Heliozoa.

Heliozoa. or 'sun-animalcules,' a class of Protozoa of the Rhizopod type—i.e. provided with protruding processes of living matter. These processes are unlike those of the Amœbæ (q.v.) in being slender and radiant, unlike those of Foraminifera (q.v.) in being stable and rarely interlaced. The unit-mass or cell of which the Heliozoon consists is globular and stable, with one nucleus or with many, and usually with vacuoles both contractile and non-contractile. There is generally a 'skeleton,' gelatinous or siliceous, and in the latter case either continuous or composed of loose spicules. Multiplication is effected by division of the cell into two, or by budding, or by that internal fission known as spore-formation. In some cases the spores or young Heliozoa are flagellate, and thus very unlike the comparatively slow and passive adults. In a few instances Heliozoa have been seen united in colonies. The majority live in fresh water, but some are marine. Common examples are Actinospherium, Actinophrys, Raphidiophrys, and Clathulina. See PROTOZOA; Bütschli's Protozoa in Broun's Thierreich.