INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

PROTISTS - PROTISTA

PROTOZOA

ALVEOLATES

PHYLUM APICOMPLEXA

CLASS GREGARINES (GREGARINEA)

A distinct group of parasites localized in the body cavity and the intestinal lumen of invertebrates, primarily Arthropods. About 500 species are known. Many of them are characterized by an intracellular parasitic phase. The size of gregarines ranges from 16 µm to 16 mm.

Morphology. The gregarine Cell typically consists of three parts: the anterior epimerite, the middle protomerite, and the posterior deutomerite, which are separated from one another by a layer of transparent ectoplasm (Fig. 45). The single Nucleus is located in the deutomerite. The epimerite serves for attachment to the host's intestinal wall, which often bears hooks or complexly shaped outgrowths.

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Fig. 45. Gregarines (from Polyansky): a - general view of Corycella armata from the intestine of a whirligig beetle;

b - its epimerite embedded in an intestinal epithelial cell; c - an individual that has shed its epimerite; d - a syzygy of Clepsidrina blattarum from the cockroach intestine; 1 - epimerite; 2 - protomerite; 3 - deutomerite; 4 — nucleus

A young individual initially parasitizes inside The Cell, feeding via a cytostome located on the epimerite. During growth, the parasite

moves from the cell into the intestinal lumen, remaining attached by the epimerite to the cell remnants. In some species inhabiting the host's body cavity, the epimerite and occasionally the protomerite are absent (Fig. 45, d). Gregarines exhibit a peculiar smooth (gliding) movement, The Mechanism of which remains poorly understood.

Life cycle. In most gregarines, schizogony is absent, involving only the alternation of a sexual process with sporogony (Fig. 46). The infective stage is the sporozoite contained within an oocyst. Inside the host Organism, they shed their membranes and briefly parasitize within the intestinal epithelial Cells. Subsequently, the parasites rupture the host cell and develop into mature gamonts, remaining attached to the cell remnants by means of the epimerite. Gamonts pair up to form a syzygy and, without fusing, become enclosed within a common envelope known as a gamontocyst. Each gamont then undergoes multiple successive mitotic divisions to form Gametes. Within the syzygy, gametes originating from different gamonts fuse in pairs.

Fig. 46. Life Cycle of the gregarine Stylocephalus longicollis (from Polyansky):

1 - sporozoite; 2 - gamont; 3 - syzygy; 4 - gamontocyst; 5, 6 - gamete formation;

7 - formed gametes; 8 - gamete copulation; 9 - oocyst; 10-14 - development of sporozoites within the oocyst (sporogony);

15 - release of sporozoites from the oocyst

The Sexual process in gregarines takes the form of isogamy or heterogamy, and the gametes are flagellated. Zygotes within the gamontocyst develop a thick, dense envelope, transforming into oocysts. Within each oocyst, meiotic division occurs first, followed by mitotic division, resulting in The formation of several sporozoites. Through the host's excrement or secretions, the oocysts enter the external environment and are ingested by a new host. Upon release of the sporozoites, the cycle repeats. Thus, The life cycle of gregarines features zygotic chromosomal reduction.

Clepsidrina blattarum parasitizes the digestive tract of cockroaches (Fig. 45). Recently, attempts have been made to utilize certain species of the order Neogregarinida in biological control Methods against insect pests.