The order Collodaria, the first order of Radiolaria, comprises all those Spumellaria in which the skeleton is either entirely wanting, or represented by numerous single, solid, siliceous needles or spicules, loosely scattered in the calymma around the central capsule. Never in this order is there any trace of the latticed or fenestrated shell, which characterises the second order, Sphærellaria. The skeleton exhibits no trace of phylogenetic connection in the two orders.
In my monograph (1862) two families appertaining to this order are described, the Collida (p. [244]) and the Sphærozoida (p. [521]). Both families contain forms with and without a skeleton. Of the solitary or monozous Collida the Thalassicollida are devoid of a skeleton, whilst the Thalassosphærida are provided with a skeleton. Of the social or polyzous Sphærozoida the Collozoida are without a skeleton, the Rhaphidozoida provided with one. As the special form in both skeletophorous subfamilies is exactly the same, I prefer now to associate them in the suborder Beloidea, and to oppose them to the other two skeletonless subfamilies, which are united under the name of Colloidea.
Synopsis of the four Families of Collodaria.
Suborder I. COLLOIDEA. Skeleton entirely wanting. |  | Solitary cells, living as isolated individuals (Colloidea monozoa), | 1. Thalassicollida. |
| Associated cells, living in colonies or cœnobia (Colloidea polyzoa), | 2. Collozoida. | ||
Suborder II. BELOIDEA. Skeleton composed of numerous needles or spicula, scattered in the calymma. | | Solitary cells, living as isolated individuals (Beloidea monozoa), | 3. Thalassosphærida. |
| Associated cells, living in colonies or cœnobia (Beloidea polyzoa), | 4. Sphærozoida. |
| Skeleton entirely wanting. | ||||
| Solitary cells, living as isolated individuals (Colloidea monozoa), | ||||
| 1. Thalassicollida. | ||||
| Associated cells, living in colonies or cœnobia (Colloidea polyzoa), | ||||
| 2. Collozoida. | ||||
| Suborder II. BELOIDEA. Skeleton composed of numerous needles or spicula, scattered in the calymma. | ||||
| Solitary cells, living as isolated individuals (Beloidea monozoa), | ||||
| 3. Thalassosphærida. | ||||
| Associated cells, living in colonies or cœnobia (Beloidea polyzoa), | ||||
| 4. Sphærozoida. | ||||
Suborder I. COLLOIDEA, Haeckel.
Definition.—Spumellaria without skeleton.
The suborder Colloidea comprises all those Spumellaria in which no skeleton is developed. The whole body is therefore soft—a true malacoma—and is composed only of two essential parts, the central capsule and the enveloping extracapsulum. The suborder contains only two different families, the solitary Thalassicollida (or Colloidea monozoa) and the associated Collozoida (or Colloidea polyzoa). Both families are very nearly allied, and differ only in one single essential character: the solitary life of the former, the social union of the latter. It seems to be merely in consequence of this difference that the cleavage of the nucleus commonly takes place very late in the former, very early in the latter.
Therefore the full-grown Thalassicollida (till immediately before propagation) commonly exhibit one single nucleus in the centre of the capsule, whilst in the Collozoida the capsule is distended by numerous small nuclei. In these latter the centre of the capsule usually contains one large oil-globule, whilst in the former oil-globules are either wanting, or scattered in large numbers in the endoplasm, or disposed in one layer on the inside of the capsule membrane.