These reciprocal tBLASTn searches produced clear evidence for protostome syndecan and tenascin, suggesting that these ECM proteins may have evolved on the triploblastic stem lineage.
Characterizing the molecular stress-response repertoire of Nematostella can be informative at four levels: (1) comparisons to triploblastic animals and non-animal models will help us to reconstruct the early evolution of stress-response pathways; (2) comparisons to species with narrower environmental tolerances, especially closely related marine anemones, will help us to understand the genomic basis for Nematostella's hardiness and ability to survive in estuarine habitats; (3) comparisons among genetically and phenotypically distinct populations of the starlet sea anemone can reveal the microevolution of stress-response pathways; and (4) identifying molecular markers of stress will augment our ability to utilize Nematostella and other Cnidaria as environmental sentinels.
Comparing the genomic complement of stress genes in Nematostella and Triploblastica will help illuminate the stress-response system of early animals, perhaps revealing the importance of transcriptional control, a primary difference between stress-response pathways in triploblastic animals and other eukaryotes (e.
The evolutionary distance is considerable between the diploblastic, radially symmetrical cnidaria and the triploblastic
bilateral phyla of both deuterostomes and protostomes.
The grouping of the dicyemids with the triploblastic animals was supported by a bootstrap value of 100% in both the neighbor-joining (Fig.
To corroborate the inclusion of the dicyemids in the triploblastic lineage, we analyzed subsets of taxa shown in the present paper as well as several different sets of taxa including some of the following species (the accession numbers for 18S rDNA data are shown in parentheses): Cryptomonas phi (X57162).
The present molecular phylogenetic study based upon comparisons of nucleotide sequences of 18S rDNA shows that triploblastic animals form a monophyletic assemblage within the metazoan subtree and that the dicyemid mesozoa are an ingroup of the monophyletic unit of triploblastic animals.