Chordates and Fishes

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Chordates and Fishes
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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

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• 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

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Classification

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

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

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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

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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)

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Vertebrate Classes

• Fish
• Amphibians
• Reptiles
• Birds
• Mammals

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• 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

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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

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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 gills
  efficiency
• Fish can extract 85 of the oxygen passing over
  the gills

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Circulation of Blood in Fish

• Single loop circulation in fish
• Atrium-chamber with thin, muscular walls
• Ventricle-a thick walled pump with much force

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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

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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

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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 detects
  vibrations

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Agnatha jawless

• ExamplesLampreys 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

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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

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Chondrichthyes

• CHONDRICHTHYES-SHARKES, SKATES AND RAYS
• chrondroscartilage ichthyesfish
• movable jaws
• no swim bladder
• cartilage strengthened by calcium carbonate or
  bone
• placoid scales
• Teeth-modified scales

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Sharks

• Sharks are scavengers
• The sharks 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 sharks gills

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Osteichthyes

• Osteonbone ichthyesfish
• Skeletons rigid, calcium bases
• Movable jaws
• Gill cover or operculum
• Scales
• Most have swim bladders
• Most have separate sexes-fertilization external

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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

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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)

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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

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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

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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
• create various color patterns

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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

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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
• Kidneys filter out dissolved chemical wastes
  from blood

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