A new sclerosponge, Acanthochaetetes wellsi, with a calcitic skeleton made up of contiguous vertical tabulate calicles ornamented within by vertical rows or irregular clumps of spines is described from cryptic habitats on reefs in the western Pacific region. A lamellar microstructure characterizes the calicle walls and spines. Increase in number of calicles occurs as intramural offsets. An epitheca with growth lines surrounds the entire sponge. Living tissue is restricted to the space in the calicles above the outermost tabulae and a thin layer lying above the calcareous skeleton. Siliceous spicules of two kinds, tylostyles and modified spirasters, are distributed in the living tissue but are not incorporated into the calcitic skeleton. Star-shaped groups of exhalant canals converge upon central oscules on the sponge surface and leave astrorhizal patterns impressed into the calcareous skeleton below. A new order, the Tabulospongida, of the class Sclerospongiae is proposed to receive the new Pacific species together with its Jurassic and Cretaceous forebears. Despite suggestive similarities between acanthochaetetids and favositids, a phylogenetic relationship between these two groups is considered unlikely on the basis of present evidence.