INVERTEBRATE ZOOLOGY IN THREE BOOKS - BOOK 1 - G.Y. Shcherbak - 1995

SUBKINGDOM PROTOZOA (PROTISTA)

PHYLUM SARCOMASTIGOPHORA

SUBPHYLUM Sarcodina

SUPERCLASS RHIZOPODA

CLASS ACRASEA

Previously, representatives of this Class, along with the classes of True Slime Molds and Plasmodiophorids, were considered a distinct division of plants—the Slime Molds (Myxomycota). However, the complete lack of a Cell wall in these three classes, their capacity for amoeboid movement, and phagocytosis indisputably indicate their belonging to the phylum Sarcomastigophora.

Representatives of this class (about 30 species) inhabit decaying plant residues and manure. They appear as uninucleate amoebae that move by means of pseudopodia, feed on organic debris via phagocytosis, and reproduce by fission.

When food supplies are exhausted, the amoebae aggregate, although the Cells do not fuse with one another, forming

a multicellular pseudoplasmodium. In some acraseans, it actively moves using pseudopodia-like outgrowths composed of many cells (the migration stage). After some time, part of the amoebae form a stalk, while the rest crawl up to its apex and form spore heads of various shapes. In some species, the stalk branches whorled, and each branch terminates in a spore HEAD. Inside it, some amoebae encyst, forming so-called spores, which are actually cysts (the dispersal stage). Upon maturation, the spores are released from the ruptured capsule. Under favorable conditions, amoebae emerge from them (Fig. 18). Reproducing rapidly on decaying organic matter, acraseans contribute to its mineralization.

Fig. 18. Life Cycle of Acrasia rosea:

1—spore; 2— amoeboid stage; 3 — pseudoplasmodium; 4 — fruiting body