Family XL. Dorataspida, Haeckel (Pls. 134-138).
Dorataspida, Haeckel, 1862, Monogr. d. Radiol., p. 412.
Definition.—Acantharia with simple spherical lattice-shell, composed of the branched apophyses of twenty equal radial spines meeting in its centre and disposed according to the Müllerian law of Icosacantha. Central capsule spherical, enclosed in the fenestrated shell.
The family Dorataspida is the most important family of the Acanthophracta, or of those Acantharia in which the radial spines are connected by a complete extracapsular lattice-shell. The Dorataspida represent probably the ancestral stock of this whole order, with the exception of the Sphærocapsida. The four following families of the order may be easily derived from the Dorataspida. The number of genera (seventeen) and of species (one hundred and eight) is in this family greater than in the other five families together. When I constituted that family in my Monograph 1862, it comprised only one genus, Dorataspis, with seven species. The nearly allied genus Haliommatidium (Phatnaspis) belongs to the Belonaspida.
The Dorataspida differ from the other Acanthophracta in the simple spherical lattice-shell, which is composed of the meeting apophyses of the twenty radial spines. In three other families of the suborder the shell is not spherical, but ellipsoidal (Belonaspida), discoidal (Hexalaspida), or diploconical (Diploconida). In the Phractopeltida the spherical shell is double, composed of two concentric lattice-spheres. In the Sphærocapsida the simple spherical shell is not composed of the apophyses of the spines, but of innumerable small plates.
The family Dorataspida may be divided into two very different subfamilies, which are probably derived, independently of one another, from two different subfamilies of the Astrolonchida. The first subfamily, Diporaspida, exhibits on each radial spine two opposite apophyses, like its ancestral group, the Phractacanthida (p. [753]); whereas the second subfamily, Tessaraspida, possesses on each radial spine four crossed apophyses (opposite in pairs), like its ancestral group, the Stauracanthida (p. [758]). Therefore the composition of the spherical shell, produced by the meeting branches of the tangential apophyses, is essentially different in the two subfamilies: in the Diporaspida each radial spine is surrounded by two opposite primary aspinal meshes, in the Tessaraspida by four crossed primary aspinal meshes.
Another principle of division may be established for the whole family by the different mode of composition of the shell, and regarding this important difference we may distinguish also two different subfamilies as Cladophracta and Peltophracta. In the first and simpler subfamily, the Cladophracta, the shell is composed totally (or sometimes partially) of the meeting branches of the apophyses of the neighbouring spines; but in each single spine (or in the most part of them) the branches of the apophyses are not united, and form no lattice-plate (Pl. [137], figs. 1 to 8). Whereas in the Peltophracta the shell is composed constantly of twenty perforated plates, as in each single spine the branches of its apophyses are united and form a fenestrated shield with two or four (and sometimes numerous) pores (Pls. [135], [136], [138]).
In the Diporaspida as well as in the Tessaraspida we find numerous representatives of the two groups of the Cladophracta and of the Peltophracta; therefore the whole family of Dorataspida may be divided into four different tribes. The Diporaspida (with two opposite apophyses on each spine) are partly Cladophracta (the Phractaspida, Pl. [137], figs. 1-4), partly Peltophracta (the Ceriaspida, Pl. [138]). On the other hand the Tessaraspida (with four crossed apophyses on each spine) are also partly Cladophracta (the Stauraspida, Pl. [137], figs. 5-8), partly Peltophracta (the Lychnaspida, Pls. [135]-[136]). The differences and relations of these tribes are placed synoptically in the following table:—
| Synopsis of the four tribes of Dorataspida. | A. Diporaspida. Two opposite apophyses on each radial spine. Two primary aspinal meshes. | B. Tessaraspida. Four crossed apophyses on each radial spine. Four primary spinal meshes. |
|---|---|---|
| a. Cladophracta All twenty spines (or a part of them) without lattice-plates. | 1. Tribe Phractaspida. | 3. Tribe Stauraspida. |
| b. Peltophracta All twenty spines with lattice-plates. | 2. Tribe Ceriaspida. | 4. Tribe Lychnaspida. |
All Dorataspida are true Icosacantha, and the twenty spines, composing the spherical shell, are equally developed, regularly disposed according to the Müllerian law, and of equal size; also the distance of their plates from the common centre is equal. Nevertheless they are never of perfectly the same form; in consequence of their peculiar disposition in five zones (each with four spines) certain slight differences are effected, so that with accurate knowledge of the peculiar shell-composition it is generally not difficult to distinguish the spines of the equatorial, the two tropical, and the two polar zones.