BRITISH FRESHWATER HELIOZOA. 



SYNOPSIS OF BRITISH SPECIES. 



Nuclei numerous; pseudopodia straight and radiating. 



(1) A. eichhornii. 

 Nuclei few; some of the pseudopodia anastomosing. 



(2) A. arachnoideum. 



1. Actinosphaerium eichhornii (Ehrenb.). 

 (Plate LXV, figs. 1 and 2.) 



? Trichoda sol (part.) 



MULLER Verm. terr. fluv. I, 1773. p. 76. 

 "Der Stern" EICHHORN Zugabe Beytr. Wasserthiere, 1783, p. 15, ff. 



1-7. 

 Actinophrys Eichhornii 



EHRENBERG Ber. Akad. -Berlin, 1840, p. 198. 

 Actinosphaerium Eichhornii 



STEIN Abh. Bohmisch. Ges. (ser. 5) X, Berichte, 1857, p. 41. 



LEIDY Rep. U. S. Geol. Surv. XII, 1879, p. 259, pi. xli. 



PENARD Heliozoaires, 1904, p. 120, ff. 1 and 2. 



Body normally spherical, transparent and nearly 

 colourless ; outer portion or ectoplasm formed of one 

 or two layers of large vacuoles closely pressed together, 

 their walls more or less thinly lined with plasma ; 

 endoplasm containing numerous small vacuoles and 

 separated from the ectoplasm by a narrow zone of 

 denser plasma; nuclei numerous, disseminated in the 

 endoplasm near its periphery, each nucleus containing 

 several nucleoli ; contractile vesicles two or more in 

 number, spherical, large, pulsating slowly; pseudo- 

 podia of moderate length, numerous, not very close 

 together, tapering, containing a firm axis arising from 

 the narrow zone of denser plasma. 



Diameter of mature individuals usually 80 JJL to 300 ^ 

 or 400 /A but may attain 1000 /A or more; young 

 individuals and detached portions are met with of all 

 sizes from 30 p. or less upwards ; the pseudopodia do 

 not exceed the diameter of the body in length ; nuclei 

 usually from 12ju to 20 /x in diameter. 



Habitat. Ponds and lakes. Amongst aquatic 

 vegetation. 



