D. Phaeodaria (Cannopylaea, Haeck.; Tripylaea, Hertw.).—Central capsule spheroidal, of two layers, in its outer layer an operculum, with radiate ribs and a single aperture, beyond which protrudes the outer layer; osculum basal, a dependent tube (proboscis); accessory oscula, when present, simpler, usually two placed symmetrically about the apical pole; skeleton siliceous, with a combination of organic matter, often of hollow spicules; nucleus sphaeroidal, eccentric; extracapsular protoplasm containing an accumulation of dusky pigment granules ("phaeodium").
Fig. 23.—Actinomma asteracanthion. A, the shell with portions of the two outer spheres broken away; B, section showing the relations of the skeleton to the animal, cent.caps, Central capsule; ex.caps.pr, extra-capsular protoplasm: nu, nucleus; sk.1, outer, sk.2, middle, sk.3, inner sphere of skeleton. (From Parker and Haswell, after Haeckel and Hertwig.)
A. Spumellaria.
Sublegion (1). Collodaria.[[86]]—Skeleton absent or of detached spicules; colonial or simple.
Order i. Colloidea.—Skeleton absent. (Families 1, 2.) Thalassicolla Huxl.; Thalassophysa Haeck.; Collozoum Haeck.; Collosphaera J. Müll.; Actissa Haeck.
Order ii. Beloidea.—Skeleton spicular. (Families 3, 4.)
Sublegion (2). Sphaerellaria.—Skeleton continuous, latticed or spongy, reticulate.
Order iii. Sphaeroidea.—Skeleton of one or several concentric spherical shells; sometimes colonial. (Families 5-10.) Haliomma Ehrb.; Actinomma Haeck. (Fig. 23).
Order iv. Prunoidea.—Skeleton a prolate sphaeroid or cylinder, sometimes constricted towards the middle, single or concentric. (Families 11-17.)