Classification of CA-like amino acid sequences from Daphnia pulex. Phylogenetic trees for selected α-carbonic anhydrases (α-CAs) (A) and β-CAs (B) based on multiple-sequence alignments (Additional files 1 and 2). D. pulex sequences are shown in red; underlined labels indicate EST support. Three fragmentary sequences (CAA6A, CAA7B, CAA7L; Table 4) from D. pulex were excluded from the alignment. Additionally included were related sequences from the blue crab Callinectes sapidus (Cs), Drosophila melanogaster (Dm), Anopheles gambiae (Ag), Caenorhabditis elegans (Ce), sea urchin Strongylocentrotus purpuratus (Sp), Homo sapiens (Hs), the sea anemone Nematostella vectensis (Nv), and Pisum sativum (Ps). α-CAs were classified in terms of their putative destination into mitochondrial and cytoplasmic, CA-related, membrane-bound and transmembrane, and secretory proteins. CA-related proteins have lost most of the highly conserved active-site residues. Membrane-associated α-CAs have a C-terminal attachment signal for a glycosylphosphatidylinositol (GPI) anchor which tethers the extracellular protein to the cell membrane . The trees were constructed using the neighbor-joining algorithm. Bootstrap analysis was performed with 1000 replicates (bootstrap values > 800 are indicated by filled circles). For sequence references, see Additional files 1 and 2.