SPECIAL MORPHOLOGY AND TAXONOMY OF SARCODINA 319 



Sub-class I. HELIOZOA, Haeckel. 



Heliozoa are t^'picalh' fresh-water forms although several species 

 of marine forms are known. They are homaxial and floating in 

 habitat for the most part but stalked and attached forms are occa- 

 sionally met with {WagnereUa horealis, Clathndina elegans, etc.). 

 They are either naked (Aphrothoraca) or covered by a gelatinous 

 mantle without spicules (Chlamydophora), or with spicules (Chal- 

 arothoraca) or provided with a definite latticed shell (Desmo- 

 thoraca) . 



Pseudopodia are typically radial with central axial filaments which 

 penetrate the endoplasm. Here they end, or rather begin, either 

 in a nucleus (Actinrrphrys, CaniiAonema nidans, etc.), or in a central 

 kinetic granule called the Centralkorn by Grenacher (1869) (Acan- 

 thocystis, Syhwrastrum, WagnereUa, etc.). In such cases the nucleus 

 is excentric. In Camptoneina nutans a single axial filament arises 

 from each of the many nuclei and there are as many pseudopodia 

 as there are nuclei (Fig. 148). In WagnereUa horealis the nucleus 

 is in the basal plate, while the central granule, wdtli radiating axial 

 filaments, is in an enlargement at the other end of the stalk. 



The body protoplasm is alveolar and characterized by two zones 

 which in some cases are clearly differentiated as ectoplasm and 

 endoplasm {e. g., Actinosphceriuin) but in most genera they are 

 rather indefinite. The ectoplasm is made up of relatively large 

 pseudo-alveoli in Adinophrys and ActinosphcBrium and is very dif- 

 ferent from the dense ectoplasm of Amoeba. The endoplasm is 

 more finely granular and contains one or more nuclei (up to two 

 hundred or more in ActinosphoBrium). Symbiotic forms are not 

 infrequent in the endoplasm and are regarded as aflagellate forms of 

 Phytomastigoda. 



Contractile vacuoles are present in fresh-water species but are 

 generally absent in salt-water forms. They are developed in the 

 cortex and resemble slightly enlarged ectoplasmic vesicles bursting 

 to the outside. 



Nutrition is holozoic, minute lobose pseudopodia being protruded 

 which capture and draw in minute organisms as food. In Canipto- 

 nema, however, the axopodia are able to bend and several of them 

 may be directed toward the capture of living prey (Fig. 14.3). 



Reproduction is ordinarily by binary fission or by budding, while 

 incomplete division frequently leads to colony formation as in 

 Haphidiophrys. Sexual processes have been described for only a 

 few forms (Adinophrys, Aciinosphceriuni) (see Chapter XI) while 

 flagellated swarm spores which may turn out to be gametes, are 

 known for Acanthocystis, Clathndina and WagnereUa. 



If doubtful forms resembling Heliozoa, but without axial filaments 

 {e. g., Nnclearia, VampyreUa, etc.) are transferred to the Sarcodina 



