Chordates and Fishes

1. Chordates and Fishes

2. Chordate Characteristics Characteristics of Chordates • A chordate is an animal that in some stage of development has: • Notochord- dorsal rod of specialized nerves • A dorsal hollow nerve cord- tube just above the notochord • Pharyngeal pouches- small out pockets of the anterior gut (may become gills in some animals) • Postanal Tail-a tail that extends beyond the anus

3. Characteristics Continued • Notochord exists only in the embryo • Notochord replaced by an endoskeleton • In lower chordates (fishes amphibians) pharyngeal pouches evolved into gill slits • In terrestrial vertebrates pharyngeal pouches evolved into structures in throat and ear

4. Classification Phylum Chordata has 3 subphyla • Urochordata-Tunicates • Cephalochordata-Lancelets • Vertebrata Subphylum Urochordata • Hollow barrel shaped Urochordates are commonly called Tunicates and Sea Squirts

5. Subphylum Cephalochordata • Marine organism (usually shallow water) • Best represented by a blade-shaped, animal called a lancelet

6. Subphylum Vertebrata • Brain protected by an outer skull and spinal cord protected by vertebrae • Organs of vertebrates are organized into 10 systems Skeletal, muscular, integumentary, digestive, respiratory, circulatory, excretory, immune, nervous, and reproductive

7. Characteristics of All Vertebrates • Bilateral symmetry • Two pairs of jointed appendages such as limbs or fins • Cephalization with complex brains and sense organs • True coelom lined with mesoderm • Closed circulatory system-blood in vessels and heart • Chambered heart • Either ectothermic (cold blooded) or endothermic (warm blooded)

8. Vertebrate Classes • Fish • Amphibians • Reptiles • Birds • Mammals

9. Classes of Fish • Agnatha-Jawless Fish • Chondrichthyes-Sharks Skates and Rays 3. Osteichthyes-bony fish • Fishes are the most numerous of all vertebrates and most widespread in their distribution

10. Adaptations of Fishes • Swimbladder-adaptation for buoyancy- traps gas inside their body: gas swim bladder is used to regulate their vertical position • Single Loop Blood Circulation-Blood goes to the gills, is oxygenated and sent to all parts of the body

11. Gills • Made of gill filaments where gases enter and leave the blood (Oxygen and Carbon Dioxide) • Gill slit-opening at the rear of the cheek • Countercurrent flow - the water passing over the gills and the blood flow inside the gills is in the opposite directions-this increases the gill’s efficiency • Fish can extract 85 % of the oxygen passing over the gills

12. Circulation of Blood in Fish • Single loop circulation in fish • Atrium-chamber with thin, muscular walls • Ventricle-a thick walled pump with much force

13. Excretory Organ-Kidneys • Kidneys are organs made up of thousands of nephrons • Nephrons are tubelike units that regulate salt and water balance and remove metabolic wastes from the blood

14. Reproduction in Fish • Separate sexes in most fishes • Usually external fertilization • Yolk sac in egg contains nutrients • Large numbers of eggs are fertilized during spawning • Sharks, Skates and Rays fertilization is internal-most are born live • Some sharks lay eggs

15. Adaptations of Fishes • Scales limit chemical exchanges through the skin; exchanges occur through the membranes of the gills • Lateral line system consists of a row of sensory structures that run the length of the body and connected by nerves to the brain; detectsvibrations

16. Agnatha “jawless” • Examples:Lampreys and hagfish live in the ocean • Lampreys attach to fish-parasites • No lateral line system • Have “round mouths”- no scales • Have Notochord, a cartilaginous skeleton, and unpaired fins

17. Hagfish • Bottom dwellers in cold marine waters • Scavengers of dead and dying fish on ocean bottom • When not feeding they remain hidden in burrows on the ocean floor

18. Chondrichthyes • CHONDRICHTHYES-SHARKES, SKATES AND RAYS • chrondros=cartilage ichthyes=fish • movable jaws • no swim bladder • cartilage strengthened by calcium carbonate or bone • placoid scales • Teeth-modified scales

19. Sharks • Sharks are scavengers • The shark’s mouth has 6 to 20 rows of backward-pointing teeth • They can detect blood from an injured animal as far as 500 miles away • They swim with a side-to-side motion of their asymmetric tail fins. • Gas exchange requires a continuous passage of water over a shark’s gills

20. Osteichthyes • Osteon=bone ichthyes=fish • Skeletons rigid, calcium bases • Movable jaws • Gill cover or operculum • Scales • Most have swim bladders • Most have separate sexes-fertilization external

21. Types of Osteichthyes or Bony Fish • The Lungfish resembles a short-bodied eel- Lungfishes have gills where gas exchange normally takes place • During dry periods they burrow unto the mud and cover themselves in mucus to stay moist until the pond refills • Their "lung" is a modified swim bladder, which also absorbs oxygen and removes wastes during this dry time • The various species are found in the lakes and rivers of South America, Africa and Australia

22. Osteichthyes Continued 2. Lobe-finned fishes-have paddle like fins with fleshy bases. 3. Ray-finned fishes have fins that are supported by the long bones called rays-Most familiar fishes and include snake-like eels, salmon, trout, bass, herring, and lantern fish (most fish we eat)

23. Morphology of a Bony Fish or Osteichthyes External Anatomy • Distinct head, trunk, and tail regions • Each side of head is operculum- Hard plate that opens at rear and covers and protects gills • Strong muscles along dorsal backbone thrust tail from side to side

24. Fin Characteristics • Thin fan-shaped membranes • Richly supplied with blood • By raising and lowering fins, regulate body temperature • Supported by rays or spines • Rays- bony yet flexible • Spines- bony and rigid

25. Scales • Skin covered with scales-highly modified bone that grow from pockets of skin • Overlap like roof shingles, all pointing toward tail to minimize friction • Grow during entire life of fish • Scales grow quickly when food is abundant and slowly when scarce • Skin contains pigmented chromatophores-which createvarious color patterns

26. Circulatory System • Adapted for rapid swimming and other high-performance activities • Consists of: Two-chambered heart • Atrium- collecting chambers • Ventricle- pumping chambers • Blood vessels • Blood-red and white blood cells • Heart pumps blood to arteriescapillaries in gills blood picks up oxygen gas and releases carbon dioxide into water blood moves to body tissues, where nutrients and wastes are exchanged blood returns by veins to heart

27. Respiratory and Excretory Systems Work Together • Gills adapted for gas exchange • Each has double row of thin projections called gill filaments richly supplied with capillaries • Large surface area allows rapid gas exchange • Gills also excrete nitrogenous wastes from body, but task carried out primarily by kidneys • Kidney’s filter out dissolved chemical wastes from blood