A MIDDLE CAMBRIAN PROTO-CORAL WITH AN ACALCAREOUS, AGGLUTINATED SKELETON

An apparently new form of Cnidarian from the Middle Cambrian, Conasauga Formation, NW Georgia, USA is interpreted as developmentally intermediate between askeletal proto-Zoantharia and early calcareous skeletal corals. It also exhibits characteristics of particular adaptation to benthic, sessile life habit in a shallow subtidal environment.

The present form shows four notable affinities to known forms: 1) a septal pattern strongly comparable to the Rugosa (Tetracorallia); 2) evidence of an oral disc comparable to Anthozoa; 3) a solitary, benthic life; and 4) evidence of an operculum comparable to the Cothoniida.

This form also exhibits the previously unreported attribute of an agglutinated exoskeleton composed of sediment particles in an acalcareous, organic matrix.

It is proposed that this form represents an intermediate developmental stage between askeletal and calcareous skeletal Zoantharia in two respects: 1) exodermal infolding congruent to endodermal mesenteries; and 2) an exoskeleton formed by stable agglutination of sediment particles surrounding the body and within the exodermal folds.

This form is well situated chronologically to represent an essential stage in the evolution of early corals. It fits well in a parsimonious developmental sequence from askeletal form to septate, calcareous-skeletal form.