Description - Add description
The primary spines and primary arches as in Plectacantha oikiskos. The ventral arch and the left, lateral one also here run together to a strong, basal arch branch from the left, lateral main spine.
Outside the ventral, sagittal spine, there is an extended network of numerous, secondary meshes, which both below and on the sides are connected by the fine transverse beams to a corresponding one on the sides of the dorsal sagittal spine. In this way a network is formed, which is imperfectly closed beneath.
There are numerous byspines. Between these and the larger beams more or less numerous and mostly thin, arch-shaped, connecting beams are extended, which are in their turn here and there connected by similar, arched, fine beams, which at a later stage of development are provided with numerous, fine spines. These are, possibly, later, at any rate to some extent, developed to similar fine connecting arches, which more or less completely envelope the network.
The development of the arches is here further advanced than in Plectacantha oikiskos. From the three branches of the apical spine, arch branches extend, the apical arches, one to the dorsal, basal spine, and two to the primary, lateral arches. These apical arches may at the corners, as well towards the apical spine, as towards the dorsal one and the primary arches, be enveloped by similar arches. Cfr. also Jørgensen 1. c. p. 77.
At a younger stage, this species strongly resembles Plectacantha oikiskos. The ventral, sagittal spine, however, makes it easy to distinguish between them. At an older stage, they are so different that they can hardly be confounded. It is likely that there is more than one species which belongs here.
This form is very interesting, clearly being a connecting one between the groups Plectoidea and Monocyrtida. I formerly considered it to belong to the genus Peridium, and there is hardly any great or important difference in the structure of the genera Peridium and Phormacantha. It seems, however, most practicable to separate the imperfectly latticed forms from those which have a regularly developed lattice work which is closed beneath.
On the other hand, this genus – as more fully explained in the introductory remarks to Nassellaria – forms clearly a transition to the genera Euscenium HCK. and Cladoscenium HCK. When the apical arches are further developed, an enclosed spine will result, a "columella".
The larger forms have a "network", which is about 70µ in height. Rather frequent, though never numerous, in deep water samples.
Rather frequent, though never numerous, in deep water samples.
Distribution: The same as that of Plectacantha oikiskos.
|Benson, 1966, p. 357-359; pl. 23, figs. 24-26:|
Phormacantha hystrix Jørgensen
Peridium hystrix Jørgensen, 1900, Bergens Mus. Aarbog (1899), pp. 76-77.
Phormacantha hystrix Jørgensen, 1905, Bergens Mus. Skrifter, pp. 132-133, Pl. 14, figs. 59-63.
?Plectacantha trichoides Jørgensen, 1905, Bergens Mus. Skrifter, p.132, Pl.13, fig.58.
Test consisting of an ovoid to subcylindrical lattice with large, unequal, subpolygonal pores separated by thin intervening bars. Two to three pairs of large dorsal cephalic pores separated by the straight apical bar of the cephalis generally present. Three to four collar pores present, three if the thin vertical bar is absent; cardinal pores of type B. Apical and vertical spines thin, conical, of variable length. In fully developed individuals the dorsal and primary lateral spines are relatively long and curve gently downward; thin, arch-like bars are present between these spines and the cephalis. Surface of test with short, thin spines or thorns. All spines and intervening bars circular in section. A few rare individuals conforming to Jørgensen’s illustration of Plectacantha trichoides were tentatively identified with this species. They appear to represent incompletely developed specimens of Phormacantha hystrix. They are characterized by a large, thin-barred, oval arch which originates from the apical-lateral arches and extends nearly vertically in a plane perpendicular to the sagittal plane. Secondary arches, not unlike the arches of P. hystrix, are developed between this arch and the primary spines and collar ring. Whether or not a latticed cephalis results from these arches could not be determined.
Measurements; based on 5 specimens from stations 81 and 106: height of cephalis 62-66 µm, maximum breadth 43-55 µm; length of apical spine 5-20 µm, of dorsal and primary lateral spines 31-98 µm.
Remarks. Most of the Gulf specimens placed in this species conform to Jørgensen’s illustration of Phormacantha hystrix. The tests are generally irregular but the presence of long basal spines with arches connecting them with the cepha1 is characteristic. A few specimens are similar to Peridium sp. from the Gulf but differ in the presence of longer basal spines and larger cephalic pores.
Distribution. This species is rare in the Gulf but occurs as far north as station 208. It is present at stations 106, 115, 133, 151, 191, and 192 in the northern Gulf and in the southern Gulf only at five stations, namely, 46, 56, 60, 92, and 93. Its slightly greater frequency and more general occurrence in the northern Gulf may indicate its response to upwelling there.
Jørgensen (1905, p. 132) reports Phormacantha hystrix as rather frequent and Plectacantha trichoides as rare in deep-water samples off the Norwegian coast.