Benson 1966 - Heliodiscus asteriscus

Benson, 1966, p. 200-210; pl. 9, fig. 3 (not fig.4): Heliodiscus asteriscusHeliodiscus asteriscus Haeckel,1887, Challenger Rept., Zool., vol. 18, p. 445,. P1. 33, fig. 8.Cortical shell discoidal, with equal to subequal, circular to subcircular, regularly arranged pores, 12-21 (generally 16-18) across the diameter, generally without polygonal frames but frames rudimentary in a few tests; surface smooth to thorny, in several specimens with thin, conical spines. Margin of shell with 5-30 or more, relatively long, broad, conical to three-bladed spines, generally lying in a single plane, not continuous inwards as beams; in one specimen 20-30 smaller, less robust marginal spines present in addition to the heavier spines; spines generally of nearly equal length in each specimen but of unequal lengths in several. Medullary shell subspherical to ellipsoidal or globular, with relatively large, subequal, circular to subcircular pores, 5-8 on the half circumference; joined to cortical shell by numerous (15-30 or more) thin, cylindrical radial beams none of which reach the margin of the cortical shell; some beams continue as thin, conical spines beyond the surface of the cortical shell.

Measurements: based on 30 specimens from stations 27, 34, 46, 56, 60, and 71: major diameter of cortical shell 119-191 µm, of medullary shell 47-64 µm; length of marginal spines 6-129 µm (generally 25-50 µm).

Remarks: Several species of Heliodiscus illustrated by Haeckel are similar to H. asteriscus, but without access to Haeckel stypematerial, their synonymy with this species is not proposed. These includeH. polymorphus Haeckel (1887, p. 447, P1. 34, figs. 11, 12) andpossibly H. solaster Haeckel (1887, p. 447, P1. 34, fig. 4) and H. echiniscus Haeckel (1887, p. 448, P1. 34, fig. 5).H. asteriscoides Haecker(1908, p. 444, P1. 83, figs. 578-580)differs from H. asteriscus in thepresence of numerous, long, thin, conical spines arising from the surface of the cortical shell (observed in a few Gulf specimens) but morefundamentally in the presence of a large circular pylome in the medullary shell.

Distribution: This species is of cosmopolitan but rare occurrence in the Gulf. It is absent only at stations 151, 203, and 214 and is common (3.0%) only at station 194.Other than at this station it undergoes no abrupt changes in its frequency. In the absence of known upwelling near station 194, it must be concluded that the increase in this species at this station is due to its tolerance of waters with slightly higher than average temperature and salinity. Its cosmopolitan occurrence in the Gulf also suggests this. It has a slightly greater abundance in the southern Gulf. Haeckel (1887, p. 445) reports this species as cosmopolitan at the surface and various depths from all oceans, including the Mediterranean Sea. The species of Haeckel mentioned in the remarks were reported from the central Pacific.H. asteriscoides Haecker (1908, p. 444) was reported from the northern Indian Ocean, as well as from the South Atlantic at station (128) located in the West Wind Drift. Whether or not this species is trulycosmopolitan at all latitudes must await further taxonomic study.

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