Morrowan lithistid demosponges and hexactinellids from the Ozark Mountains of northwestern Arkansas

Abstract

Silicified and well-preserved specimens of the new orchocladine anthaspidellid genus and species, Virgaspongia ichnata, the rhizomorine haplistiid, Haplistion sphaericum Finks, 1960, and various root tufts, and the new hexactinellid species Steioderma hadra are reported from the Brentwood Member of the Morrowan Bloyd Formation from the Sulphur City quadrangle, in the Ozark Mountains of northwestern Arkansas. Virgaspongia is a subcylindrical branched or unbranched sponge that lacks a spongocoel and has a dendroclone-based skeleton in which trabs diverge upward and outward from an axial region. It is abundant here but is one of only a few anthaspidellid genera known from the Pennsylvanian. This is the first record of Haplistion from Pennsylvanian rocks of Arkansas, although the genus is widespread in upper Paleozoic rocks. The new hexactinellid species, Stioderma hadra, also documents the first occurrence of that genus from Arkansas and in Morrowan rocks. Only fragments were recovered but the swollen grotesque spicules, of several sizes, that make the fused dermal layer and outer sponge wall are distinctive, particularly where combined with an inner layer(?) or root tuft of monaxons of various sizes. Two different root tufts and one demosponge wall fragment(?) also occur in the collection.