Synopsis of the Suborders and Families of Acanthometra.
Suborder I. ACTINELIDA. Number of the radial spines variable, either more or less than twenty, commonly disposed irregularly and not according to the Müllerian law. |  | Radial spines very numerous (thirty to a hundred or more), radiating from a common centre within a spherical space, | 1. Astrolophida. |
| Radial spines between ten and twenty, radiating from one common point within a sphere-quadrant, | 2. Litholophida. | ||
| Radial spines of variable number; every two opposite spines grown together in the centre; therefore numerous diametral spines are crossed freely in the centre, | 3. Chiastolida. | ||
Suborder II. ACANTHONIDA. Number of the radial spines constantly twenty, disposed regularly according to the Müllerian law. |  | All twenty radial spines nearly equal, and of the same size and form, | 4. Astrolonchida. |
| Four equatorial spines much larger than (and often also of different form from) the sixteen other spines, | 5. Quadrilonchida. | ||
| Two opposite equatorial spines (or principal spines) much larger than (and often also of different form from) the eighteen other spines, | 6. Amphilonchida. |
| Suborder I. ACTINELIDA. Number of the radial spines variable, either more or less than twenty, commonly disposed irregularly and not according to the Müllerian law. | ||||
| Radial spines very numerous (thirty to a hundred or more), radiating from a common centre within a spherical space, | ||||
| 1. Astrolophida. | ||||
| Radial spines between ten and twenty, radiating from one common point within a sphere-quadrant, | ||||
| 2. Litholophida. | ||||
| Radial spines of variable number; every two opposite spines grown together in the centre; therefore numerous diametral spines are crossed freely in the centre, | ||||
| 3. Chiastolida. | ||||
| Suborder II. ACANTHONIDA. Number of the radial spines constantly twenty, disposed regularly according to the Müllerian law. | ||||
| All twenty radial spines nearly equal, and of the same size and form, | ||||
| 4. Astrolonchida. | ||||
| Four equatorial spines much larger than (and often also of different form from) the sixteen other spines, | ||||
| 5. Quadrilonchida. | ||||
| Two opposite equatorial spines (or principal spines) much larger than (and often also of different form from) the eighteen other spines, | ||||
| 6. Amphilonchida. | ||||
Suborder I. ACTINELIDA, Haeckel, 1882.
Definition.—Acanthometra with a variable number of radial spines, which are commonly irregularly disposed, not according to the Icosacantha.
Family XXXIII. Astrolophida, Haeckel.
Astrolophida, Haeckel, 1881, Prodromus, p. 469.
Definition.—Acantharia with a variable number of simple radial spines, radiating within a spherical space from one common central point which is the centre of the spherical central capsule. No lattice shell.
The family Astrolophida comprises the simplest and the most primitive forms among all Acantharia, and may therefore be regarded as the common ancestral stock of this whole legion or subclass of Radiolaria. The acanthinic skeleton is composed of a variable number of quite simple radial spines, which are united in the centre of the spherical central capsule and radiate, piercing its walls and the surrounding jelly-veil, within a spherical space.