A new Upper Devonian cystoid attached to a discontinuity surface

Adocetocystis williamsi Strimple and Koch 1968, n. gen., n. sp., constitutes the third described genus of Callocystitidae bearing a double hydropore. Only Lipsanocystis Ehlers and Leighly and Strobilocystites White previously were known. Adocetoajstis williamsi is further characterized by an ovate theca, four unbranched ambulacra which are apical over most of their length, and an apical mouth, double hydropore and gonopore. The relatively few brachioles of A. wiliamsi, in comparison with Lipsanocystis and Strobilocystites, are compensated for by their great length. Adocetocystis williamsi is part of a biocoenose composed dominantly of echinoderms (cystoids and edrioasteroids) and corals (mostly Aulopora). The organisms of this community are attached to a prominent but laterally restricted discontinuity surface. Features which characterize the discontinuity surface are: (1) an irregular upper surface with rounded limestone knobs; (2) prominent borings (post-lithification); (3) a conspicuous zone of pyrite impregnation; and (4) pebbles of the same bore-marked limestone in channelways between the lime stone knobs. The origin and form of the discontinuity surface might have been organically controlled but, more likely, the surface was produced by subaerial erosion. It is supposed that Adocetocystis williamsi lived in an environment of shallow water with at least moderate current activity. The length of stem developed on any individual was dependent upon the position of attachment in relation to the shape and relief of a limestone knob. Strobilocystites calvini, a cystoid with short brachioles, is found in the same environment as Adocetocystis williamsi, which has long brachioles.