Phylogenetic Relationships Among Extant Brachiopods

Abstract

Abstract— The monophyletic status of the Brachiopoda and phylogenetic relationships within the phylum have long been contentious issues for brachiopod systematists. The relationship of brachiopods to other lophophore‐bearing taxa is also uncertain; results from recent morphological and molecular studies are in conflict. To test current hypotheses of relationship, a phylogenetic analysis was completed (using PAUP 3.1.1) with 112 morphological and embryological characters that vary among extant representatives of seven brachiopod superfamilies, using bryozoans, phoronids, pterobranchs and sipunculids as outgroups. In the range of analyses performed, brachiopod monophyly is well supported, particularly by characters of soft anatomy. Arguments concerning single or multiple origins of a bivalved shell are not relevant to recognizing brachiopods as a clade. Articulate monophyly is very strongly supported, but inarticulate monophyly receives relatively weak support. Unlike previous studies, the nature of uncertainties about the clade status of Inarticulata are detailed explicitly here, making them easier to test in the future. Calcareous inarticulates appear to share derived characters with the other inarticulates, while sharing many primitive characters with other calcareous brachiopods (the articulates). Experimental manipulation of the data matrix reveals potential sources of bias in previous hypotheses of brachiopod phylogeny. Although not tested explicitly, lophophorate monophyly is very tentatively supported. Molecular systematic studies of a diverse group of brachiopods and other lophophorates will be particularly welcome in providing a test of the conclusions presented here.

Molecular evidence that phoronids are a subtaxon of brachiopods (Brachiopoda: Phoronata) and that genetic divergence of metazoan phyla began long before the early Cambrian

“…It is well supported and was previously reported by Carlson (1995) on the basis of a cladistic analysis of morphological characters. This suggests that the current treatment of craniiforms as a separate subphylum (Williams et al 1996) is unjustified; they would be better regarded as a class, equivalent in rank to phoronids and lingulates.…”

“…Because of the large divergence between sponge and bilaterian SSU sequences, the sponge was used only in some preliminary analyses intended to explore and define the problems and potentialities of the data. Because of the wealth of information available on brachiopod evolutionary biology (Kaesler 1997(Kaesler -2002 and in press), failure to recover key relationships (Rowell 1982;Carlson 1990Carlson , 1995Gawthrop 1996, 1997;Kaesler 1997-2002 andin press;Cohen et al 1998a, b;Cohen 2001) could be used to identify analyses yielding suboptimal topologies. These expected relationships were: (1) that articulate brachiopods should (a) be the sister-group of inarticulate brachiopods and (b) divide into two subclades, one with a loop, the other without; (2) that discinid and lingulid inarticulate brachiopods should form a clade.…”

Neuromuscular development in Novocrania anomala: evidence for the presence of serotonin and a spiralian‐like apical organ in lecithotrophic brachiopod larvae

“…This view is supported by molecular analyses based on 18S rDNA sequences, which either place the craniiforms within the linguliforms (Cohen 2000) or as the direct sister-group to the linguliforms (Cohen and Weydmann 2005). Other morphological characters such as the presence of an anus and a lophophore without internal mineralized support underpins a close relationship of craniiform and linguliform brachiopods (Carlson 1995). However, based on the lecithotrophy of the larvae and the presence of a calcareous shell in the adults, craniiform brachiopods have been proposed to be closer related to the rhynchonelliforms rather than to the linguliforms, which have a free-swimming planktotrophic life cycle stage that closely resembles the morphology of juvenile brachiopods (Nielsen 1991).…”

Changes in the timing of mantle formation and larval life history traits in linguliform and craniiform brachiopods

“…Cohen & Gawthrop ( 1997) have carried out a molecular phylogenetic analysis of living brachiopods based on the small subunit of rDNA. Carlson (1995) has done a cladistic analysis on living brachiopods. Their work shows that the discinids, lingulids and craniids, which are distributed in two separate subphyla in the new classification, are much more closely related to each other than they are to the rh ynchonelliforms.…”