Phylum: Chordata

1. Phylum: Chordata

2. All chordates have (at some point) • A notochord • A dorsal hollow nerve cord • Gill slits • Muscle blocks • Bilateral symmetry • Coelom • Segmentation • Not all of these characteristics are apparent in adult organisms and may appear only in the embryonic or larval stages.

4. Chordates: Can be with or without a backbone • Invertebrate Chordates – Sea Squirts (tunicates), Lancelets • Vertebrate Chordates – Birds, fishes, mammals, amphibians, reptiles

5. 1. Notochord • a flexible, rodlike structure • Extends the length of the body and is an anchor point for muscles – allows for powerful movement • In invertebrate chordates and the jawless vertebrates (ex. Lamprey) the notochord is present throughout life (no backbone) • However, in the jawed vertebrates it is replaced by the vertebral column (the backbone)

6. 2. Dorsal Hollow Nerve Cord (DHNC) • Develops from ectoderm that rolls into a hollow tube • The anterior end of nerve cord is enlarged in vertebrates into a brain • The posterior end of the nerve cord is the spinal cord.

8. 3. Gill Slits • Gills slits are paired openings in the pharynx/behind the mouth • The gill slits are used as a filter feeding device in sea squirts and lancelets • Gills slits in fish develop into internal gills • Gills slits disappear in humans as they develop

9. Humans – embryonic gill slits

10. Lancelet

12. 4. Muscle Blocks • Modified body segments of stacked muscle layers • Muscle blocks anchor to the notocord • Fish meat = muscle blocks • Muscle blocks develop into more developed muscle tissue in humans and other animals

13. Lancelet – V shaped muscle blocks

14. Fish muscle blocks

15. 5. Bilateral Symmetry:a single plane divides body into two mirror images

16. 6. Body Cavity: Coelom • The coelom is a cavity entirely surrounded by mesoderm. • A coelom provides a tube-within-a-tube arrangement which has many advantages: • Allows visceral organs to grow independently of the body wall

18. 7. Segmentation • Divided into a series of parts

19. 8. Tail an extension of the body past the anal opening • The postanal tail allows some organisms to swim and its efficiency has been enhanced by the addition of fins. • The postanal tail is present only in vestigial form in humans (the coccyx) although tails as a whole are widespread among vertebrates.

20. Subphyla: Urochordata • Urochordates- example: tunicates or sea squirts • Invertebrate chordates p. 796 Fig. 29.9 • Tunicates exhibit the dorsal hollow nerve cord, notochord, gill slits and muscle block in the larval (immature) stage. • Sessile and colonize as adults—gillslits are the only chordate characteristic maintained as an adult. • Filter feeds

23. Synoicum pulmonaria  a colonial sea squirt

24. Subphylum: Cephalochordata • Cephalochordata- example: lancelets p. 707 Fig. 29.10 • Invertebrate chordates • Exhibit notochord, dhnc, muscle block and gill slits throughout their life • filter feed

25. Lancelets • small (3-7 cm long) fishlike animals that inhabit sandy sediments of coastal waters. • They lack a distinct head and have no cranium. • There are 29 species, five of which occur in North American coastal waters.

27. Subphylum: Vertebrata • Vertebrata-fish, amphibians, reptiles, birds and mammals • Exhibit notochord, dhnc, muscle blocks and gill slits at some point of development. • dorsal hollow nerve cord becomes the spinal cord • notochord becomes the backbone (vertebral column) • gill slits present in all embryos and maintained in fish and some amphibians and reptiles at different stages of development. • muscle blocks and tail present embryonic in all vertebrates, present in the adult form in some vertebrates

28. Chordates have sophisticated equipment including . . . • a closed circulatory system with a multi-chambered heart • bilateral symmetry with lots of cephalization (and sophisticated sense organs) • an internal skeleton that grows with us • an extraordinary immune system • a digestive tract with lots of specialized portions