A Pacific Tabulate Sponge, Living Representative of a New Order of Sclerosponges Willard D. Hartman Thomas F. Goreau a Pacific Tabulate Sponge, Living Representative of a New Order of Sclerosponges

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. POSTILLA 167: 21 p. 20 MAY 1975 Thomas F. Goreau, who was Professor of Marine Sciences at the University of the West Indies, Mona, Kingston, Jamaica, Professor of Biology at the State University of New York at Stony Brook and Director of the Discovery Bay Marine Laboratory, Discovery Bay, Jamaica, died unexpectedly in New York on 22 April 1970. This paper, based largely on specimens collected by Professor Goreau and enriched by his observations of the organism in life, was prepared by the first-named author.