Coleolus carbonarius Demanet, 1938 (incertae sedis) from the late Bashkirian (Carboniferous) of the Donets Basin

Abstract

Problematic fossils Coleolus carbonarius Demanet, 1938 were described from seven localities of the Mospyne Formation (late Bashkirian, Carboniferous) of the central Donets Basin. Many authors attributed these conoidal fossils to various groups of animals, including worms, conulariids, pteropods, hyoliths, tentaculitids, gastropods, scaphopods, and other molluscs without specifying the class, as well as phyllocarids. Representatives of the genus Coleolus cannot belong to the scaphopods because the apex of their tube is closed. The aperture of the tube in living Coleolus is directed upwards, while in scaphopods it is directed downwards. The belonging of Coleolus to pteropods was challenged by previous authors. The assignment of Coleolus to Coniconchia is also incorrect, because the shells of Coniconchia have chambers, which are absent in Coleolidae. The ecological and some morphological characteristics of Coleolus indicate their proximity to sedentary polychaete annelids (Sedentaria) or phoronids (Phoronida). Almost all Coleolus remains come from sediments that formed in a shallow marine environment with a low sedimentation rate and contamination of the bottom silt and, possibly, the bottom layer of the water column with hydrogen sulphide. Coleolus carbonarius, according to all of the obtained data, was a semi-infaunal animal. The apical end of the tube was deeply immersed into the semi-liquid clayey silt. Only a small part of the tube protruded above the surface. The characteristic transverse ornament of the tube surface, possibly, increased the contact area of the unstable semi-liquid clayey silt and the tube and further stabilized the vertical position of the animal in the bottom sediment. The sedentary lifestyle of Coleolus apparently suggests that these animals fed on planktonic organisms and organic detritus suspended in the water column. This type of feeding is possible only in the presence of a developed hunting apparatus. The morphology of the tubes of Coleolus carbonarius Demanet, 1938 is described in the article, including the structure of their apical end and aperture. Traces of damage caused during the lifetime of animals on the apical part of their tube are also studied.