Table 2.

Summary of thyroid hormone receptor (THR) functions in marine invertebrates.

Taxon	Clade	Phylum	Receptor Activity	Developmental Function
Deuterostomia	Chordata	Tunicata	Unknown	Suspected role in metamorphosis
		Cephalochordata	Activated by TRIAC	Pivotal regulator of metamorphosis
	Ambulacraria	Echinodermata	Presumably ligand-activated and/or controlled by alternative signaling pathways	Suspected role in growth, metamorphosis, skeletogenesis
Protostomia	Lophotrochozoa	Annelida	Ligand-activated by T3 or TRIAC	Regulator of developmental transition from trochophore to crawling larva
		Mollusca	Presumably ligand-activated and/or controlled by alternative signaling pathways	Suspected role in growth and developmental transitions
		Platyhelminthes	Presumably ligand-activated and/or controlled by alternative signaling pathways	Suspected role in growth
Non-Bilateria	Radiata	Cnidaria	Absent from the genome	THs with a role in metamorphosis, strobilation, skeletogenesis