Thalassosphærida, Monogr. d. Radiol., p. 255.
Definition.—Beloidea solitaria.
The family Thalassosphærida comprises all solitary Spumellaria with an imperfect skeleton, composed of numerous solid needles or spicula, scattered around the central capsule in the calymma. The structure of the unicellular soft body is quite the same as in the Thalassicollida; it differs from these only in the possession of the extracapsular skeleton. All needles of this skeleton are solid siliceous spicula, never hollow, as in the similar Cannorrhaphida among the Phæodaria. In the special structure and form of the skeleton the Thalassosphærida agree perfectly with the well-known, colony-building Sphærozoida; they differ from these only by their hermit-like life and by some peculiarities derived from this solitary development.
The oldest known form of this family is probably the first Radiolarian, observed in the living state, described in 1834 by Meyen as Physematium atlanticum (see p. [35]). A second form was figured in my Monograph (1862) as Thalassosphæra bifurca (p. 260, Taf. xii. fig. 1). A third form was there described under the name Thalassosphæra morum; this remarkable form was first observed by Johannes Müller, and figured under the name Thalassicolla morum (1858, Abhandl., p. 28, Taf. vii. figs. 1, 2). The same form was afterwards observed living by myself in the Mediterranean, as well as in the Atlantic, and in great numbers by the late Sir Wyville Thomson in the Pacific. The latter gave a good figure of it with some valuable remarks in his excellent work, The Atlantic (1877, vol. i. p. 233, fig. 51). He called this peculiar Rhizopod Calcaromma calcarea, on account of the very peculiar calcareous bodies "looking in outline like the rowels of spurs," which are accumulated in great quantity around the central capsule, in the calymma. Further investigations have convinced me that these peculiar stellate bodies of carbonate of lime, for which we propose the name "Calcastrella," are not parts of the skeleton produced by the Radiolarian, but foreign bodies picked up by its extracapsular sarcode (in the same way as the Coccoliths are picked up by Thalassicolla sanguinolenta = Myxobrachia!). These Calcastrella occur also in the calymma of some Discoidea and other Radiolaria; they are either unicellular calcareous Algæ, or foreign bodies of other origin. The Collodarium, however, described as Thalassicolla morum and Calcaromma calcarea, seems to be a simple Actissa, which has picked up a number of Calcastrella.
The Challenger collection has yielded a number of other true Thalassosphærida, which partly agree with Thalassosphæra in the simple structure of the unicellular body (resembling Actissa), and partly differ from it in the development of alveoles, either within or without the central capsule (similar to Thalassolampe and Thalassicolla). The solid siliceous spicula, which occur in great numbers scattered in the calymma, agree perfectly in form with the spicula of the colony-building Sphærozoida. A characteristic difference between the social and the solitary Beloidea seems to be determined by the cleavage of the nucleus, which takes place in the latter very late, in the former very early. Therefore in the large central capsule of the mature solitary Thalassosphærida, we commonly find one large nucleus in the centre, and a number of oil-globules around it in the endosarc, or disposed in one layer on the inside of the capsule-membrane (Pl. [2], figs. 2, 5); whereas in the much smaller associated capsules of the Sphærozoida one large oil-globule is placed commonly in the centre, and a great number of small nuclei scattered in the endoplasm (compare above, p. [24]).
Synopsis of the Genera of Thalassosphærida.
| A. Alveoles neither within nor without the central capsule. |  | Spicula simple, | 07. Thalassosphæra. |
| Spicula branched, | 08. Thalassoxanthium. | ||
| B. Numerous large alveoles within the central capsule (not in the calymma). |  | Spicula simple, | 09. Physematium. |
| C. Numerous large alveoles within the calymma (not in the central capsule). | | Spicula simple, | 10. Thalassoplancta. |
| Spicula branched, | 11. Lampoxanthium. |
| A. Alveoles neither within nor without the central capsule. | ||||
| Spicula simple, | ||||
| 7. Thalassosphæra. | ||||
| Spicula branched, | ||||
| 8. Thalassoxanthium. | ||||
| B. Numerous large alveoles within the central capsule (not in the calymma). | ||||
| Spicula simple, | ||||
| 9. Physematium. | ||||
| C. Numerous large alveoles within the calymma (not in the central capsule). | ||||
| Spicula simple, | ||||
| 10. Thalassoplancta. | ||||
| Spicula branched, | ||||
| 11. Lampoxanthium. | ||||
Genus 7. Thalassosphæra,[[14]] Haeckel, 1862, Monogr. d. Radiol., p. 259.
Definition.—Thalassosphærida without alveoles, with simple, unbranched, needle-shaped spicula in the calymma.