Early Chordates and Jawless Fishes

Vocabulary flashcards covering key concepts from the lecture on Early Chordates and Jawless Fishes, including characteristics of chordates, vertebrate specializations, early fossil evidence, and extant jawless fish.

Chordata

An animal phylum that includes Vertebrata, characterized by having a notochord, dorsal hollow nerve cord, post-anal tail, pharyngeal pouches/slits, and an endostyle at some point in their lives.

Notochord

A rod-like, flexible structure found in all chordates at some point in their lives, providing skeletal support.

Dorsal hollow nerve chord

A tubular bundle of nerves located dorsally to the notochord in all chordates at some point in their lives.

Post-anal tail

A tail that extends posterior to the anus, present in all chordates at some point in their lives.

Pharyngeal pouches/slits

A set of openings or grooves in the pharynx, present in all chordates at some point in their lives, used for filter feeding or respiration.

Endostyle

A ciliated groove on the floor of the pharynx, involved in filter feeding, present in all chordates at some point in their lives.

Urochordates

Non-vertebrate chordates, also known as tunicates or sea squirts. Larvae are motile and possess all chordate characteristics, while adults are sessile and lose most features.

Cephalochordates

Non-vertebrate chordates, also known as lancelets (e.g., Amphioxus), which are filter-feeding, fish-like organisms typically buried in the sand.

Vertebrata (Vertebrates)

A subphylum within Chordata, named for vertebrae; characterized by a cranium, tripartite brains, sensory organs, complex endocrine organs, and mineralized tissues.

Vertebrae

Skeletal elements that form a centrum around the notochord during development; true vertebrae are typically found in gnathostomes.

Gnathostomes

A group of jawed vertebrates that possess true vertebrae.

Cranium

A protective bony or cartilaginous structure that encloses the brain, a key characteristic of vertebrates.

Craniata

An alternative or sometimes synonymous name for Vertebrata, emphasizing the presence of a cranium in all members, including hagfish and lampreys.

Homeobox (Hox) genes

Genes that control much of embryonic development; vertebrates have significantly more Hox genes than other animals, contributing to the evolution of complex structures.

Neural crest tissue

A unique fourth germ layer found only in vertebrates, developing into diverse structures like craniofacial bones, the peripheral nervous system, and pigment cells; considered a major evolutionary innovation.

Myllokunmingia

The earliest known true vertebrate, dating back ~525 MYA in the Cambrian Period, possessing features like segmented muscles and a notochord.

Ostracoderms

Bony, jawless vertebrates covered in armor, which proliferated in the Ordovician period; recognized as a paraphyletic group.

Hagfish (Myxiniformes)

Extant jawless fish inhabiting cold marine waters, known for producing large amounts of slime, having a tongue with keratinized teeth, and lacking paired appendages or true vertebrae.

Lampreys (Petromyzontiformes)

Extant jawless fish found in marine and freshwater, many species are parasitic, latching onto hosts; they lack paired appendages and true vertebrae.