Family XXXIII. Astrolophida, Haeckel

Suborder I. Actinelida, Haeckel, 1882.

Definition.—Acanthometra with a variable number of radial spines, which are commonly irregularly disposed, not according to the Icosacantha.

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.

The first observed form of this family is the ancestral genus Actinelius, two different species of which I detected in 1864 in the northern Mediterranean, at Villafranca, near Nice (compare Zeitschr. f. wiss. Zool., 1865, Bd. xv. p. 364, Taf. xxvi. fig. 4). Three other species of the same genus were afterwards found by me in the Challenger collections. Whilst in this Actinelius all radial spines are of the same size, a new nearly allied genus, Astrolophus (with two species), differs from it by the different size of the radial spines, a small number of very large spines being intermingled with a very large number of small spines. In these two genera, Actinelius and Astrolophus (the true "Astrolophida" sensu strictiori), the number of the radial spines is quite indeterminable and their arrangement quite irregular and variable.

A third remarkable genus, Actinastrum, differs from these two genera in the definite number and regular order of thirty-two radial spines, and may therefore perhaps better represent a peculiar family, Actinastrida. In this genus (of which two species were observed) the thirty-two radial spines are disposed in such a regular manner that they lie in four meridian planes, and that their distal ends fall into five parallel zones. These five zones and these four planes are the same as we find in all Icosacantha (compare above, p. ). Also the constant twenty spines of these latter are present in Actinastrum; but their number is here enlarged by twelve other spines missing in the Icosacantha; four of these are secondary or interradial equatorial spines, lying opposite in pairs between the four primary or perradial equatorial spines; and eight are perradial tropical spines, lying between the eight interradial tropical spines. Therefore the distal ends of the thirty-two radial spines are disposed regularly in five parallel zones, and while two zones (the two polar) contain only the points of every four spines, three zones (the single equatorial and the two tropical) contain the points of every eight spines. The four meridian planes are in Actinastrum the same as in the Icosacantha, crossed in the spineless axis at angles of 45°. But in the Icosacantha each of the two perradial meridian planes contains six radial spines (two equatorial and four polar), each of the two interradial meridian planes only four tropical spines. Whereas in Actinastrum each of the two primary or perradial meridian planes contains ten spines (two equatorial, four tropical, and four polar), each of the two secondary or interradial meridian planes six spines (two equatorial and four tropical). We find therefore altogether thirty-two radial spines in three orders; eight equatorial, sixteen tropical, and eight polar spines.

Only one other genus of Radiolaria exhibits the same characteristic disposition of thirty-two radial spines as Actinastrum, and this is Chiastolus; but here the two opposite spines of each pair are grown together and form one diametral spine; and the sixteen diametral spines are crossed in the centre of the capsule. In Actinastrum, as in Astrolophus and Actinelius, the central ends or bases of all the spines are pyramidal, and the triangular faces of the neighbouring spines rest one upon another (as in the greater number of Acanthonida). The form of the radial spines in all Astrolophida is quite simple, without lateral processes or apophyses; chiefly cylindrical, more rarely compressed, two-edged or quadrangular.

The central capsule in all Astrolophida is spherical, and in the younger specimens contains a single large concentric and lobed nucleus, but in the older specimens a large number of small nuclei. The surrounding jelly-veil or calymma seems commonly to envelop the spines perfectly. The piercing pseudopodia radiate everywhere between the spines, and are very numerous and thin. The circulating granules in them are sometimes red (Actinelius purpureus).

Synopsis of the Genera of Astrolophida.

Radial spines of indefinite number and of irregular disposition. Spines of equal size, 317. Actinelius.

Spines of unequal size, 318. Astrolophus.

Radial spines thirty-two, disposed regularly in five parallel zones, 319. Actinastrum.

Radial spines of indefinite number and of irregular disposition.

Spines of equal size,

317. Actinelius.

Spines of unequal size,

318. Astrolophus.

Radial spines thirty-two, disposed regularly in five parallel zones,

319. Actinastrum.

Genus 317. Actinelius, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364.

Definition.—Astrolophida with a variable and undetermined number of simple radial spines, all of equal size, united in the centre of the spherical central capsule.

The genus Actinelius comprises the most simple and primitive forms among all Acantharia, and may be regarded as the common ancestral stock of this whole legion. The spherical central capsule is pierced by numerous simple radial spines of equal size, the pyramidal bases of which are supported one upon another with their triangular faces in the centre of the capsule. The number and position of the spines are quite indefinite and variable. We may derive Actinelius either from Actissa (Colloidea) by development of acanthinic radial spines, or directly from Actinosphærium (Heliozoa) by formation of a central capsule.

Subgenus 1. Actinelarium, Haeckel.

Definition.—Radial spines cylindrical, conical, or spindle-shaped, their transverse section circular.

1. Actinelius primordialis, n. sp. (Pl. , fig. 1).

Spines sixty to eighty or more, cylindrical, at the distal end thickened, spindle-shaped. Apex simple. Base a small slender pyramid. Central capsule yellow. Granules of the sarcode colourless.

Dimensions.—Length of the spines 0.3 to 0.4, breadth in the distal part 0.02, in the basal part 0.008.

Habitat.—Central Pacific, Stations 265 to 274, surface.

2. Actinelius purpureus, Haeckel.

Actinelius purpureus, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364, Taf. xxvi. fig. 4.

Spines thirty to forty or more, cylindrical, very thin, a little thinner towards both ends. Apex simple. Base a small sulcate pyramid. Central capsule opaque, purple. Granules of the sarcode also purple.

Dimensions.—Length of the spines 0.2 to 0.3, breadth 0.002.

Habitat.—Mediterranean (Nice), Haeckel.

Subgenus 2. Actinelidium, Haeckel.

Definition.—Radial spines compressed, two-edged; their transverse section elliptical or lanceolate.

3. Actinelius protogenes, n. sp.

Spines fifty to sixty, compressed, two-edged, gradually broadened towards the truncated distal end. Basal or proximal end thin, pyramidal. The spines of this species are similar to those of Actinastrum pentazonium (p. ) and of Chiastolus amphicopium (Pl. , fig. 3), but much more numerous, smaller, and not regularly disposed. These latter two Actinelida must be separated on account of the regular disposition of the thirty-two spines.

Dimensions.—Length of the spines 0.2, basal breadth 0.008, distal breadth 0.02.

Habitat.—South Pacific, Station 165, surface.

Subgenus 3. Actinelonium, Haeckel.

Definition.—Radial spines quadrangular, prismatic, or pyramidal, their transverse section square.

4. Actinelius pallidus, Haeckel.

Actinelius pallidus, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364.

Spines eighty to one hundred and twenty or more, quadrangular, prismatic, of equal breadth throughout their whole length. Apex simple, truncate or pyramidal. Base a four-sided slender pyramid. Central capsule pale yellowish. Granules of the sarcode colourless.

Dimensions.—Length of the spines 0.2 to 0.3, breadth 0.005.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific.

5. Actinelius polyacanthus, n. sp.

Spines two hundred to three hundred or more, quadrangular, pyramidal, gradually thinned towards the simple apex. Base a small three-sided pyramid. Central capsule opaque.

Dimensions.—Length of the spines 0.12 to 0.18, basal breadth 0.012.

Habitat.—South Pacific, Station 291, surface.

Genus 318. Astrolophus, Haeckel, 1881, Prodromus, p. 469.

Definition.—Astrolophida with a variable and undetermined number of simple radial spines of different sizes (large and small spines intermingled), which are united in the centre of the spherical central capsule.

The genus Astrolophus differs from the nearly allied ancestral genus Actinelius only in the unequal size of the numerous radial spines. In both observed species very numerous small spines are intermingled with a small number of large spines, and between them numerous spines of medium size. The small spines fill up the hollow spaces between the basal parts of the large spines.

1. Astrolophus stellaris, n. sp.

Radial spines from one hundred to two hundred, of very different sizes, but of similar form; about sixteen to twenty very large spines, forty to fifty of medium size, and one hundred to one hundred and twenty much smaller. All spines cylindrical in the greater part of their length, with simple apex, gradually thickened towards the central part, conical, without edges. The base itself is a slender pyramid with four to eight edges.

Dimensions.—Length of the largest spines 0.3 to 0.4, of the majority 0.1 to 0.2, of the smallest 0.05 to 0.1.

Habitat.—South Pacific, Station 288, surface.

2. Astrolophus solaris, n. sp. (Pl. , figs. 12a, 12b).

Radial spines from two hundred to three hundred, of very different sizes, but of similar form; about twenty to thirty very large spines, sixty to eighty of medium size, and one hundred and twenty to one hundred and fifty much smaller. All spines cylindrical in the greater part of their length, with simple apex, gradually thickened and four-edged towards the central base. The base itself is a slender pyramid with four to eight edges; partly the faces, partly the edges of these basal pyramids rest one upon another, the points of the larger spines meeting in the centre.

Dimensions.—Length of the largest spines 0.4 to 0.5, of the majority 0.2 to 0.3, of the smallest 0.1 to 0.16; basal thickness of the largest spines 0.015.

Habitat.—South-east Pacific (off Juan Fernandez), Station 296, surface.

Genus 319. Actinastrum, n. gen.

Definition.—Astrolophida with thirty-two simple radial spines, regularly disposed within four meridian planes in such an order that their distal ends fall into five parallel zones. Central ends of the thirty-two spines supported one upon another in the centre of the spherical central capsule.

The genus Actinastrum differs from the two preceding genera in the definite number and order of the thirty-two radial spines, which are disposed in a very remarkable manner. Twenty radial spines are disposed after the Müllerian law of Icosacantha (compare above, p. ). The remaining twelve spines are four equatorial spines lying in the two secondary meridian planes, and eight tropical spines lying in the two primary meridian planes. We have therefore together eight equatorial, sixteen tropical, and eight polar spines (compare above, p. ).

1. Actinastrum legitimum, n. sp.

All thirty-two radial spines of equal size and similar form, cylindrical, conical at the distal end, at the central base pyramidal. Central capsule pellucid, colourless.

Dimensions.—Length of the radial spines 0.3, breadth 0.004.

Habitat.—South Pacific, Station 288, surface.

2. Actinastrum pentazonium, n. sp.

All thirty-two radial spines of equal size and similar form, compressed, two-edged, gradually becoming broader and thinner from the pyramidal central base towards the truncated distal end. Central capsule dark, opaque. (Compare the similar Chiastolus amphicopium, Pl. , fig. 3.)

Dimensions.—Length of the radial spines 0.2, breadth at the base 0.005, at the distal end 0.02.

Habitat.—South Pacific (west coast of Patagonia), Station 302, surface.