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Peridium sp. cf. P. longispinum Benson, 1966

Description - Add description

Benson, 1966, p. 362-363; pl. 24, figs. 4-5:

Peridium sp.

Test consisting of a spiny, ovoid cephalis, similar in shape to that of Peridium longispinum but with larger, polygonal, unequal pores and without an external neck lattice. Collar ring with 3-4 collar pores, four if vertical bar is present; when present, vertical bar is very thin, cardinal pores of type B. Apical bar a straight, dorsal cephalic rib with large pores paired on either side of it; it extends as a thin, conical apical spine of variable but generally short length. Vertical spine short, thin, conical or thorn-like. Dorsal and primary lateral bars extend as thin, conical spines, each with a pair of small conical branches arising from near their origin. A short (6-12 µm) axial spine present in many specimens. No specimen was observed without thin, conical spines arising from the nodes of the intervening bars of the cephalis. A few specimens have lateral ribs in the cephalic wall, similar to those of Peridium longispinum.

Measurements; based on 15 specimens from stations 106 and 192: length of cephalis 49-80 µm, maximum breadth 34-76 µm; length of apical spine 6-18 µm, of dorsal and primary lateral spines 18-62 µm.

Remarks. This species was placed in the genus Peridiurn because it is similar in shape and size to Peridium longispinum Jørgensen. Several specimens are very similar to the latter species but lack the external neck lattice and have larger polygonal pores and shorter dorsal and primary lateral spines. Several tests are similar to Phormacantha hystrix Jørgensen, but they are distinguished by shorter dorsal and primary lateral spines with a pair of branches arising from near their origins and the lack of small, arch-like bars developed between the spines and the cephalis. These differences may be artificial in that forms intermediate between this species and the two species mentioned above may exist; therefore, a new name is not proposed for this taxon.

Distribution. In the Gulf this species is absent north of station 151. It occurs rarely at this station as well as at stations 34, 46, 56, 60, 64, 81, 91, 92, 93, 95, 106, 115, 133, and 136. It has a greater frequency in the northern part of its range at stations located within the diatomite facies of the Gulf and apparently responds to upwelling only in this region.
Benson 1966











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