Description - Add description
Under this name I have entered a form which has the appearance of a species of the division Dicyrtida, but is certainly not fully developed. It is remarkable, as also Haeckel’s illustration, for a rather large cephalis and a short, broad thorax. The spines in the thorax, protruding from the free brim like long, fine spikes are characteristic. Some of these spines are weaker than the others and are branches of them. The cephalis is well supplied with long, needleshaped byspines. There is also a similar apical spine, which here, as in Lithomelissa, is the spine D and runs in the wall of the cephalis, thus not forming any inner columella.
My species differs from Haeckel’s only in the want of byspines on the thorax.
This species occurred very rarely and sparsely in the material from the northern coasts of Norway: 19/1 1899, 40 miles NW of Gaukværø, 0-700 m; 29/1 1899, Malangen, 0-300 m.
Distribution: More frequent on the west coast of Norway, numerous in the Oster Fiord, near Bergen, at a great depth (up to 600 m), 13/6 1900.
Cleve mentions the species from a few places in the Atlantic, west of Ireland and more to the south, as well as from several places far north, to the north west point of Spitzbergen. In these northern places, the species was only found in deep water. Haeckel mentions it from the Azores and the Mediterranean. Hence Cleve considers the species to belong to Styliplankton. It seems, however, judging from the places mentioned where it has been found, to have about the same distribution as Plectacantha, and is probably boreal oceanic.
It is, however, quite possible that Haeckel’s is a distinct species.
|Benson, 1966, p. 375-378; pl.24, figs. 20-21: |
Arachnocorys umbellifera Haeckel
Arachnocorys umbellifera Haeckel, 1861b, Akad. Berlin, Monatab. (1860), pp. 837-838; 1862, Die Radiolarien, pp. 305-306; Pl. 6, fig. 12; Petrushevskaya, 1962, Zool. Zhurnal, vol. 41, pp. 334-336.
Acanthocorys umbellifera Hck. (?), Jørgensen, 1905, Bergens Mus. Skrifter, p. 137, Pl. 18, fig. 107.
Cephalis subspherical to subcylindrical with small, unequal, circular to subcircular pores; with numerous, thin, conical spines some of which are heavy or horn-like and branched distally in several specimens; in a few tests thin, siliceous threads present between a few of these spines (Pl. 24, fig. 21). Cephalis separated from a smooth to slightly spiny, broadly conical thorax by a distinct change in contour. Thorax incompletely developed, not constricted distally, consisting of numerous (7-10 or more) longitudinal ribs originating from the collar ring and an irregular lattice of large, subpolygonal to subrectangular pores separated by thin intervening bars developed between them; the ribs extend distally as thin conical spines; proximally, the lattice is not present between them; instead there are large pores separating them and surrounding the collar ring. Four collar pores present; cardinal pores of type B. Apical bar present as a dorsal cephalic rib which extends as a generally thin, conical apical spine. Vertical spine short, thin, conical or thorn-like; in a few tests a thoracic rib originates from the origin of the vertical spine. Dorsal and primary lateral bars extend as thoracic ribs which terminate in short, thin, conical spines above the base of the thorax; in several specimens the primary lateral bars are also collinear with short thin spines originating from the collar ring.
Measurements; based on 20 specimens from stations 34, 60, 106, 133, and 191: length of cephalis 28-50 µm, of thorax 43-80 µm; breadth of cephalis 28-47 µm, of thorax 68-123 µm; length of apical spine 7-22 µm, of vertical spine 6-12 µm, of accessory cephalic spines or horns 5-35 µm, of dorsal and primary lateral spines 5-l5 µm.
Remarks. A few specimens of this species from the Gulf have a few thin, siliceous threads present between the cephalic spines, but in most tests they are lacking. Arachnocorys circumtexta Haeckel (1861b, p. 837; 1862, Pl. 6, figs. 9-11) differs from A. umbellifera Haeckel in the presence of these thin siliceous threads. The Gulf species, however, is identified with the latter because its rare occurrence prohibits analysis of its complete range of variation. Whether or not it is conspecific with the former could not be determined.
The Gulf species is identical to the illustrations of the species listed in the synonymy. Jørgensen (1905, p. 137) placed this species within Acanthocorys Haeckel because of the lack of siliceous threads between the cephalic spines in the specimens he studied. Results of study of the Gulf specimens, however, show that this character is subject to intraspecific variation. Jørgensen's species rightfully belongs in Arachnocorys Haeckel.
Distribution. This species has a distribution similar to that of Acanthocorys variabilis except that it is nearly common at station 133 and has a recognizable but only slightly greater frequency in the northern half of the Gulf, indicating its possible response to upwelling in this region. It is absent at stations 71, 90, 95, 130, 194, 203, 206, and 214. As in A. variabilis it prefers offshore, more nearly oceanic waters.
This species has been reported from the Mediterranean Sea (Haeckel, 1862, p. 838), in Norwegian fjords, off the west coast of Norway, as far north as Spitzbergen but only in deep waters, from the Atlantic Ocean west of Ireland (Jørgensen, 1905, p. 137), and from the eastern Pacific near California (Petrushevskaya, 1962). Arachnocorys circumtexta Haeckel, which may be conspecific with the Gulf species, was reported by Haeckel, (1887, p. 1266) as cosmopolitan, occurring at the surface in the Mediterranean Sea and in the Atlantic Ocean at "Challenger" stations 347-354. The Gulf species, therefore, is apparently cosmopolitan.