Article: Immunological investigations of relationships with the terebratulid brachiopods

Intra-crystalline macromolecules isolated from the skeletons of nine species of Recent articulate brachiopods were compared by enzyme linked immunosorbent assay (ELISA) to assess the relationships within the Order Terebratulida (Phylum Brachiopoda, Class Articulata). Immunological distance data indicated that the sub-division of this order into three suborders (based on the characteristics of the internal skeleton, particularly the brachial loop) is not valid. Three major clusters were recognized within the Terebratulida which approximately correspond to recognized superfamilies, with the exception that the family Kraussinidae (possessing a long brachial loop) is placed within the Terebratulacea (characterized by a short loop). The three lineages are more closely related to each other than was previously predicted, and yet within most lineages there is a greater degree of subsequent diversification than has hitherto been recognized. The independent evolution of long brachial loops in two lineages identified by the immunological data, highlights problems with using the internal skeleton as a high-level taxonomic character within the terebratellids.