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Amphymenium amphystylium Haeckel, 1887

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Amphymenium amphystylium
Both arms equal, three times as long as broad, thickened towards the truncated distal end, and armed with a strong pyramidal terminal spine. Each arm with seven joints, separated by convex, transverse septa, and halved by a radial beam lying in the longitudinal axis. Patagium incomplete, cylindrical, enveloping only the middle part of the shell.
Dimensions -Radius of each arm 0.18, greatest breadth 0.06; transverse breadth of the patagium 0.08.
Habitat.-North Atlantic, Station 354, surface.
Haeckel 1887
Amphymenium amphystylium
Description. Shell with two opposite pored chambered arms arising from a central structure composed of a single spherical medullary shell and an irregular cortical shell. Arms increase in diameter distally, as few as 7, but generally 9 to 13; chambers bearing randomly placed subcircular pores on each arm; surface rough with occasional thornlike projections. Shell may become spongy at the distal end of the arms. Termination blunt, but in some specimens there are strong pyramidal terminal spines at the end of each arm. The central structure and the proximal chambers on each arm are surrounded and partly obscured by a spongy cylindrical patagium. There may also be an outer pored, spindle-shaped patagium surrounding all but the last 1 to 3 chambers and constricted distally so as to join the main part of the shell. Surface of secondary patagium smooth. Haeckel (1887) described this form as having only 7 chambers on each arm and he did not describe the outer patagium.
Dimensions (based on 20 specimens). Maximum length of shell = 190-290 Ám; maximum width of arms = 34-60 Ám; minimum breadth of arms, excluding patagium = 20-30 Ám; breadth of arms, including patagium = 50-52 Ám.
Distinguishing characters. This species is distinctive in that it is relatively long compared to its width. The arms, unlike those of A. splendiarmatum, are chambered.
Remarks. The relationship between this species and Amphymenium splendiarmatum Clark and Campbell (1942, p. 46, pl. 1, figs. 12, 14) is not clear. The principal difference noted by Clark and Campbell is that A. splendiarmatum lacks distinct chambering on the arms. A. splendiarmatum has been reported primarily in Paleogene sediments, although Nishimura (1987) records a similar form from the middle Miocene that also apparently lacks chambers on the arms. Until the relationship between these forms is understood, we prefer to retain the specific name amphistylium for the North Pacific Miocene form. Petrushevskaya and Kozlova (1972) placed the genus Amphymenium in synonymy with Ommatocampe Ehrenberg, but subsequent authors have not followed this suggestion.

Morley and Nigrini 1995


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