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Spongodiscus biconcavus Haeckel, 1887

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Benson, 1966, p. 214-215; pl. 11, fig. 1; text-fig. 14:

Spongodiscus biconcavus (Haeckel) Popofsky

Spongodiscus biconcavus H., Popofsky, 1912, Deutsche SŘdpolar-Exped., vol. 13, p. 143, P1. 6, fig. 2.

Test a spongy disc, thickened in the center and around the margin, with a definite V-shaped notch in the margin. Center of test appears dark, consists of 8-10 concentric discoidal shells which, however, appear spongy in surface view; remainder of test of a dense spongy structure (text-fig. 14). One specimen observed with about 20 marginal spines, 18-25 Ám in length.

Measurements; based on 30 specimens from stations 27, 46, 60, 64, and 81: diameter of disc 221-400 Ám, of central dark area 58-l35 Ám.

Remarks. Haeckel (l887, p. 577) originally defined but did not illustrate this species. Popofsky identified a species which is the same as the Gulf species in all details as Spongodiscus biconcavus Haeckel. Haeckel did not discuss the notch in the margin of the disc, but Popofsky's illustration shows it; therefore, some doubt exists whether this species is S. biconcavus in the sense of Haeckel, but it is the same as Popofsky's interpretation of the species.

Distribution. This species is cosmopolitan in the Gulf, being absent only at stations 203 and 214. It is rare at all other stations except at 64 and 184 where it is common. Its distribution in part may be controlled by upwelling because it occurs in slightly greater numbers in some areas of upwelling, namely at stations 64, 92, and 99. Its greatest frequency is at station 184 (3.4%); therefore, its distribution is similar to that of other species that show increases at this station as well as at 194. This may reflect its tolerance of higher than average salinity and temperature in this region.
Popofsky (1912, p. 143) reported this species at a depth of 400 meters from three stations in the equatorial Atlantic. Haeckel (1887, p. 577) reported his species from "Challenger" station 265 in the tropical central Pacific. It has not been reported from high latitudes; therefore, it may be confined to tropical parts of the world's oceans.
Benson 1966


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