Spicula all together simple rods, more or less curved or bent, pointed at both ends, thorny from numerous small spines, placed vertically on the rods.
Dimensions.—Diameter of the central capsule 0.1 to 0.2, length of the spicula 0.07 to 0.15.
Habitat.—Tropical Atlantic, Station 348, surface.
Genus 13. Sphærozoum,[[23]] Meyen, 1834, Nova Acta Acad. Nat. Curios., Bd. xvi., Suppl., p. 287 (p. 163).
Definition.—Sphærozoida with branched or radiate spicula of one kind.
The genus Sphærozoum, with Physematium one of the two oldest Radiolaria, observed in the living state, was founded 1834 by Meyen for one of the social Beloidea, which was probably the common cosmopolitan Sphærozoum punctatum, the true type of this genus. Johannes Müller described a number of species, which were partly skeletonless (Collozoum), partly armed with simple or with compound spicula. The species with simple spicula we refer here to Belonozoum, the species with two or more different kinds of spicula to Rhaphidozoum, while we unite in Sphærozoum all species with one kind of branched or compound spicula. The two following species are incompletely known:—Sphærozoum orientale, Dana, 1863, Ann. and Mag. Nat. Hist., vol. xii. p. 54. Sphærozoum sanderi, Dœnitz, 1871, L. N. [60], p. 71.
Subgenus 1. Sphærozonactis, Haeckel.
Definition.—Spicula radiate, not geminate, consisting of three, four, or more needles or shanks, radiating in different directions from one common central point.
1. Sphærozoum triactinium, n. sp.
Spicula all (or nearly all) triradiate, composed of three (or sometimes in few spicula four) needle-like shanks, diverging from one common point. Shanks straight or somewhat curved, smooth, pointed. Central capsules spherical, with one central oil-vesicle. This species may be regarded as the social form of Thalassoxanthium triactinium.