Systematics and biogeography of burrowing bryozoans

Current investigations of the three principal families of ectoproct bryozoan burrowers has shown that while two of the families, the Terebriporidae and the Immergentiidae, belong to the minor Order Ctenostomata, the third family, Penetrantiidae, previously considered a ctenostome, actually belongs to the major Order Cheilostomata. The implications of this are important; we have considered the burrowing bryozoans to be a small obscure group, specialized for the burrowing mode of existence. We must now consider the possibility that there may be many more species of burrowing bryozoans as yet undiscovered, that they occur in at least two of the three bryozoan orders, and that burrowing constitutes an important ecological niche or mode of adaptation for the bryozoans. While such a change may seem to be merely a taxonomic maneuver, itmay also serve to emphasize the diversity of the ectoproct bryozoan groups which do burrow, and perhaps encourage research on them. At present we are making progress describing the living species, their anatomy and histology. We still know almost nothing about how they penetrate the substrate, nothing about possible effects upon the host organism, and nothing about their means of geographical distribution, although they seem to occur worldwide, burrowing primarily in molluscan shells.