A SUPRA-ORDINAL CLASSIFICATION OF THE BRACHIOPODA

A new classification of the Brachiopoda is proposed to take into accou nt recent advances in our understanding of the anatomy, shell morpholo gy, ontogeny and phylogeny of the phylum. The use of phylogenetic anal ysis to help rationalize this new information did not obviate the dile mma facing all previous classifications of how best to reconcile fossi l and living data. Over 95 % of all recognized genera are founded on e xtinct species, with the greatest diversity occurring in Cambro-Ordovi cian times when all but two of the 26 major groups constituting the ph ylum first appeared. Only five of these groups survive to the present day, albeit as well dispersed representatives of the early diversity. To compare phylogenies extrapolated from these data, phylogenetic anal yses of Recent and Cambro-Ordovician groups were conducted independent ly by using 55 biological characters for the former group and 69 morph ological (and inferred anatomical) features for the latter; only 12 ch aracters were common to both exercises. The cladogram derived for seve n Recent suprafamilial taxa, with Phoronis and cyclostome and ctenosto me bryozoans as outgroups, is virtually the same as that being obtaine d by studies of the brachiopod genome. It is also largely compatible w ith the cladogram for 33 Cambro-Ordovician suprafamilial taxa with Pho ronis as outgroup. This cladogram has, in turn, been subjected to stra tocladistic tests and has been shown to be consistent with the stratig raphic records of the taxa analysed. A reconciliation of the genealogi es derived from the Recent and Cambro-Ordovician data, represented by 14 taxa and clades (with Phoronis as outgroup), was effected by using the 19 synapomorphies characterizing these groups. The resultant clado gram shows living organophosphatic-shelled lingulids (and discinids) a s a sister group to a clade of all other living brachiopods. This clad e, however, includes the extinct organophosphatic-shelled paterinids a nd the organocalcitic-shelled craniids. The inclusion of the craniids, in particular, is a cladistic compromise that is inconsistent with ge netic and some anatomical and morphological evidence. It was therefore decided to accommodate these inconsistencies by dividing the Brachiop oda into three subphyla, each typified by Recent species with early Pa laeozoic ancestors and defined by easily identifiable synapomorphies. The inarticulated Linguliformea, consisting of two classes (Lingulata and Paterinata), is characterized by an organophosphatic shell with a stratiform secondary layer and by planktotrophic larvae. Its modern re presentatives are the lingulids and discinids. The inarticulated Crani iformea is primarily distinguished by an organocarbonate shell with a laminar secondary layer and the absence of a pedicle throughout ontoge ny. The craniids are the sole Recent descendants. The mainly articulat ed Rhynchonelliformea is the largest subphylum as it embraces five Cla sses (Chileata, Obolellata, Kutorginata, Strophomenata and Rhynchonell ata). Its synapomorphies include an organocarbonate shell with a fibro us secondary layer, the presence of a pedicle without a coelomic core and the development of a recognizable diductor muscle system controlli ng the opening of the valves about a hinge axis defined by interareas. All Recent brachiopod species articulating with cyrtomatodont teeth a nd sockets are rhynchonelliforms.