Chapter 16 

 Class 2 Sarcodina Butschli 



THE members of this class do not possess any definite pellicle 

 and, therefore, are capable of forming pseudopodia (p. 40). 

 The term 'amoeboid' is often used to describe their appearance. 

 The pseudopodia serve for both locomotion and food-capturing. 

 The peripheral portion of the body shows no structural dif- 

 ferentiation in Amoebina, Proteomyxa, and Mycetozoa. Internal 

 and external skeletal structures are variously developed in other 

 orders. Thus, in Testacea and Foraminifera, there is a well- 

 developed test or shell that usually has an aperature, through 

 which the pseudopodia are extruded; in Heliozoa and Radiolaria, 

 skeletons of various forms and materials are developed. 



The cytoplasm is, as a rule, differentiated into the ectoplasm 

 and the endoplasm, but this differentiation is not constant. In 

 Radiolaria, there is a perforated membranous 'central capsule' 

 which marks the border line between the two cytoplasmic layers. 

 The endoplasm contains the nuclei, food vacuoles, various 

 granules, and contractile vacuoles. The majority of Sarcodina 

 are uninucleate, but numerous species of Foraminifera and 

 Mycetozoa are multinucleate. In the family Paramoebidae, there 

 occurs a peculiar 'secondary nucleus.' 



The Sarcodina are typically holozic, but in a few cases holo- 

 phytic. Their food organisms are Protozoa, small Metazoa and 

 Protophyta, which present themselves conspicuously in the 

 cytoplasm. One or more contractile vacuoles are invariably pres- 

 ent in forms inhabiting the fresh water, but absent in parasitic 

 forms or in those which live in the salt water. 



Asexual reproduction is usually by binary (or rarely multiple) 

 fission, budding, or plasmotomy. Definite proof of sexual re- 

 production has been given in a comparatively small number of 

 species. Encystment is common in the majority of Sarcodina, but 

 is unknown in a few species. The life-cycle has been worked out 

 in some forms and seems to vary among different groups. The 

 young stages are either amoeboid or flagellate, and on this 

 account, it is sometimes very difficult to distinguish the Sarcodina 

 and the Mastigophora. In some forms the mature trophic stage 



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