The Calymma or the jelly-veil, including the central capsule, in the Acantharia is more or less voluminous, and commonly envelops the skeleton perfectly. In its surface is sometimes developed a peculiar network of "supporting fibres." A very peculiar product are the remarkable "Myophrisca" of the Acanthometra, which are wanting in the Acanthophracta; they were first detected by Johannes Müller, and figured as "Cilien-Kränze," afterwards explained by Hertwig as "contractile Fäden," similar to muscular fibrillæ (compare below).
The Matrix, placed between the calymma and central capsule, in the majority of the Acantharia is a rather thin layer of granular exoplasm.
The Pseudopodia arising from it are not so numerous as in the Spumellaria, and not so equally disposed over the whole surface. Also their tendency to ramify, anastomose, and form networks seems to be much less developed. Commonly they are simple or little ramified. In many cases (and perhaps everywhere) there may be distinguished two different kinds of pseudopodia:—(1) Axopodia, or permanent pseudopodia (with axial filaments?), piercing the wall of the central capsule, and arising from the central mass of endoplasm; and (2) Collopodia, or variable pseudopodia (without axial filaments), arising outside the capsule from the matrix of extracapsular sarcode or from the exoplasm on the surface of the calymma. These and other differentiations seem to indicate that the pseudopodia in the Acantharia are more highly developed than in the Spumellaria, and justify the denomination of the former as "Actipylea."
Synopsis of the Orders and Suborders of Acantharia.
II. ACANTHOMETRA. Skeleton composed only of acanthinic radial spines not forming a complete lattice-shell. |  | Radial spines in variable and indefinite number, disposed irregularly, | 1. Actinelida. |
| Radial spines constantly twenty, disposed regularly after the Müllerian law of Icosacantha, | 2. Acanthonida. | ||
II. ACANTHOPHRACTA. Skeleton composed of twenty acanthinic radial spines (disposed after the Müllerian law) and of a spherical or variously shaped complete lattice-shell. | | Radial spines all twenty of equal size; shell and central capsule spherical, | 3. Sphærophracta. |
| Radial spines of different sizes; shell and central capsule ellipsoidal, discoidal, or heteromorphous, | 4. Prunophracta. |
| I. ACANTHOMETRA. Skeleton composed only of acanthinic radial spines not forming a complete lattice-shell. | ||||
| Radial spines in variable and indefinite number, disposed irregularly, | ||||
| 1. Actinelida. | ||||
| Radial spines constantly twenty, disposed regularly after the Müllerian law of Icosacantha, | ||||
| 2. Acanthonida. | ||||
| II. ACANTHOPHRACTA. Skeleton composed of twenty acanthinic radial spines (disposed after the Müllerian law) and of a spherical or variously shaped complete lattice-shell. | ||||
| Radial spines all twenty of equal size; shell and central capsule spherical, | ||||
| 3. Sphærophracta. | ||||
| Radial spines of different sizes; shell and central capsule ellipsoidal, discoidal, or heteromorphous, | ||||
| 4. Prunophracta. | ||||
Order III. ACANTHOMETRA, Johannes Müller, 1855.
Acanthometra, J. Müller, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin.
Acanthometrida, Haeckel, 1862, Monogr. d. Radiol., p. 371.