Significance of epibionts on horn corals from the Chainman Shale (Upper Mississippian) of Utah

Epibionts Tolypammina? sp. (Protozoa), Eridopora sp. (Bryozoa), Petrocrania sp. (Brachiopoda), Spirorbis? sp. (Annelida), and Vermiforichnus sp. (Annelida) on the curved conical coralla of Barytichisma sp. (Coelenterata) show a strong preference for the concave side of the corallum and are more abundant on the upper half of the corallum than on the lower half. This distribution helps confirm Bernard's (1904) hypothesis that the corallum assumed a living position lying on its side, after topping from an early attached upright growth position, and curved upward from the substrate in order to maintain an optimum living position later in life. The distribution also indicates that these epibionts inhabited the host coralla mostly while the polyps were alive. Thallophyta (algae or fungi) and Bascomella sp. (Arthropoda) established themselves on the host coralla later than the other epibionts and have a random distribution with respect to the plane of curvature, indicating that these organisms inhabited the hosts mainly after the death of the polyps.