Additions to the Genus Phyllodesmium, with a Phylogenetic Analysis and its Implications to the Evolution of Symbiosis

The facelinid genus Phyllodesmium (Ehrenberg, 1831) consists of approximately 24 described species that prey upon soft-bodied corals. At least five additional species have yet to be described, making it an interesting genus for testing phylogenetic hypotheses. The genus is extremely morphologically diverse, with many species adapting specifically to a specific host coral. One of the most interesting adaptations found in this genus is the widespread participation in a symbiotic relationship with photosynthetic dinoflagellates in the genus Symbiodinium. Two new species, Phyllodesmium acanthorhinum n. sp. and Phyllodesmium undulatum n. sp., from the Philippine Islands and Japan are described, and a morphological phylogeny is created to include the two new species, as well as three undescribed species. An examination of the Phyllodesmium phylogeny suggests that species with digestive gland branching and zooxanthellae are more derived. Confidence and robustness in this analysis are lacking, however, and further studies using molecular data could add confidence to this conclusion.