1. Introduction to Chordates BIO 122: Zoology Newberry College

2. Phylum Chordata Most complex of all phyla All have a notochord rod-like semirigid body of cells usually extends length of body ventral to nervous system’s spine Purposes: 1) support & stiffen body 2) provide skeletal support for muscles

3. Phylum Chordata Five important features of chordates: 1. 1. Notochord 2. 2. Dorsal tubular nerve cord 3. 3. Pharyngeal pouches and gill slits 4. 4. Endostyle 5. 5. Postanal tail

4. Chordate characteristics 1) Notochord - a flexible, rod-like structure * beginning of the internal skeleton * axis for muscle attachment, flexible w/o shortening * in vertebrates the notochord becomes segmented as vertebrae

5. Chordate characteristics 2) Dorsal Tubular Nerve Cord - produced by infolding of ectoderm during early development * in many invertebrates the nerve cord is ventral and solid * in many anterior end becomes swollen = brain

6. Chordate characteristics 3) Pharyngeal Pouches and Gill Slits - perforated openings * lead from pharyngeal cavity to outside body * in simplest aquatic chordates it allows for suspension feeding * in terrestrial organisms is only developmental

7. Chordate characteristics 4) Endostyle - or its derivative, the thyroid gland * in the simplest chordates the endostyle secretes mucus that traps small food particles

8. Chordate characteristics 5) Postanal Tail - extension of body beyond anus * enhances ability for movement (aquatic) & balance (terrestrial)

9. Additional Chordate Features Development pattern as in Echinoderms: radial, indeterminate cleavage deuterostome enterocoelous Segmented muscles in an unsegmented body Complete digestive system Closed circulatory system Endoskeleton made of cartilage and/or bone

10. Classification of Chordates Three distinct Subphyla: Urochordata – tunicates Cephalochordata – lancelets Vertebrata - vertebrates

11. Subphyla of Chordates SUBPHYLUM UROCHORDATA - tunicates Only larval form moves, adults are sessile larvae with all chordate characteristics Adults relatively small, up to a few cm long * produce a leathery outer surface (= tunic) * loss of notochord & tail, nerve cord greatly reduced * become filter feeders with siphons * gills slits become net-like to trap food Individuals are hermaphroditic * reproductive cells into water, external fertilization

12. Diagramatic tunicate

13. Subphyla of Chordates SUBPHYLUM CEPHALOCHORDATA - lancelets Slender, lancet-shaped, 5-7 cm long * sandy bottoms of shallow marine environments Adults clearly with all the chordate characteristics * suspension feeders, trap food in gills slits * circulatory system closed, but no distinct heart * no obvious brain Separate males and females * fertilization external

14. Diagramatic lancelet

15. Subphyla of Chordates SUBPHYLUM VERTEBRATA - vertebrates Very large and diverse group well known due to large size Not all chordate features in adults

16. Characteristics of Vertebrates 1. 1. Expanded endoskeleton - living endoskeleton * internal skeleton, grows with the organism * commonly is hollow, provides support * distinctive covering around brain = cranium

17. Characteristics of Vertebrates 2. 2. Gills in pharynx - better respiration * other subphyla use slits for filter feeding * more active aquatic vertebrates developed gills with muscles * heart developed to enhance circulation

18. Characteristics of Vertebrates 3. 3. Enhanced Nervous System – * with anterior swelling * more complex behaviors of swimmers & predators * has tripartite brain (fore-, mid- and hind-brain) * development of enhanced senses

19. Characteristics of Vertebrates 4. 4. Development of neural crest & ectodermal placode – enhances complexity * neural crest enhances development of skeleton, tooth dentine & endocrine glands * ectodermal placodes enhance sensory development (olfactory, eye, ear)

20. CLASSIFICATION OF VERTEBRATES Several important characteristics to separate: 1) skeleton & jaw composition: cartilage or bony 2) number & structure of paired appendages 3) dermal covering over body 4) relative number of gill slits of an adult 5) type of covering over egg

21. CLASSIFICATION OF VERTEBRATES SUPERCLASS AGNATHA lampreys & hagfish cartilaginous skeleton and no jaw no paired appendages skin smooth (slimy) about 7 gill slits per side eggs with gelatinous covering (aquatic) heart 2-chambered (1 atrium + 1 ventricle)

22. SUPERCLASS AGNATHA Lamprey (note gill slits)

23. CLASSIFICATION OF VERTEBRATES SUPERCLASS GNATHOSTOMATA All other vertebrates with jaws & paired appendages

24. CLASSIFICATION OF VERTEBRATES Class Chondrichthyes (sharks & rays) cartilaginous skeleton and jaw present 2 pair fins placoid scales (tooth like with root) 5-7 pair gill slits eggs with gelatinous covering (aquatic)

25. CLASSIFICATION OF VERTEBRATES Class Actinopterygii (bony ray-finned fish) bony skeleton, jaw present 2 paired appendages; fins overlapping dermal scales (typically thin & flexible) gill slits with covering operculum egg covering gelatinous

26. CLASSIFICATION OF VERTEBRATES Class Amphibia (amphibians) bony skeleton, jaw present 2 paired appendages, legs smooth skin gills only in juvenile forms eggs with gelatinous covering (aquatic)

27. CLASSIFICATION OF VERTEBRATES Class Reptilia (reptiles) bony skeleton, jaw present 2 paired appendages, legs hard scales (snakes) or plates (turtles) gills embryonic only ) eggs with leathery covering (terrestrial)

28. CLASSIFICATION OF VERTEBRATES Class Aves (birds) bony skeleton, jaw present 2 paired appendages; legs + wings feathers + scales on legs gills embryonic only eggs with calcified shell (terrestrial)

29. CLASSIFICATION OF VERTEBRATES Class Mammalia (mammals) bony skeleton, jaw present 2 paired appendages; legs (+ arms) fur and/or hair gills embryonic only viviparous (few with calcified shells)