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Amphirhopalum ypsilon Haeckel, 1887

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Benson, 1966, p. 221-222; pl. 11, figs. 5-6:

Amphicraspedum wyvilleanum Haeckel

Amphicraspedum wyvilleanum Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 523, P1. 45, fig. 12.

Discoidal test consisting of a circular central region composed of 3-6 latticed concentric rings lying between two parallel latticed plates and with two arms, oppositely placed, one of which is forked distally, with or without a layered spongy patagium between them and covering the two surfaces of the test. Arms thicker than central region of test; internally consisting of concentric latticed partial rings, equally spaced, perpendicular to the two parallel lattice-plates which cover the arms. Rings of one arm, if traced in a circle to other arm, would coincide with homologous rings of the latter; 5-10 rings in both arms, number dependent on degree of development of individual test. Pores of the lattice-plates subequal, circular to subcircular, arranged in concentric rows, 2-3 rows in the area between rings.

Measurements; based on 30 specimens from stations 46, 60, 64, 71, and 81: maximum length of test 198-338 Ám; maximum breadth of patagium (17 specimens) 96-219 Ám; diameter of outer ring of central area 46-92 Ám (3-6 rings); length of unforked arm 55-141 Ám, of forked arm 62-139 Ám; maximum breadth of unforked arm 71-129 Ám, of forked arm (including branched arms if present) 77-172 Ám.

Remarks. Incompletely developed forms of this species have both arms unforked, and in many specimens the patagium is absent or rudimentary. No fully developed forms have both arms forked; thus Amphicraspedum rnaclaganium Haeckel (1887, p. 523, P1. 45, fig. 11) is a separate species. Monaxonium perforatum Popofsky (1912, p. 126, P1. 6, fig. 3) is similar in form to this species, but Popofsky's illustration shows that the arms appear to be composed of numerous caps (similar to Zygocampe chrysalidium) instead of rings between flat, latticed plates.

Distribution. This species is cosmopolitan in the Gulf, being absent only at stations 203, and 214. It is rare at all stations but is present in slightly greater numbers at stations located in the axial portion of the Gulf. Its average frequency is slightly greater in the southern half of the Gulf; therefore, it is a more nearly oceanic species. It undergoes no marked increase at stations located within regions of upwelling.
This species was reported by Haeckel (1887, p. 523) from "Challenger" station 333 at approximately 35░ S. latitude in the south central Atlantic. It has not been reported from high latitudes.
Benson 1966


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