radiolaria - rads_cenozoic - Phormocyrtis proxima radiolaria - rads_cenozoic - Phormocyrtis proxima

Phormocyrtis proxima

Classification: rads_cenozoic -> Pterocorythidae -> Phormocyrtis -> Phormocyrtis proxima
Sister taxa: P. alexandrae, P. cubensis, P. embolum, P. ligulata, P. proxima, P. striata, P. turgida, P. sp.


Citation: Phormocyrtis proxima Clark & Campbell 1942
Rank: species
Basionym: Phormocyrtis proxima

Catalog entries: Phormocyrtis proxima

Original description: Shell smooth, with the maximum diameter well up on the thorax, as a whole little swollen and with slight (or no) apertural contraction, surface strongly ribbed; apical horn rather short, more like a spike than a distinct horn (its length sometimes only about 0.5 length of cephalis), conical in outline, mostly thin but sometimes (Fig. 26) stout, equally four-bladed, with four fins, the tip sharp, basally merged to the top of the cephalis; cephalis conical (70° decreased to 20° in the basal 0.5), the top caplike, the sides spreading, the base chiefly distinguished by sudden change in lateral shell contour at its junction with the thorax, its sides not markedly convex, often distinctly asymmetrical, the blades of the horn continued down the sides nearly to the base; thorax with narrowly rounded (73°) shoulder reaching a maximum diameter of 0.15 greater than the length of the thorax itself near the middle, thence gradually contracting (30°) or sometimes continued in the lower thorax as a cylinder (Fig. 26), the lower margin of the thorax itself, this lower level marked by an internal, horizontal, narrow, septal band; abdomen inverted truncate-conical in its upper portion, thence subcylindrical with slightly concave sides, and with an undulant, truncate, circular margin whose diameter is nearly 0.5 the maximum diameter of the thorax; wall uniform, trim, and rather thick; general surface and pore characters almost exactly as in the related species P. ligulata n. sp., in the lower stratigraphic horizon.

Length of shell, 190µm (tipped); of horn, 21.0µm; of cephalis, 25.4µm; of thorax, 80.4µm; diameter of maximum, 91.4µm; of aperture, 51.8µm; of thoracic pores, 4.4µm. Distinguishing characters (rw): Two specimens are illustrated in the writers' material. One of these (Fig. 26) has subparallel sides on the lower thorax and the abdomen, and a stout apical horn. This specimen is possibly crushed and unusual. Much more typical is the other (Fig. 24) individual.
Phormocyrtis proxima n. sp. differs from P. ligulata n. sp. in contour, and especially in the subcylindrical lower abdomen. The shell is not spindlelike in general shape, although the wall structure is similar in the two species.
Remarks on original description: [Synonymized with Phormocyrtis embolum by Riedel, 1957a]


Biogeography and Palaeobiology

Biostratigraphic distribution

Geological Range:
Last occurrence (top): within Paleogene Period (23.03-66.04Ma, top in Chattian stage). Data source: Lazarus et al. 2015 - "P age group"
First occurrence (base): within Paleogene Period (23.03-66.04Ma, base in Danian stage). Data source: Lazarus et al. 2015 - "P age group"

Plot of occurrence data:



Phormocyrtis proxima compiled by the radiolaria@mikrotax project team viewed: 5-6-2023

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