The Sarcodina 215 



though the literature contains repeated descriptions of flagellate stages 

 (flagellispores) — supposedly gametes. However, syngamy has not been ob- 

 served, and Chatton (23) concluded that some of these supposed flagellate 

 stages are probably parasites. This conclusion certainly seems justified for 

 "flagellispores" which are similar to dinoflagellates. However, some of 

 these flagellates (80) obviously are not dinoflagellates (Fig. 5. 10) and 

 they show a marked resemblance to flagellate gametes of Foraminiferida 

 (Fig. 5. 42). 



Although the Radiolarida are not swimmers, at least some of them 

 apparently can rise or sink in response to changing environmental con- 

 ditions. A collapse of vacuoles in the calymma increases the specific grav- 

 ity of the organism and thus induces sinking; regeneration of the vacuoles 

 reverses this effect. Such a mechanism enables species living near the 



Fig. 5. 10. "Flagellispores" (gametes?) of Radiolarida: A, B. Acantho- 

 metra pellucida, dividing gametocyte showing paradesmose (A) and biflag- 

 ellate gamete (B); x4000 (after Le Calvez). C. Xiphicantha alata, x4000 

 (after Le Calvez). D, E. Coelodendrum ramosissimum, living (D) and 

 stained (E); x2550 (after Le Calvez). 



surface to sink when disturbed by rough wave action or when the tem- 

 perature becomes unfavorable. 



The majority of species probably live within the upper 1,500 feet, al- 

 though a few forms have been dredged from depths of 2-3 miles. Within 

 this vertical range, the fauna varies to a considerable extent with depth. 

 The majority of the Peripylina are found within the upper 200 feet, while 

 the Actipylina are most abundant below 150-200 feet. The Tripylina are 

 to be found mainly within a range of 1,200 to 3,500 feet. The group as a 

 whole is widely distributed over the oceans, although specific distribution 

 varies considerably. Some species show essentially universal distribution 

 while others may be limited to tropical or to polar waters. The greatest 

 variety of species occurs within the equatorial zone. Radiolarian skeletons, 

 sinking to the bottom, make up deposits of radiolarian ooze, and many 

 fossil types are known. 



