1. The Phylum Chordata This phylum has 3 subphyla - Urochordata
- Cephalochordata
Craniata
Chordates are deuterostomes
(sensu strictu)
Possess four unique characteristics

2. 1) Dorsal Hollow Nerve Cord
Forms from a dorsal ectoderm tube
Forms the CNS (brain & spinal cord)
Other animal phyla have ventral solid nerve cord(s)

3. 2) Notochord Longitudinal, flexible cartilagenous rod
Located between nerve cord and gut

4. 2) Notochord Extends most of the length of the organism
A simple ENDOSKELETON
For some chordates this is all they have (thus ‘invertebrate’ chordates)
VERTEBRATE chordates develop a more complex jointed skeleton
BUT vertebrates still have vestiges of the notochord (intervertebral discs !)

5. 3) Pharyngeal Slits
Early chordates – these connected to the digestive tract; used for FILTER FEEDING
Later became modified for gas exchange
Present (vestigial) in our early embryo stage

6. 4) Postanal Tail

7. 4) Postanal Tail
Digestive tract extends most of the body length in the majority of non-chordates
Tail extends beyond the anus in chordates
Contains skeletal elements
Contains muscles
Major propulsive force in many aquatic chordates
Other uses for the tail ?????

8. Subphylum Urochordata
Invertebrate chordates
Called Tunicates (some called sea squirts)
Tunic is made of a cellulose-like carbohydrate called tunicin
Filter Feeders
Free swimming as larvae
Sessile as adults (adhere by ‘head’ region to objects)

9. Subphylum Urochordata
Highly modified as adults
Scarcely resemble other chordates
During metamorphosis they lose the tail, notochord & nerve cord (‘brain’ atrophies)
Retain pharyngeal slits
Closed circulatory system
Possess heart & blood cells (no hemoglobin)
Most primitive of the chordates (?????)

10. Subphylum Urochordata (larva)

11. Subphylum Urochordata (adult)

12. Subphylum Cephalochordata
Lancelets
Laterally compressed

13. Subphylum Cephalochordata
Adults somewhat resemble urochordate larvae
All 4 chordate traits persist
Filter feeders; tentacles around mouth
Marine; burrow tail first
Feeble swimmers; fish-like movements (sinusoidal)
Serially arranged muscle segments

14. Origin of Craniates & Vertebrates
Fossils – resembling Cephalochordates – Burgess Shale of British Columbia ~550mya
Craniates and Vertebrates first appear during the Cambrian “explosion” ~ 530mya
Early Craniates and Vertebrates possessed all four chordate characteristics and were filter feeders
Probably derived from a Urochordate-like ancestor similar to a tunicate larva
Paedogenesis resulted in a larva achieving sexual maturity and it did not undergo metamorphosis

15. Paedogenesis
Precocious attainment of sexual maturity in a morphologically juvenile organism
If successful, natural selection would have reinforced the absence of metamorphosis
These larvae were active and natural selection would favor the most active
Actively foraging organisms benefit from good sense organs
Cephalization is a benefit

16. Craniate / Vertebrate Characteristics
All possess the four basic chordate traits (at least at some stage)
Cephalization with a highly specialized brain
The brain is covered by or enclosed by a skull
MOST Craniates possess a vertebral column that encloses the nerve cord
MOST possess jaws
Skeleton is an endoskeleton

17. The Endoskeleton Composed of cartilage, bone or both
Grows with the organism
Cells secrete and rearrange the matrix
AXIAL SKELETON - skull plus vertebral column (plus ribs & breastbone, if present)
APPENDICULAR SKELETON may be present (supports fins or limbs)

18. Additional Traits (I) Closed circulatory system
Heart with 2, 3 or 4 chambers
Arteries, capillaries, veins
Red blood cells (with hemoglobin) for O2 transport
Blood oxygenated through skin or more commonly via gills or lungs

19. Additional Traits (II)
Possess kidneys (compact excretory structures)
Reproduction usually sexual
Dioecious (= unisexual)
Gender control variable (XY, WZ, environmental)
Some can change gender
Parthenogenesis found in most classes (but not common)

20. Subphylum Craniata Nine or ten extant classes Mixini Petromyzontidae
Chrondrichthyes
Antinopterygii, Actinistia, Dipnoi
Amphibia
Reptilia
Aves (?)
Mammalia

21. The Agnathan Classes (I)
Oldest fossilized craniates were agnathans
Mud-suckers/filter feeders
Living forms lack paired appendages and external armor
No covers for gill slits
Two-chambered heart
Class Mixini (hagfishes)
Class Petromyzontida (lampreys)

22. The Agnathan Classes (II)
Hagfishes (30 species) are eel shaped
Lack rasping mouthparts
Some feed on sick or dead fish or on worms
Marine
Skull of cartilage
No vertebrae (are “craniate invertebrates”)

23. Hagfish

24. The Agnathan Classes (III)
Lampreys (about 35 species) are eel shaped
Young are usually suspension (filter) feeders
Young live in freshwater
Adults usually marine but some stay in freshwater
Adults have rasping mouth parts
Attach to live fish and are parasitic
Possess a cartilaginous tube around the notochord with pairs of projections (Vertebrae); thus a “craniate vertebrate”)

25. Lamprey (I)

26. Lamprey (II)

27. Lamprey (III)

28. The First Gnathans Classes Placodermi and Acanthodii (extinct)
Possessed hinged jaws and paired fins
Jaws developed from skeletal rods supporting some of the more anterior pharyngeal slits
Jaws allow for more varied feeding habits
Vertebrate jaws work UP and DOWN (arthropod jaws work Side to Side)
Remaining slits functioned as major gas exchange sites

29. Basic Craniate (from text)

30. Development of Jaws (from arch supports 3 & 4)

31. Jaws and Supports

32. Acanthodian

33. Placoderm

34. Class Chondrichthyes (I)
The cartilaginous fishes (about 750 species)
Lack of bone in skeleton is considered a derived condition
Sharks, rays, skates, and more
No swim bladder
Must swim to stay up in the water column
Some have added buoyancy due to large amounts of oil stored in the liver

35. Class Chondrichthyes (II)
Marine animals – evolved in the sea
Paired fins, well-developed jaws; most are carnivores (a few filter feeders)
No opercula (external gill covers)
Scaled; Teeth evolved from modified scales
Reproduce sexually; fertilization internal; dioecious
Oviparous, Ovoviviparous or Viviparous
Claspers on male’s pectoral fins transfer sperm into the female’s reproductive tract

36. Class Chondrichthyes (III)
Cloaca present
Heart two-chambered
Short digestive tract; spiral valve present
Good vision but no color vision
Sharks have a fusiform body
Rays and skates are dorsoventrally flattened

37. Black Tipped Reef Shark

38. Ray

39. The “Bony” Fishes
Formerly in one class (Osteichthyes) but now divided into three classes
Cloaca absent in all three classes; dioecious; heart is 2-chambered
Class Actinistia – coelacanths (believed to have been extinct for 65 million years) – Two (?) extant species; a lobe-fin group that evolved in freshwater and then moved to the ocean
Class Dipnoi – lungfishes – another lobe-fin group; 3 genera and 7 species; Freshwater; use lungs for respiration; Gave rise to tetrapods

40. Coelacanth

41. Dipnoi (Australian Lungfish)

42. Class Antinopterygii Largest group of vertebrates (~30,000 spp)
Most of our familiar fish species
Body covered by flattened bony scales
Evolved in freshwater; many moved to the ocean; some have returned to freshwater
A few species spend a portion of their lives in freshwater and in saltwater
Possess a swim bladder for buoyancy – it developed from lungs

43. Rainbow Trout 43

44. Evolution of lungs & Swim Bladder

45. Gas Exchange in Fishes
Chondrichthyes – swimming important – forces water into mouth and out over gills
Bony Fish – water drawn into mouth and forced out over gills by movement of the OPERCULUM and contraction of muscles within the gill chambers