{ 10}_Synopsis of the four Families of Collodaria._
Suborder I. { Solitary cells, living COLLOIDEA. { as isolated individuals { (_Colloidea monozoa_), 1. THALASSICOLLIDA. Skeleton entirely { wanting. { Associated cells, living { in colonies or coenobia { (_Colloidea polyzoa_), 2. COLLOZOIDA.
Suborder II. { Solitary cells, living as BELOIDEA. { isolated individuals { (_Beloidea monozoa_), 3. THALASSOSPHÆRIDA. Skeleton composed { of numerous { Associated cells, living in needles or { colonies or coenobia spicula, scattered { (_Beloidea polyzoa_), 4. SPHÆROZOIDA. in the calymma. {
_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.
In the solitary Thalassicollida each capsule is enclosed in its own peculiar spherical calymma, whilst in the associated Collozoida all capsules of the colony are united in one common, very voluminous calymma.
Family I. #THALASSICOLLIDA#, Haeckel, 1862.
_Thalassicollida_, Haeckel, 1862, Monogr. d. Radiol., p. 246. _Thalassicollida_, Haeckel, 1881, Prodromus, p. 469.
The family Thalassicollida comprises all solitary SPUMELLARIA without a skeleton. The oldest and best known form of this family is the genus _Thalassicolla_, as restricted by { 11}Johannes Müller.[4] The most common representative of it, the cosmopolitan _Thalassicolla nucleata_, was first described by Huxley in 1851. But as early as 1834 another large Radiolarian, appertaining either to this or to a nearly allied family, had been described by Meyen as _Physematium atlanticum_. A third genus was detected by me in 1859 at Messina and figured under the name _Thalassolampe margarodes_.[5] A very accurate histological description of these forms was given in 1876 by Richard Hertwig.[6] The same author figured in his Organismus in 1879 a very interesting simpler form under the name _Thalassolampe primordialis_ (Taf. iii. fig. 5). Some similar forms had already been observed by me, and are here united with it to form the first genus _Actissa_.[7]