of aquatic animals. They have economic importance as pathogens in mussel cultures. Systematically, they belong to the Rhizaria.

• 4.1 Notes and references

Features

Life cycle

The Haplosporidia have a complex life cycle which is fully understood, however, with any of the species. In the digestive tract of the host slip from the spores small amoeboid cells. These migrate into the connective tissue or epithelium, where they grow into multinucleate plasmodia. The large plasmodia divide irregularly to smaller plasmodia with different number of cores. This division cycle is repeated several times. The resulting plasmodia spread extracellularly from the tissue. At the beginning of sporulation forms around a large, multinucleate plasmodium a cell wall, the plasmodium is to Sporont. Here it is likely to karyogamy and subsequently to meiosis. The remaining stages of the life cycle should all be haploid. The Sporont divides several times later and forms mononuclear sporoblasts.

Another school of thought says that combine two haploid to a diploid zygote sporoblasts, and the diploid stage is maintained throughout the remainder of the life cycle. Which of the two assumptions is correct or whether both occur is not clear.

From the sporoblasts two halves form: the seedless half, Episporoplasma, envelops the nucleated half, sporoplasm and separates from him by cell division. This results in a nucleated cell in the interior of the vacuole of a coreless cell. The Episporoplasma now forms the spore wall and then degenerates. The spore wall includes many species-specific ornamentation, and at one end a flap with which the spore opens later.

The presence of intermediate hosts is believed, but has not been demonstrated.

Organelles

To specific organelles Haplosporidia have Haplosporosomen. These are located in the cytoplasm of sporonts and sporoblasts. These are spherical, the electron density of a plasma membrane vesicle is surrounded with a diameter of 70 to 250 nm to contain membranous structures and glycoproteins. Their function is unknown.

The Spherulosomen be interpreted as descendants of the Golgi apparatus. You are in the front end of the spores and swell during germination of the spore.

The other organelles have no peculiarities. The mitochondria are a thing of the tubules - vesicular type. The core shell of the nucleus remains intact during mitosis, the spindle apparatus remains inside the cell nucleus. A portion of the spindle apparatus is maintained even during interphase as so-called core rod.

Occurrence

The Haplosporidia occur world-wide. They live as parasites in the tissues, especially of molluscs, but also of echinoderms, crustaceans, and tunicates Vielborstern. Haplosporidia may result in oyster cultures in significant economic losses.

System

The Haplosporidia today consist of about 30 species, the total number of species is estimated to be several hundred.

The Haplosporidia following genera are counted:

• Urosporidium
• Haplosporidium
• Minchinia
• Bonamia

The genus Claustrosporidium is partly made ​​to the Haplosporidia, partly made ​​on the basis of ultrastructural features independently a par with the Haplosporidia. However, molecular genetic studies of the genus are missing.

Documents

• Klaus Hausmann, Norbert Hülsmann, Renate Radek: Protistology, 3rd edition, Schweizerbart, 2003, pp. 124-127, ISBN 3-510-65208-8