''Monocystis'' (Gr., ''monos'', single + ''kystisis'', bladder) is a genus (the type of the family

Monocystidae The Monocystidae are a family of parasitic alveolates in the phylum Apicomplexa. Taxonomy There are five subfamilies in this family: Monocystinae, Oligochaetocystinae, Rhynchocystinae, Stomatophorinae and Zygocystinae. History This fami ...

) of acephaline gregarines (subclass

Gregarinasina The gregarines are a group of Apicomplexan alveolates, classified as the Gregarinasina or Gregarinia. The large (roughly half a millimeter) parasites inhabit the intestines of many invertebrates. They are not found in any vertebrates. Gregarines ...

) not having the protoplasm divided into segments by septa and including internal parasites of

invertebrates Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum ...

(as ''M. agilis'' of the reproductive system of

earthworms An earthworm is a soil-dwelling terrestrial animal, terrestrial invertebrate that belongs to the phylum Annelida. The term is the common name for the largest members of the class (biology), class (or subclass (biology), subclass, depending on ...

Habit and habitat

''Monocystis'' lives as an intracellular

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

in its young stage, when it lives in the bundle of developing

sperm Sperm (: sperm or sperms) is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm ...

. It becomes extracellular in its mature stage, living in the contents of seminal vesicles of earthworms. Its infection is so widespread that practically all mature earthworms are found parasitized by this parasite.

Structure

The mature adult of ''Monocystis'' is a feeding stage called a

trophozoite A trophozoite (G. ''trope'', nourishment + ''zoon'', animal) is the activated, feeding stage in the life cycle of certain protozoa such as malaria-causing ''Plasmodium falciparum'' and those of the ''Giardia'' group. The complementary form of the t ...

. The young trophozoite lives in the sperm

morula In embryology, cleavage is the division of cells in the early development of the embryo, following fertilization. The zygotes of many species undergo rapid cell cycles with no significant overall growth, producing a cluster of cells the same siz ...

(group of developing sperm) of the host; it feeds and grows at the expense of the

protoplasm Protoplasm (; ) is the part of a cell that is surrounded by a plasma membrane. It is a mixture of small molecules such as ions, monosaccharides, amino acids, and macromolecules such as proteins, polysaccharides, lipids, etc. In some definitions ...

of the developing sperm until all the protoplasm is exhausted and it is surrounded by the tails of the dead sperm cells. In this stage, it is sometimes mistaken for a

cilia The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

ted organism, but the sperm tails soon detach from its body and the trophozoite becomes free. The adult is an elongated, spindle-shaped, flattened, wormlike creature. Its body is covered by a thick, smooth, and permeable pellicle. The cytoplasm is well differentiated into ectoplasm and

endoplasm Endoplasm, also known as entoplasm, generally refers to the inner (often granulated), dense part of a cell's cytoplasm. This is opposed to the ectoplasm (cell biology), ectoplasm which is the outer (non-granulated) layer of the cytoplasm, which ...

, the latter containing a large vesicular nucleus. Its nutrition is sporozoic. There are no locomotory organs, but it shows wriggling and gliding movements.

References

{{Taxonbar, from=Q18606206 Conoidasida Apicomplexa genera