THE HELIOZOA 33 



by encystment within any definite period, and Hertwig has obtained 

 cysts from individuals in which it had certainly not occurred for 

 several weeks. 



CLASS HELIOZOA, HAECKEL. 

 ORDER 1. Aphrothoraca, Hertwig. 



Heliozoa usually devoid of a skeletal or gelatinous envelope. A 

 membranous envelope, sometimes with siliceous spicules, is only developed 

 during encystment. 



Genera Actinophrys, Ehrb. ca. 50 ft. Cosmopolitan in fresh water 

 and probably cosmopolitan in the sea (Fig. 2). Camptonema, Schaud. 

 Numerous small contractile vacuoles and about 50 nuclei. 120-180 ft. 

 Marine, Norway. Actinosphaerium, Stein (Fig. 1). Two or more large con- 

 tractile vacuoles, numerous nuclei. 1 mm. Cosmopolitan in fresh water. 

 Gymnosphaera, Sassaki. Numerous nuclei. Very numerous and very long 

 pseudopodia. 140 /x. Pseudopodia up to 800 /A in length. Actinolophus, 

 F. E. Schultze. Body usually pear-sheaped. One nucleus. Pseudopodia 

 long and thin. Sometimes (always t) with a thin gelatinous membrane 

 perforated by the pseudopodia. Attached to a foreign object by a- long 

 hollow stalk. Body 30 JJL in diameter. Stalk 100 ft long by 3-4 p. in 

 diameter. Marine. North Sea. The genus Actinosphaeridium, Zacharias, 

 freshwater, Germany, is closely related to Actinolophus. The genera 

 Zooteirea, Wright, an oval form with a contractile stalk, from the 

 Firth of Forth, Estrella, Frenzel, and Phythelius, Frenzel, are imper- 

 fectly known. Phythelius is probably an Alga. Nuclearia (see p. 8), 

 Cienkowski, differs from the other Heliozoa in having an amoeboid 

 body and pseudopodia without any definite axis. It is sometimes 

 regarded as a Proteomyxan. Myxodiscus crystalligerus is a form that is 

 doubtfully placed among the Heliozoa. It was found by Prowazek in a 

 sea-water aquarium. The genus Archerina, Lankester, which has been 

 regarded by some authors as a Proteomyxan and by others as a Heliozoon, 

 is now placed by Lankester (12) among the Algae. It is the same genus as 

 Golenkinia (Chodat), belonging to the Pleurococcaceae, the naked proto- 

 plasm surrounding the green organism in many instances observed and 

 figured by Lankester being that of a Vampyrella-like or amoeboid 

 organism symbiotic with or merely crawling on the alga. 



ORDER 2. Chlamydophora, Archer. 



Heliozoa with a soft mucilaginous envelope, but without any solid 

 skeletal elements. 



Astrodisculus, Greeff (Fig. 2 (8)). Body spherical. Pseudopodia very long 

 and delicate. Several species recently described by Penard. Freshwater. 

 20-40 ft. The genus Heliophrys, Greeff, is evidently closely related to 

 Astrodisculus, but has also been placed with Heterophrys (see West [21]). 

 The form described by Greeff as Chondropus viridis is regarded by Penard 

 as a peculiar species of Vampyrella, 



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