206 The Sarcodina 



Feeding is predominantly holozoic, and food includes other Protozoa, 

 algae, and occasionally rotifers or other small invertebrates. After cap- 

 ture of such organisms, axial filaments may disappear in the immediate 

 region and a layer of cytoplasm surrounds the prey (Fig. 5. 3, E). Occa- 

 sionally, captured microorganisms pass immediately into the deeper cy- 

 toplasm where digestion is completed (Fig. 5. 3, A-D). In addition to 

 axopodia, lobopodia are sometimes formed (158) and the ingestion of 

 food by means of gullet-like "food cups" also may occur (Fig. 5. 3, G). 

 A protozoan version of the hunting pack has been described in Raphi- 

 docystis infestans (158). A ciliate, for example, may be attacked by a 

 number of these Heliozoida, which adhere to the prey and may fuse to 

 form a continuous layer of protoplasm enclosing the captured food (Fig. 

 5. 3, H, I). A simple life-cycle — including an active stage and a cyst — has 

 been reported in a number of Heliozoida. Cysts with a siliceous ectocyst 

 have been described in certain species (108). An alternation of genera- 

 tions, in one of which flagellate gametes are produced, has been reported 

 in Wagnerella borealis (163), although this account has not been con- 

 firmed. The formation of a flagellate daughter organism (Fig. 5. 7, D, 

 L), which leaves the parental test, has been described in Monomastigo- 

 cystis (129) and Hedriocystis (54). 



The work of Belar and his predecessors has established the occurrence 

 of pedogamy in certain Heliozoida, or at least the occurrence of syngamy 

 following a gametic meiosis (Chapter II). The zygote so produced nor- 

 mally undergoes encystment. 



Subdivision of the Heliozoida has been based largely upon the presence 

 or absence of skeletal elements and their structure. On such a basis, the 

 group may be divided into three suborders: (1) Actinophrydina, the 

 naked types; (2) Acanthocystidina, with a gelatinous capsule in which 

 separate skeletal elements are usually embedded; and (3) Desmothora- 

 cina, with a continuous test containing a number of pores. 



Suborder 1. Actinophrydina. There is no capsule or test enclosing the 

 outer zone of vacuolated cytoplasm. Since there is no central granule, the 

 axopodia may end near the nuclear membrane (Fig. 5. 4, E) in uninu- 

 cleate species, or near a nucleus or inner margin of the vacuolated layer 

 in inultinucleate types. Just beneath the vacuolated zone of Actinosphae- 

 rium eichorni, there is a finely granular layer (Fig. 5. 4, B) which may 

 serve as a support for the bases of the axopodia (83, 108). Inside the 

 granular layer lies the finely vacuolated endoplasm. The boundary be- 

 tween endoplasm and ectoplasm is not so sharply defined in the smaller 

 Actinophrydina. 



The suborder includes the following genera: Actinophrys Ehrenberg (5, 6, 83. 108; 

 Fig. 5. 4, C-F), uninucleate fresh-water types; Actinosphaerium Stein (83, 108; Fig. 5. 

 4, A, B), multinucleate fresh-water types; Cawptonema Schaudinn (133), multinucleate 

 marine forms. Actinosphaerium eichornii, which often measures more than 300^^ and 



