38 



PROTOZOA RHIZOPODA 



CLASS 



Haeckel divides the Radiolaria into four sub-orders, as follows : 



A. Acantharia. Capsule-membrane uniformly perforated ; skeleton com- 

 posed of acanthinic spicules. Unknown in fossil state. 



B. SpumeUaria. Capsule -membrane single, pores distributed all over; 

 skeleton silicious, spherical, or discoidal, sometimes wanting (Fig. 48). 



C. Nasselaria. Capsule-membrane single, perforated only about the oral 

 pole ; skeleton silicious, helmet- or cap-shaped, conformation of poles dissimilar 

 (Figs. 49, 50). 



D. Phaeodaria. Capsule-membrane double, perforated by one main opening 

 prolonged into a tubulus, and by a few smaller accessory openings. A dark 



FIG. 46. 



Silurian and Devonian Radiolarians : A, Cenosphaera macropora, Riist. Ordovician ; Cabrieres, Languedoc. 

 L, Staurolonche micropora, Riist. Ordovician ; Cabrieres. C, Caryosphaera Groddecki, Riist. Upper Devonian ; 

 Schiibenliolz, near Elbingerode, Harz Mountains. D, Lithocampe Tschernytscheicii, Riist. Devonian ; Ural. 

 Magnified 100120 diameters (after Riist). 



pigment body (phaeodium) constantly present in extra-capsular sarcode. Skeleton 

 commonly consisting of hollow silicious spicules disposed in flask-shaped or 

 variously shaped frameworks. Unknown in fossil state. 



Radiolarians are exclusively marine organisms, and are found at all bathy- 

 metric zones. They occur in vast numbers, especially in tropical seas, 



FIG. 47. 



Carboniferous, Jurassic, and Cretaceous Radiolarians : A, Stauracontium inaequale, Riist. Carboniferous ; 

 Sicily. B, Trochodiscus Nicholsoni, Riist. Carboniferous ; Harz. C, Xiphodictya acuta, Riist. In coprolite 

 from Lias ; Ilsede, Hanover. D, Hymeniastrum rolundum, Riist. In coprolite from Cretaceous ; Zilli,[Saxony. 



swimming on the surface, as well as at medium and even abysmal depths ; 

 particularly between 2000 4000 fathoms in depth, extensive deposits of 

 " Radiolarian mud " have been found, the composition of which is largely silica 

 with a small percentage of carbonate of lime. 



The diversity of form exhibited by Radiolarians is most astonishing, and 

 the identification of their microscopic silicious skeletons is impossible without 



