Tadpole
A tadpole is the aquatic larval stage of a frog or toad, usually bearing a tail and gills before metamorphosis into a four-limbed adult.
Amphibian metamorphosis: A developmental transformation in amphibians from a larval form to a distinct juvenile or adult form. It reorganizes tadpole body systems, including the limbs, tail, lungs, and feeding apparatus.
Anura: The amphibian order comprising frogs and toads, characterized as adults by the absence of a tail. Tadpoles are the larval stage of animals in this order.
Xenopus: A genus of aquatic frogs widely used in developmental biology and laboratory research. Xenopus tadpoles are accessible models for studying vertebrate development and metamorphosis.
Common frog: A widespread European frog species, Rana temporaria, that breeds in freshwater. Its familiar black-spotted tadpoles develop in ponds and shallow waters.
Thyroid hormone: A hormone that regulates metabolism and development in vertebrates. Thyroid hormone signaling triggers and coordinates many changes during tadpole metamorphosis.
Amphibian: A vertebrate in the class Amphibia, whose life cycles commonly involve aquatic and terrestrial stages. Frogs and toads are amphibians, and their larvae often develop in water.
Tadpole assay: A laboratory test using tadpoles to measure biological responses to chemicals or environmental conditions. Researchers use tadpoles to assess developmental effects and aquatic toxicity.
American bullfrog: A large North American frog, Lithobates catesbeianus, whose larvae can remain aquatic for an extended period. Bullfrog tadpoles illustrate how larval duration differs among frog species.
Gill: A respiratory organ that extracts dissolved oxygen from water. Tadpole gills support aquatic respiration before lungs and other breathing modes take over.
Larva: An immature animal stage that differs substantially from the adult form. A tadpole is a specialized larval form rather than a small adult frog.