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. ); whereas the second subfamily, Tessaraspida, possesses on each radial spine four crossed apophyses (opposite in pairs), like its ancestral group, the Stauracanthida (p. ). 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. , 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. , , ).

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. , figs. 1-4), partly Peltophracta (the Ceriaspida, Pl. ). On the other hand the Tessaraspida (with four crossed apophyses on each spine) are also partly Cladophracta (the Stauraspida, Pl. , figs. 5-8), partly Peltophracta (the Lychnaspida, Pls. -). 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.

Already the central bases, by which the twenty spines are united in the centre of the sphere, exhibit certain differences in the five zones. Commonly these bases are small pyramids, all meeting with their apex in the centre, and the triangular faces of the neighbouring pyramids are supported one upon another. The four equatorial pyramids are commonly six-sided, the other sixteen five-sided; but sometimes there are eight six-sided and twelve five-sided basal pyramids; two opposite polar spines on each pole having a six-sided base (like the four equatorial), the other two polar spines on each pole having a five-sided base (like the eight tropical). Rarely the central bases are perfectly grown together, forming a single spherical central piece of acanthin.

The three different fundamental forms of radial spines, which are found in all Acantharia, the cylindrical, the two-edged, and the four-edged (spines with circular, with elliptical, and with square transverse section respectively) occur also in the different groups of Dorataspida; but commonly the two-edged or compressed form is prevalent in the Diporaspida, the four-edged or quadrangular form in the Tessaraspida. In the majority of species the spines are thickened in the shell-face, where the apophyses arise, and thinner towards the two ends. Usually the outer or distal part of the spine (outside the shell) is longer than the inner or proximal part (inside the shell). The distal apex is commonly simple, conical or pyramidal, rarely bifid or truncate. The edges of the spines are commonly smooth, rarely denticulate or serrate.

The apophyses, or the lateral transverse processes of the radial spines, in the Dorataspida assume the greatest variety and complexity in form, size, mode of ramification, and in composition of the shell. An expert and practised observer may determine easily the range of each spine, whether it be an equatorial (c), or a tropical (b, d), or a polar spine (a, e, Pls. -). The two opposite apophyses of the Diporaspida, as well as the four crossed apophyses of the Tessaraspida, lie constantly in certain meridian planes of the spine, which have a legitimate signification for each of the five zones. The comparative morphology of this regular disposition of the apophyses and the regular meeting of their branches is of the greatest interest, and necessary for the complete understanding of the complicated structure of these wonderful shells.

The pores or meshes of the spherical shell, offering the most varied forms, may generally be divided into two different groups, into sutural and parmal meshes. The sutural pores are bordered by the meeting branches of the apophyses of two, three, or four neighbouring spines, and therefore also by the sutures in which they meet. The parmal pores on the other hand are bordered only by the united branches of the apophyses of a single spine and pierce the shield or lattice-plate formed by them. Therefore the shell-meshes of the Cladophracta are all sutural pores (Pl. , figs. 1-8; rarely and only in a part of the spines parmal pores also: Zonaspis, Dodecaspis); whereas the shell-meshes of the Peltophracta, piercing the shields or lattice-plates of all twenty spines, are always partly sutural, partly parmal pores (Pls. , , ). The parmal pores again may be divided into two different groups—aspinal and coronal pores. Aspinal pores ("ad spinam") are those which lie immediately on the sides of the radial spine and are bordered by the primary branches of its apophyses; therefore constantly only two in the Diporaspida, four in the Tessaraspida. Coronal pores on the contrary are those which lie in the periphery of the lattice-plates, surrounding in a circle or crown the aspinal pores and not touching the spine itself. In Dorataspis, Ceriaspis, Tessaraspis, Lychnaspis, &c., all parmal meshes are only aspinal pores (Pl. , figs. 2-5; Pl. ); whilst in Coscinaspis, Acontaspis, Icosaspis, Hylaspis, &c., one part of the parmal pores is aspinal, one part coronal (Pl. ). The number, form, and size of the coronal pores is very variable and often very large (sometimes more than a hundred in one plate).

The Cladophracta exhibit a comparatively simple shell-formation; either all twenty spines or at least a part of them not forming lattice-plates. The most primitive form among these is Phractaspis (Pl. , figs. 1, 2). The forty apophyses of its twenty spines are simply forked, and their eighty fork-branches united by forty sutures, enclosing twenty-two sutural meshes: two square polar meshes (between the four polar spines on the poles of the spineless axis, a a a a and e e e e); eight triangular circumpolar meshes (each between two polar and one tropical spine, a b a and e d e); eight quadrangular tropical meshes (each between one polar, one equatorial, and two tropical spines, a b c b and e d c d); and four rhomboidal equatorial meshes (between two tropical and two equatorial spines, c b c d). If the fork-branches be again forked (Phractaspidium, Pl. , fig. 3), the number of the sutures and sutural meshes is doubled, and the same is the case in Stauraspis, the most simple form of the Tessaraspida.

A peculiar small group, and an interesting transition for the Cladophracta to the Peltophracta, is presented by the Zonaspida among the Tessaraspida (Zonaspis and Dodecaspis). Here only one part of the radial spines bears lattice-plates, the other part not. In Zonaspis the four equatorial spines bear lattice-plates, the sixteen other only free branches of the apophyses. In Dodecaspis twelve spines are provided with lattice-plates (four equatorial and eight polar spines), whilst the eight other (tropical) spines are devoid of them.

The Peltophracta exhibit a great variety in the form and composition of their twenty lattice-plates or fenestrated shields. In the most simple case (a part of Dorataspis and Diporaspis) the shell is composed of four (equatorial) hexagonal plates, and sixteen pentagonal plates (four tropical and four polar); in this case the four polar plates meet on each pole in one common point. More commonly, however, the shell seems to be composed of eight hexagonal plates (four equatorial and the four polar spines of the hydrotomical plane) and twelve pentagonal plates (eight tropical and the four polar spines of the geotomical plane); in this case only two (hexagonal) polar plates meet on each pole in a suture which separates the two other (pentagonal) polar plates (Pl. , fig. 4). In the majority of the Dorataspida the composition of the shell is much more complicated and often very difficult to understand. Often the surface of the plates is covered with a network of elevated crests, by which concave blind dimples are separated (Ceriaspis, Hystrichaspis, Pl. ); and sometimes these dimples become pierced by coronal pores (Pl. , fig. 11, &c.).

Peculiar by-spines or "accessory spines" cover the outer surface of the shell in a great part of Dorataspida, and commonly these most characteristic by-spines are not placed radially, but parallel to the radial spine, from the lattice-plate of which they arise (Pl. , figs. 1, 5; Pl. , figs. 4-8; Monogr. d. Radiol., 1862, Taf. xxi. figs. 8, 9). They are commonly placed perpendicular to the sutural condyles, or the branch-ends of the apophyses; so that close to each suture arises a pair of divergent by-spines, belonging to the meeting apophyses of the two neighbouring spines, which meet in the suture (Pl. , fig. 4). Rarely these thin, bristle-shaped by-spines are quite simple and straight, commonly they undulate or are zigzag and often armed with recurved hooks. Sometimes they are also forked or arborescent (Pl. , fig. 7).

The Central Capsule of the Dorataspida is constantly spherical and about one-third smaller than the enclosing shell, from which it is separated by the spherical calymma. The membrane of the central capsule is commonly rather thin, and pierced by the twenty radial spines, meeting in the centre of the capsule. Between these lie innumerable small pores for the radiating pseudopodia; however, in many cases (and perhaps constantly) these pores exhibit a certain regular disposition. In many species the central capsule encloses Xanthellæ or symbiotic yellow unicellular Algæ. The nucleus becomes cleft very early in the majority of Dorataspida.

Synopsis of the Genera of Dorataspida.

II. Subfamily Diporaspida.

Each radial spine with two opposite primary apophyses; therefore the whole shell with forty primary apophyses.

I. Tribe Phractaspida. Twenty radial spines without lattice-plates; no normal pores. No by-spines, 349. Phractaspis.

With by-spines, 350. Pleuraspis.

II. Tribe Ceriaspida. Twenty radial spines all with lattice-plates produced by union of the branched apophyses of each plate. Forty parmal pores (two in each plate)—no coronal pores in the plates. Plates not dimpled, without network of crests. No by-spines, 351. Dorataspis.

With by-spines, 352. Diporaspis.

No by-spines, but free apophyses, 353. Orophaspis.

Plates dimpled, with a network of crests. No by-spines, 354. Ceriaspis.

With by-spines, 355. Hystrichaspis.

Eighty to two hundred or more parmal pores (in each plate two aspinal and two to ten or more coronal pores). No by-spines, 356. Coscinaspis.

With by-spines, 357. Acontaspis.

II. Subfamily Tessaraspida.

Each radial spine with four crossed primary apophyses; therefore the whole shell with eighty primary apophyses.

III. Tribe Stauraspida. Twenty radial spines all or partly without lattice-plates. All twenty spines without lattice-plates. No by-spines, 358. Stauraspis.

With by-spines, 359. Echinaspis.

Four plates with, sixteen without, lattice-plates. With by-spines, 360. Zonaspis.

Twelve plates with, eight without, lattice-plates. With by-spines, 361. Dodecaspis.

IV. Tribe Lychnaspida. Twenty radial spines all with lattice-plates (produced by union of the branched apophyses of each plate). Eighty parmal pores (four on each plate)—no coronal pores in the plates. No by-spines, 362. Tessaraspis.

With by-spines, 363. Lychnaspis.

One hundred and sixty to three hundred or more parmal pores (in each plate four aspinal and four to twelve or more coronal pores). No by-spines, 364. Icosaspis.

With by-spines, 365. Hylaspis.

I. Subfamily Diporaspida. Each radial spine with two opposite primary apophyses; therefore the whole shell with forty primary apophyses.

I. Tribe Phractaspida. Twenty radial spines without lattice-plates; no normal pores.

No by-spines,

349. Phractaspis.

With by-spines,

350. Pleuraspis.

II. Tribe Ceriaspida. Twenty radial spines all with lattice-plates produced by union of the branched apophyses of each plate.

Forty parmal pores (two in each plate)—no coronal pores in the plates.

Plates not dimpled, without network of crests.

No by-spines,

351. Dorataspis.

With by-spines,

352. Diporaspis.

No by-spines, but free apophyses,

353. Orophaspis.

Plates dimpled, with a network of crests.

No by-spines,

354. Ceriaspis.

With by-spines,

355. Hystrichaspis.

Eighty to two hundred or more parmal pores (in each plate two aspinal and two to ten or more coronal pores).

No by-spines,

356. Coscinaspis.

With by-spines,

357. Acontaspis.

II. Subfamily Tessaraspida. Each radial spine with four crossed primary apophyses; therefore the whole shell with eighty primary apophyses.

III. Tribe Stauraspida. Twenty radial spines all or partly without lattice-plates.

All twenty spines without lattice-plates.

No by-spines,

358. Stauraspis.

With by-spines,

359. Echinaspis.

Four plates with, sixteen without, lattice-plates.

With by-spines,

360. Zonaspis.

Twelve plates with, eight without, lattice-plates.

With by-spines,

361. Dodecaspis.

IV. Tribe Lychnaspida Twenty radial spines all with lattice-plates (produced by union of the branched apophyses of each plate).

Eighty parmal pores (four on each plate)—no coronal pores in the plates.

No by-spines,

362. Tessaraspis.

With by-spines,

363. Lychnaspis.

One hundred and sixty to three hundred or more parmal pores (in each plate four aspinal and four to twelve or more coronal pores).

No by-spines,

364. Icosaspis.

With by-spines,

365. Hylaspis.