evolutionary context

cephalachordata

a group of small filter-feeding marine chordates commonly called lancelets that bury themselves in sand and possess all major chordate characteristics

thyroid gland

an endocrine gland that develops from the endostyle in vertebrates and produces hormones containing iodine for metabolic regulation

notochord

a flexible rod-like structure that runs along the dorsal side of the body and provides structural support and as an attachment point for muscles in early verts and chordates

olfactores

a group of chordates that posses olfactory sense organs for smelling, including vertebrates and tunicates but excluding cephalochordates

dorsal hollow nerve chord

a tubular nerve structure located on the dorsal side of the body that serves as the central nervous system in chordates

urochordata

a group of marine chordates commonly called tunicates or sea squirts that retain chordate characteristics in their larval from but lose some traits in adulthood

chordata

a phylum of animals characterized by the presence of a notochord, dorsal hollow nerve chord, post-anal tail, endostyle, and pharyngeal slits at some point in their development

blastopore

the opening formed during early embryonic development that becomes either the mouth of anus depending on whether the organism is a protostome or deuterostome

deuterostome

an animal whose anus forms first during embryonic development, with the mouth forming second, including chordates and echinoderms

synapomorphy

a shared derived characteristic that is unique to a particular group of organisms and inherited from their common ancestor

hemichordata

a group of marine deuterostomes commonly called acorn worms that share characteristics with both echinoderms and chordates

gnathostomes

jawed verts that evolved from jawless ancestors and include all fish with true jaws, amphibians, reptiles, birds, and mammals

post-anal tail

a tail structure that extends beyond the anus, providing locomotion and support in many chordate larvae and some adults

endostyle

a mucus-secreting groove located in the pharyngeal chamber that traps food particles and also absorbs iodine from water for hormone production

cyclostomes

a group of jawless fish including lampreys and hagfish characterized by circular mouth openings

ambulaclaria

a group of deuterostomes that includes echinoderms and hemichordates, united by genetic evidence and larval morphology despite different adult forms

pharyngeal slits

openings in the pharynx that function in filter feeding by allowing water to flow through while trapping food particles, present in many chordate and larvae and some adults

echinodermata

a group of marine deuterostomes including starfish and sea urchins that are radially symmetrical as adults and bilaterally symmetrical as larvae

protostome

an animal whose mouth forms first during embryonic development, with the anus forming second, including arthropods, mollusks, and most worms

vestigial strucutre

a structure that has lost most or all of its original function through evolution but remains present in an organism