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Chordates and Fishes. 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
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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
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
Classification Phylum Chordata has 3 subphyla • Urochordata-Tunicates • Cephalochordata-Lancelets • Vertebrata Subphylum Urochordata • Hollow barrel shaped Urochordates are commonly called Tunicates and Sea Squirts
Subphylum Cephalochordata • Marine organism (usually shallow water) • Best represented by a blade-shaped, animal called a lancelet
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
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)
Vertebrate Classes • Fish • Amphibians • Reptiles • Birds • Mammals
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
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
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
Circulation of Blood in Fish • Single loop circulation in fish • Atrium-chamber with thin, muscular walls • Ventricle-a thick walled pump with much force
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
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
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
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
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
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
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
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
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
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)
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
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
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
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 arteriescapillaries 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
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