Figure 1.

Phylogeny and morphology of green hydra Hydra viridissima. (A) Phylogenetic position of H. viridissima (red) within the phylum Cnidaria. (B) Relationship of Hydra viridissima strain A99 (red) with other H. viridissima strains and brown hydra species, based on phylogenetic analysis with the NJ method using cytochrome c oxidase subunit I (COI) gene sequences. The genomic region in H. viridissima A99 and Genbank IDs in other strains used in the phylogenetic analysis are indicated. (c) Photographs of H. viridissima (left) and H. vulgaris (right). H. viridissima is smaller than H. vulgaris, and green due to symbiotic Chlorella in its endodermal epithelial cells.