Phylum Protoplasta [ 197 



Legion Actipyea or Acantharia, sublegions Acanthometra and Acanthophracta, 

 and orders Actinellida, Acanthonida, Sphaerophracta, and Prunophracta 

 Haeckel Radiolarien II Teil (1887). 

 Order Actipylida Delage and Herouard Traite Zool. 1 : 204 ( 1896) . 

 Suborder Acantharia Minchin Protozoa 256 (1912). 

 Order Acanthometrida Poche in Arch. Prot. 30: 212 (1913). 

 Order Actipylea Calkins Biol. Prot. 345 (1926). 

 Suborder Actipylea Kudo Handb. Protozool. 216 (1931). 

 Suborder Actipylina Hall Protozoology 216 (1953). 



In this group the central capsule membrane has many punctures arranged in 

 clusters. The skeleton includes radiating spicules; in some examples these extend 

 through the cell from side to side, passing through the central capsule; in the majority, 

 their proximal ends meet in the center of the central capsule. In the latter forms, 

 the number of radiating spicules is twenty, and they are arranged according to a pat- 

 tern discovered by Johannes Miiller and called Miiller's law; they form five parallel 

 whorls of four. Usually they bear tangential branches of definite, often highly elab- 

 orate, patterns: these may form a globular frame, or two or more concentric frames. 



Haeckel, Hertwig, and Brandt found the spicules not to consist of silica. They are 

 soluble in acids and alkalis, and were reported to be destroyed by heat. They were 

 supposed, accordingly, to consist of some organic substance; Haeckel named it acan- 

 thin. Schewiakoff found them resistant to heat, and Biitschli (1906) analyzed them 

 and found them to consist of strontium sulfate. This surprising fact has recently been 

 confirmed by Odum (1951). 



The cytoplasm at each point where a spicule passes through the surface is attached 

 to the spicule by a whorl of minute fibers called myophrisks. The myophrisks are 

 believed to be contractile, and to have the function of changing the volume, and 

 hence the density, of the cells, enabling them to sink or float. 



Young cells contain a single nucleus, eccentric in the central capsule; older ones 

 have several to many nuclei. 



Haeckel Hsted twenty families in his legion Acantharia. Other authors recognize 

 about a half dozen, including the following. 



Family Litholophida Haeckel (1882). Family Astrolophida Haeckel (1887). Spi- 

 cules numerous, radiating, not arranged according to Miiller's law. Litholophus, As- 

 trolophus, Actinelius, etc. 



Family Chiastolida Haeckel (1887). Spicules ten to twenty, extending clear 

 through the body. Chiastolus, Acanthochiasma. 



Family Acanthometrida Haeckel (1862). Acanthometren J. MuUer (1859). Fam- 

 ily Acanthonida Haeckel ( 1882). With twenty spicules arranged according to Miiller's 

 law; they may be branched, but do not form a continuous network. In most examples, 

 as Acanthometron, Xiphacantha, etc., they are equal; in others, as Amphilonche, two 

 of the spicules of the equatorial whorl are much longer than the others. 



Family Sphaerocapsida Haeckel (1882). Family Dorataspida Haeckel I.e. Order 

 Sphaerophracta Haeckel (1887). Like the foregoing, but the branches of the radiat- 

 ing spicules forming a globular network, or two or more concentric networks. Dora- 

 taspis, Sphaerocapsa, Lychnaspis. 



Family Diploconida Haeckel (1862). Order Prunophracta Haeckel (1887). Again 

 hke the foregoing, but with the eight spicules of the two polar whorls either extended 

 or abbreviated. Diploconus, Hexaconus. 



