216 The Sarcodina 



Taxonomy.^ The Radiolarida are subdivided, on the basis of skeletal 

 structure and the distribution of pores in the capsule, into four suborders: 

 (1) Actipylina ("Acantharia"), with a skeleton composed basically of 

 radial spines which penetrate the central capsule to converge in the mid- 

 dle of the body; (2) Peripylina ("Spumellaria"), often with no skeleton 

 or one limited to disconnected extracapsular rods and less commonly with 

 a perforated shell; the spherical central capsule shows uniformly dis- 

 tributed pores; (3) Monopylina ("Nasselaria"), with a thick central cap- 

 sule in which the pores are limited to one zone, or "porous plate" (Fig. 





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Fig. 5. 11. A. Ceiiosphaera tnacroponi Riist, from Ordovician (Lower 

 Silurian) deposits; x]20 approx. (after R.). B. Staurolonche micropora Riist 

 (Ordovician), xl20 approx. (after R.). C. Branched central capsule of Cyto- 

 r'ndus spinosus, x5 (after Schroder). D. ThalassicoUa nucleata, from living; 

 central capsule (surroimded by zone of small vacuoles), layer of hyaline 

 cytoplasm, calymma, and axopodia (after Huth). 



5. 12, F); and (4) Tripylina ("Phaeodaria"), in which the central capsule 

 has one major and two accessory openings (Fig. 5. 13, A). 



Suborder 1. Actipylina. The central capsule, sometimes irregular in 

 shape, is rather uniformly perforated, although arrangement of the pores 

 in rows or fields is often recognizable. The skeleton consists mainly of 

 rods which converge inside the central capsule (Fig. 5. 9, A-C) and usually 

 show an arrangement described by Miiller's "law." There are often twenty 



^ More detailed information will be found in such special monographs as the follow- 

 ing: general: Haeckel, E. 1887. Challenger Rep., Zool. 18; Hertwig, R. 1879. Der 

 Organismus der Radiolarien (Jena); Actipylina: Popofsky, A. 1904. Ergebn. Plankton- 

 exped. 3, 1907. Nordisches Plankton 16; Schewiakoff, W. 1926. Fauna Flora G. Neapel 

 37; Peripyliyia: Schroder, O. 1914. Nord. Plankt. 17; Monopylina: Popofsky, A. 1913. 

 Ergebn. Deutsch. Siidpol.-exp. Bd. 14, Zool. 6; Tripylina: Borgert, A. 1903-1911. Ergebn. 

 Planktonexp. 3. 



