Evidence from Hox genes that bryozoans are lophotrochozoans

Bryozoans, or moss animals, are small colonial organisms that possess a suspension-feeding apparatus called a lophophore. Traditionally, this phylum has been grouped with brachiopods and phoronids because of the feeding structure. Available molecular and morphological data refute this notion of a monophyletic Lophophorata. Alternative hypotheses place bryozoans either at the base of the Lophotrochozoa or basal to the Lophotrochozoa/Ecdysozoa split. Surprisingly, the only molecular data bearing on this issue are from the 18S nuclear ribosomal gene. Here we report the results of a Hox gene survey using degenerate polymerase chain reaction primers in a gymnolaemate bryozoan, Bugula turrita. Putative orthologs to both the Post2 and the Lox5 genes were found, suggesting that bryozoans are not a basal protostome group but closely allied to other lophotrochozoan taxa. We also found the first definitive evidence of two Deformed/Hox4 class genes in a nonvertebrate animal.