(A) Phylogenetic tree of peptidoglycan recognition proteins (PGRPs). With the exception of Remipedes, PGRPs were not found in Crustaceans. PGRPs have been found in Arthropods, including insects, Myriapods and Chelicerates. (B) Phylogenetic tree of Toll-like receptors (TLRs) generated from five Crustaceans, three Hexapods, two Chelicerates, one Myriapod and one vertebrate species. (C) Genomic organization of the Parhyale Dscam locus showing the individual exons and exon arrays encoding the immunoglobulin (IG) and fibronectin (FN) domains of the protein. (D) Structure of the Parhyale Dscam locus and comparison with the (E) Dscam loci from Daphnia pulex, Daphnia magna and Drosophila melanogaster. The white boxes represent the number of predicted exons in each species encoding the signal peptide (red), the IGs (blue), the FNs and transmembrane (yellow) domains of the protein. The number of alternatively spliced exons in the arrays encoding the hypervariable regions IG2 (exon 4 in all species), IG3 (exon 6 in all species) and IG7 (exon 14 in Parhyale, 11 in D. pulex and 9 in Drosophila) are indicated under each species schematic in the purple, green and magenta boxes, respectively. Abbreviations of species used: Parhyale hawaiensis (Phaw), Bombyx mori (Bmor), Aedes aegypti (Aaeg), Drosophila melanogaster (Dmel), Apis mellifera (Amel), Speleonectes tulumensis (Stul), Strigamia maritima (Smar), Stegodyphus mimosarum (Smim), Ixodes scapularis (Isca), Amblyomma americanum (Aame), Nephila pilipes (Npil), Rhipicephalus microplus (Rmic), Ixodes ricinus (Iric), Amblyomma cajennense (Acaj), Anopheles gambiae (Agam), Daphnia pulex (Apul), Tribolium castaneum (Tcas), Litopenaeus vannamei (Lvan), Lepeophtheirus salmonis (Lsal), Eucyclops serrulatus (Eser), Homo sapiens (H.sap). Both trees were constructed with RAxML using the WAG+G model from multiple alignments of protein sequences created with MUSCLE.