Pd. Taylor et Fk. Mckinney, AN ARCHIMEDES-LIKE CYCLOSTOME BRYOZOAN FROM THE EOCENE OF NORTH-CAROLINA, Journal of paleontology, 70(2), 1996, pp. 218-229
A distinctive spiral unilaminate cyclostome bryozoan, recently discove
red in the Eocene Castle Hayne Limestone Formation of eastern North Ca
rolina, is described as Crisidmonea archimediformis new species. Colon
ies have a thickened spiral axis bearing systems of bifurcating branch
es. When worn and stripped of their branches, the resistant axes close
ly resemble the familiar screws of the Carboniferous to Permian fenest
rate bryozoan genus Archimedes. However, the Eocene screws are shorter
and become more loosely coiled with growth, corresponding to a helico
spiral rather than a helical form. The paleoenvironment inhabited by C
. archimediformis colonies is inferred to have been on the shallow (<3
0 m depth) margin of an open marine, waveswept embayment. Autozooid di
stribution and the gradient of increasing apertural size from branch r
everse to frontal sides in C. archimediformis resemble those of the li
ving cyclostome Exidmonea atlantica and suggest colonial water current
s that flowed upwards and inwards through the spiral colony. Polyascos
oecia, a genus closely related to Crisidmonea, is shown to be an objec
tive junior synonym of Reteporidea, and the new genus Polyascoeciella
(type species Idmonea foraminosa Reuss) is introduced for species with
exterior-walled gonozooids that were previously assigned to Polyascos
oecia.