Archaeocyatha: More on Morphology

While they display a variety of growth forms, from disk-like to branching, the typical archaeocyath skeleton resembles two ice-cream cones, one inside the other, connected by vertical and sometimes horizontal plates, septa and tabula respectively. The ESEM (environmental scanning electron microscope) image to the left shows the the outer wall and inner wall of one specimen connected by six septa. The ESEM micrograph to the right shows an outerwall and two septa. The space between the inner and outer walls is termed the intervallum. Nearly all of the primary skeletal elements (e.g., inner walls, outer walls, septae, and tabulae) are perforated by small pores. Archaeocyaths were attached to the substrate by a basal holdfast consisting of several prongs, or more commonly, a solid mass. Archaeocyath fossils range in size from as small as a millimeter to well over one-half meter, but typically are on the order of one to three centimeters. Skeletal material consists of interlocked microgranular polyhedra of calcium carbonate (presumably calcite) with randomly oriented axes, and spicules are lacking.