Family XXXV. Chiastolida, Haeckel
Acanthochiasmida, Haeckel, 1862, Monogr. d. Radiol., p. 402.
Definition.—Acantharia with a variable number of simple radial spines, which are grown together in pairs (two opposite spines of each pair representing together a single diametral spine). Diametral spines crossed loosely in the centre of the spherical or irregular roundish central capsule. No lattice-shell.
The family Chiastolida (or Acanthochiasmida) differs from all other Acantharia in the peculiar mode of the radial spines; these grown together in pairs in the centre of the body, so that every two spines opposite in one axis of the body form together one single diametral spine. All diametral spines are loosely crossed in the middle of the central capsule, or connected by a peculiar screw-like winding, but not united firmly.
I established the family Acanthochiasmida in my Monograph (1862, p. 402) upon the single genus Acanthochiasma (with three species), in which only ten diametral spines are constantly found; I derived these from the twenty radial spines of the common Acanthometra, supposing that every two opposite spines of the latter (lying in one axis) were grown together in the centre, whilst the intimate connection of the twenty radial spines in the common centre was dissolved. This opinion was afterwards confirmed by Richard Hertwig, who observed Acanthochiasma intact in the living state. Although two species of this genus are cosmopolitan and very common, the number of species is very small; I could add to those three older known forms only a single new species.
Another genus of this family, Chiastolus, was observed by me only in a single specimen but it is extremely interesting. It has sixteen diametral spines, disposed quite regularly after the same law of the thirty-two spines of Actinastrum which we described above (compare above, p. ). Therefore we cannot doubt that the former is derived from the latter in the same way, every two opposite radial spines (of one axis) being grown together to form a single diametral spine. As we place Acanthometron (with twenty spines) and Actinastrum (with thirty-two spines) in two different families, it would perhaps be more convenient to separate also Acanthochiasma and Chiastolus as representatives of two different families—Acanthochiasmida (with ten diametral spines) and Chiastolida (with sixteen diametral spines).
As we derive Acanthochiasma from Acanthometron by concrescence in pairs of the twenty radial spines, the Müllerian law of Icosacantha must be employed also to the ten diametral spines of the former, therefore two of them are equatorial, four tropical, and four polar spines. In the same way we may employ the new law of disposition found in the thirty-two radial spines of Actinastrum equally to the sixteen diametral spines of Chiastolus, which we derive from the former, four of them are equatorial, eight tropical, and four polar spines (compare above, p. ).
The Central Capsule of the Chiastolida is spherical, and exhibits in general the same shape as in the Acanthonida, and specially in the Astrolonchida. Of course every diametral spine pierces the capsule twice, at two points diametrically opposed. In some species of Acanthochiasma the central capsule is formed very late, so that it seems often to be absent. A very accurate description of the capsule and its nucleus, as well as of the calymma and the pseudopodia, is given by Richard Hertwig in his Organismus der Radiolarien (1879, pp. 10-18). The pseudopodia are very numerous, and sometimes bear reddish granules.
Synopsis of the Genera of Chiastolida.
I. Subfamily Chiastolidina.
Sixteen diametral spines, derived by concrescence of thirty-two radial spines,
321. Chiastolus.
II. Subfamily Acanthochiasmida.
Ten diametral spines, derived by concrescence of twenty radial spines,
322. Acanthochiasma.
Genus 321. Chiastolus, n. gen.
Definition.—Chiastolida with sixteen diametral spines, derived from thirty-two radial spines opposite and grown together in pairs.
The genus Chiastolus, hitherto known only by a single observed specimen, comprises the Chiastolida with sixteen diametral spines, which are loosely crossed in the centre of the body. Four of these spines are equatorial, four polar, and eight tropical. We derive Chiastolus from Actinastrum by concrescence of every two opposite spines in one axis of the body (compare above, pp. , ).
1. Chiastolus amphicopium, n. sp. (Pl. , figs. 3, 3a, 3b).
Spines in the central part cylindrical, spirally convoluted in a very peculiar manner, broadened towards both ends, strongly compressed, two-edged; the broadest parts are the two truncated distal ends, five to seven times as broad as the thinnest central part, which is placed between two spindle-shaped intumescences. These cochleary central parts of the sixteen spines seem to be resting one upon another. Each spine (composed of two opposite equal radial spines) has nearly the form of a double oar. The single observed specimen (preserved in glycerine) exhibited a most regular disposition of the thirty-two spines (grown together in pairs in the centre). The diameter of the dark non-transparent spherical central capsule equalled one-fifth to one-fourth of the total length of the double spines. When the soft parts of the body were destroyed by sulphuric acid, the sixteen single spines were suddenly dispersed.
Dimensions.—Length of the sixteen double spines 0.5, distal breadth (of the truncated ends) 0.05, central breadth 0.01; diameter of the central capsule 0.12.
Habitat.—South-east Pacific (near Juan Fernandez), Station 297, surface.
Genus 322. Acanthochiasma, Krohn, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 810.
Definition.—Chiastolida with ten diametral spines, derived from twenty radial spines opposite and grown together in pairs.
The genus Acanthochiasma with a small number of common species, comprises the Chiastolida with ten diametral spines, which are loosely crossed in the centre of the body. I could distinguish only four species, two of which are cosmopolitan and very widely distributed. In all four species the diametral spines are quite simple, cylindrical; only in one species distinguished by a spiral winding or torsion in the middle part, where they are crossed one to another. We derive Acanthochiasma from Acanthometron by concrescence of every two spines opposite in one axis of the body.
1. Acanthochiasma krohnii, Haeckel.
Acanthochiasma krohnii, Haeckel, 1862, Monogr. d. Radiol., p.403, Taf. xix. fig. 7.
Acanthochiasma krohnii, R. Hertwig, 1879, Organismus d. Radiol., Taf. ii. fig. 6.
Spines needle-shaped, cylindrical, very thin and long, of equal breadth in their whole length, distinguished by a high degree of elasticity. Central capsule colourless or yellowish-white, transparent. Granules of the sarcode colourless.
Dimensions.—Length of the spines 0.5 to 1.0, breadth 0.001 to 0.002.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, very common.
2. Acanthochiasma rubescens, Krohn.
Acanthochiasma rubescens, Haeckel, 1862, Monogr. d. Radiol., p. 403.
Spines cylindrical, of equal breadth in their whole length, not very elastic, pointed at the two ends. Central capsule intransparent, reddish, with violin-shaped concretions. Granules of the sarcode red coloured.
Dimensions.—Length of the spines 0.2 to 0.6, breadth 0.004 to 0.006.
Habitat.—North Atlantic, Madeira, Krohn; Lanzerote, Haeckel.
3. Acanthochiasma fusiforme, Haeckel.
Acanthochiasma fusiforme, Haeckel, 1862, Monogr. d. Radiol., p. 404, Taf. xix. fig. 8.
Spines spindle-shaped, from the thicker central part thinned towards the two thin conical ends, perfectly straight and smooth, rigid, inelastic. Central capsule non-transparent, brown.
Dimensions.—Length of the spines 0.3 to 0.5, breadth in the central part 0.006 to 0.009.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific.
4. Acanthochiasma spirale, n. sp.
Spines spindle-shaped, tapering from the thicker central part towards the two thin conical ends, rigid, inelastic; their central part is spirally convoluted in a very peculiar cochlea-like manner, as in Chiastolus amphicopium (Pl. , figs. 3a, 3b). The ten spines are propped one upon another by the central screw. Central capsule dark, opaque.
Dimensions.—Length of the spines 0.2 to 0.3, breadth of the central spiral part 0.01.
Habitat.—Central Pacific, Station 266, surface.