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

SUBKINGDOM PROTOZOA (PROTOZOA)

PHYLUM SARCOMASTIGOPHORA (SARCOMASTIGOPHORA)

SUBPHYLUM Sarcodina (Sarcodina)

SUPERCLASS ACTINOPODA (ACTINOPODA)

CLASS HELIOZOA (HELIOZOEA)

Most heliozoans inhabit freshwater bodies, although marine and parasitic species also exist. A total of about 100 species are known.

Heliozoans generally lack a mineral Skeleton, although both freshwater (Clathrulina elegans) and marine species with a siliceous lattice-like spherical skeleton are known. Unlike radiolarians, heliozoans lack a central capsule, and their ectoplasm and endoplasm are distinctly differentiated (Fig. 26). The ectoplasm of planktonic forms contains numerous vacuoles designed to reduce specific gravity. The endoplasm contains either a single Nucleus (genus Actinophrys) or multiple nuclei (genus Actinosphaerium); contractile vacuoles are localized in the ectoplasm. The prey of heliozoans consists of Protozoans as well as small Multicellular Organisms (such as rotifers) that adhere to axonemes, becoming immobilized, possibly due to the secretion of toxic substances by the axonemes. Digestive vacuoles form on The Cell surface and subsequently sink into the endoplasm, where Digestion takes place. Heliozoans reproduce by division. Daughter individuals of shelled species abandon their parent skeleton, and each forms a new one. Some species produce flagellated spores; a sexual process also occurs. Symbiotic plant flagellates or unicellular Algae frequently inhabit the Cytoplasm.

Class="center">

Fig. 26. Heliozoans — Actinophrys sol (a); Actinosphaerium eichhorni, general view (b) and body region (c), Clathrulina elegans (d):

1 — ectoplasm; 2 — axoneme; 3 — endoplasm; 4 — contractile vacuole; 5 — nucleus; 6 — digestive vacuole; 7 — skeleton; 8 — stalk