Lecture 17: intro to chordates

Chordate characters

Bilateral symmetry, anterior posterior axis, complete gut, coelom, metamerism, Cephalization, Deuterostomes

Protochordata

Not monophyletic, urochordata (tunicates) and cephalochordata (lancelets) Invertibrates chordates

Urochordata

Tunicates, sessile some free living, have tunic (test) surrounding them, larva have chordate halmarks

Cephalochordata

Lancelets, slender laterally compressed, sandy sediments of coastal waters lack brain and vertebrae

Notochord

Flexible rod like body of fluid filled cells enclosed by fibrous sheath, organizational role in nervous system development

Dorsal hollow nerve cord

Dorsal to digestive tract and notochord, nerve cord is hollow in craniates anterior end becomes brain and passes through vertebrae

Pharyngeal pouches/slits

Openings leading from pharyngeal cavity to the outside

Pharyngeal pouches/slits Protochordates

Perforated pharynx functions as filter feeder

Pharyngeal pouches/slits Aquatic chordates

Bear gills used in gas exchange

Pharyngeal pouches/slits Tetrapods

Pouches only present in embryonic stage, become many structures (eustachian tube, middle ear cavity, tonsils, and parathyroid gland)

Endostyle

In protochordates and lamprey larvae, secretes mucus to trap food brought into pharyngeal cavity cells secrete iodinated proteins

Thyroid gland

Adult lampreys and other vertebraetes, regulates metabolism

Postanal tail

In protochordates for motility in humans only during development and vestigial

Chrodata

Protochordata and craniata

Craniata

Gnathostomata and Agnatha

Gnathostomata

Teleostomi and chondrichthyes

Agnatha

Myxini (hagfish) and petromyxontida (lampreys)

Chondrichthyes

Sharks, rays, and chimaeras

Osteichthyes (bony fish)

Actinopterygii (ray finned fishes) and sarcopterygii (lobe finned fishes)

Tetrapods

Amniota and amphibia

Modern amphebians

Gymnophiona (caecilians), urodela (salamanders), Anura (frogs)

Amniotes

Reptilian and mammalian, monophyletic amniotic membrane around embryo, lack gilled larvae, internally fertilize

Reptilia

Testudines (turtles), lepidosauria (tuataras and squamata), archosauria (crocodilians and birds)

Paleognathae

Large flightless birds, no sternum with poorly developed pectoral muscles

Neognathae

All other birds, nearly all fly, kneeled sternum with lots of flight muscles

Monotremes

Egg laying mammals

Marsupials

Pouched animals

Placental mammals

Every other mammal but pouched and egg laying