Spongaster pentas Riedel and Sanfilippo

Spongaster pentas Riedel and Sanfilippo, 1970, p.523, pl.15, fig.3; Riedel and Sanfilippo, 1978a, p.74, pl.2, figs.5-8

DESCRIPTION

Spongy disc usually pentagonal, occasionally hexagonal. Rays from center to marginal angles generally not markedly denser (but usually slightly thicker) than the spongy structure between them. Central area (one-half to one-third of disc diameter) more dense, or thicker, with concentric structure (Riedel and Sanfilippo, 1970).

DIMENSIONS

Diameter 170-290 m (Riedel and Sanfilippo, 1970).

Diameter 170-360 m (Sanfilippo et al., 1985).

DISTINGUISHING CHARACTERS

Spongy disc usually pentagonal, occasionally quadrangular or hexagonal, generally with thickened zones corresponding to the angles (Riedel and Sanfilippo, 1978a) S. pentas is distinguished from S. berminghami by its polygonal rather than bipolar symmetry. It is distinguished from S. tetras by the number of rays in most specimens being greater than four (Riedel and Sanfilippo, 1978a).

VARIABILITY

S. pentas is a spongy disk whose symmetry is usually pentagonal or hexagonal, occasionally quadrangular or heptagonal. It generally has thickened or denser zones (corresponding to the angles) and in the center. The most frequent form has five or six thick or dense lobes with lighter spongy material between them, the outline slightly concave between the lobes. In some specimens there are no such concavities between the lobes, and in some the entire disk appears equally dense (Sanfilippo et al., 1985).

DISTRIBUTION

S. pentas is found in middle Pliocene assemblages from latitudes lower than 40, but it is rare in Indian Ocean sediments. Absent from DSDP Site 206, near New Zealand. Its evolutionary transition from S. berminghami defines the base of the Spongaster pentas Zone. However, its morphotypic first appearance is diachronous by ~0.8 m.y. (younger in the tropical Indian Ocean than in the tropical Pacific Ocean). Its morphotypic last appearance is also diachronous by ~0.8 m.y. (older in the tropical Indian Ocean than in the tropical Pacific Ocean).

PHYLOGENY

S. pentas evolved from S. berminghami and into S. tetras.

REMARKS

Additional illustrations can be found in Riedel and Sanfilippo, 1971, pl.1D, figs.5-7.

Casey et al., 1979 reported the presence of S. pentas in Holocene Gulf of Mexico sediments. They considered it to be part of a relict fauna isolated from pan-tropical distribution by the uplift of the Isthmus of Panama.

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