| Home> Miocene>

List species

Helotholus? haysi Lazarus, 1992

Description - Add description

Small, cap-shaped shell with very small, indistinct hemispherical cephalis and short cylindrical thorax. Lattice wall of both cephalis and thorax thin, with (relative to size of shell) large, irregularly shaped, irregularly distributed pores; bars thin, thorny, surface of shell rough. Horizontal ring inside thorax, connected to thorax wall by 7-10 radial beams, and to base of caphalis by vertical beams.

Differs from the similar form H. vema in its small size, in having more radial beams (H. vema usually has 6 or 7), relative to the diameter of the thorax, in having a larger internal ring, and, in general, in having more variable morphology (irregularly shaped, noncircular internal rings, etc.). Lazarus (1990) noted the presence of a form in the basal Pliocene and Miocene of the Weddell Sea region that appears, at least in part, to be the same species, although the Pliocene specimens from the Weddell-Sea region are much larger than those from the Kerguelen Plateau and may not be conspecific. The generic assignement of this species, and of H. vema, is uncertain. H. haysi appears to be congeneric with H. vema, as it differs from H. vema only in such details as lattce wall texture, number of internal beams, and overall size. Kellogg (1975) postulated an evolutionary origin for H. vema (which she calls Pseudocubus vema) from a form that Weaver (1983) named as a new species, Helotholus praevema. I have been unable to distinguish H. praevema from other members of the genus Antarctissa. It seems likely that the generic definition of Antarctissa will need to be revised, and these two species transferred to Antarctissa. See also comments in Lazarus (1990).
Lazarus 1992











Discussion / Comments


Web links