Table 3.

Summary of retinoic acid receptor (RAR) functions in marine invertebrates.

Taxon	Clade	Phylum	Receptor Activity	Developmental Function
Deuterostomia	Chordata	Tunicata	Ligand-activated by retinoic acid	Neurogenesis, budding
		Cephalochordata	Ligand-activated by retinoic acid	Neurogenesis, axial patterning
	Ambulacraria	Echinodermata	Ligand-activated by high concentrations of retinoic acid	Presumably involved in developmental growth
Protostomia	Ecdysozoa	Priapulida	Ligand-activated by high concentrations of retinoic acid	Unknown
		Hexapoda	Absent from the genome	RA with role in nervous system regeneration, tissue repair
	Lophotrochozoa	Annelida	Ligand-activated by high concentrations of retinoic acid	Neurogenesis
		Mollusca	Ligand-binding pocket occluded and potential activation by liganded RXR	Neurogenesis
Non-Bilateria	Radiata	Cnidaria	Absent from the genome	RA with role in neurogenesis, metamorphosis, strobilation