Artophormis barbadensis (Ehrenberg)

Calocyclas barbadensis Ehrenberg, 1873, p.217; 1875, pl.18, fig.8

Artophormis barbadensis (Ehrenberg), Haeckel, 1887, p.1459

Artophormis barbadensis (Ehrenberg), Riedel and Sanfilippo, 1970, p.532, pl.13, fig.5

DESCRIPTION

Cephalis spherical, with thorny surface and a moderate number of small subcircular pores, bearing a loosely spongy (occasionally latticed-bladed) apical horn. Collar stricture pronounced. Thorax inflated-campanulate, with thorny surface and subcircular pores. Lumbar stricture distinct. Abdomen tending to be somewhat longer than thorax and with slightly thinner wall, truncate-conical, with thorny surface and irregular subcircular pores. Fourth segment short, formed of very irregular latticework of which some elements are longitudinal ribs that commonly extend a short distance as free terminal spines. No differentiated termination of fourth segment (Riedel and Sanfilippo, 1970).

DIMENSIONS

Based on 44 specimens. Length of first three segments (excluding horn) 95-145 m. Maximum breadth of the abdomen 70-120 m. Ratio of abdomen length : thorax length 0.8-1.8 : 1 (Riedel and Sanfilippo, 1970).

DISTINGUISHING CHARACTERS

Artophormis barbadensis differs from practically all other four-segmented Cenozoic theoperids by the fourth segment constructed proximally of longitudinal bars connected by discontinuous transverse ones. In A. gracilis, which has a similarly constructed fourth segment, the third segment is inflated-annular rather than truncate-conical (Sanfilippo et al., 1985).

VARIABILITY

The sparsely porous cephalis and inflated-campanulate to hemispherical thorax are relatively constant characters of the species, but otherwise it is quite variable. The third segment is truncate conical, usually longer than the thorax. The fourth segment proximally consists of longitudinal bars connected by discontinuous transverse ones, but distally becomes a less regular lattice. In some specimens the apical structure consists of a few short horns, while in others it is a complex, occasionally spongy structure. Pores of the thorax and abdomen are subcircular, with no prominent alignment, and the shell surface varies from smooth to very thorny (Sanfilippo et al., 1985).

DISTRIBUTION

This species is found in late middle Eocene to earliest Oligocene assemblages from the tropical parts of the Pacific and Indian Oceans, and from the Caribbean region. Its morphotypic first appearance is within the Podocyrtis mitra Zone and it evolves into Artophormis gracilis within the Theocyrtis tuberosa Zone.

PHYLOGENY

The antecedents of A. barbadensis are obscure, but it evolved to A. gracilis just above the Eocene-Oligocene boundary.

REMARKS

Additional illustrations can be found in Riedel and Sanfilippo, 1971, pl.3B, fig.9.

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