Sharks, Skates, Rays and Chimeras

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Sharks, Skates, Rays and Chimeras
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Class Chondrichthyes

• Subclass Elasmobranchii
• Sharks
• Skates and Rays
• Subclass Holocephali
• Chimaeras (Ratfish)
• Traits
• Habitats

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Adaptations

• Buoyancy
• Respiration
• External covering
• Feeding
• Movement
• Sensory systems

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Buoyancy

• Huge oil-filled liver
• A shark that has an air weight of 1,000 kg.
  weighs only 3.3kg in water
• Lift created by a heterocercal tail

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Caudal Fin Types

• Heterocercal

• Homocercal

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Respiration

• Chondrichthyes employ 3 different methods of
  respiration
• Two pump method

• Ram ventilation

• Spiracles

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External Covering

• All Chondrichthyes have placoid scales in one
  form or another
• Placoid scale modifications
• Spine of stingray, dorsal spine of dogfish,
  defensive spines in the skate, and teeth

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Scale Types
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Feeding

• Most are specialized predators and have
  dentition that reflects their lifestyle
• Sharks that prey on fish and marine mammals have
  triangular blade-like teeth
• Used for grabbing and tearing
• Can exert biting pressures of 2,800 kg/cm3
• Teeth are constantly being shed and replaced
• Up to 30,000 in a lifetime

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Feeding

• Digestion
• Spiral valve

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Movement

• Pelagic sharks have rete mirabile

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Sensory Systems

• Elasmobranchs a have well-developed sensory
  system which acts in concert to locate prey and
  find their way around the environment
• Some species can detect a drop of blood as
  dilute as 1 part per billion
• Also, very good at following an odor trail

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Sensory Systems

• Hearing
• Olfaction
• Lateral line

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Sensory Systems

• Visual systems are well developed for use during
  night and day
• Tapetum lucidum increased vision at night
• Nictitating membrane

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Sensory Systems

• Ampullae of Lorenzini

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Chondrichthyes Reproduction

• Most species have extended gestation periods in
  egg cases or in the body cavities of females
• Young traits

• Internal fertilization, through the use of
  claspers on the male

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Chondrichthyes Reproduction

• Oviparity
• Viviparity
• Yolk-sac Viviparity
• Uterine Viviparity
• Cannibal Viviparity
• Placental Viviparity

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Oviparity - Egg Laying

• Oviparity

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Viviparity

• Yolk-sac Viviparity (Ovoviviparity)
• Eggs are produced and retained inside the mother
• Shell disappears and young are retained until
  fully developed
• Uterine Viviparity
• Mother secretes nutrient rich fluid which is
  taken up through the skin of the embryo

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Cannibal Viviparity

• Young in each oviduct consume unfertilized eggs
  or other siblings

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Placental Viviparity

• Nutrients are supplied to the embryo directly
  from the mother via a umbilical cord

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Chondrichthyes Life History

• Strategy of Elasmobranchs
• Produce precocial young with high survival rates
• Slow growing, long lived, and reach sexual
  maturity at a late age
• This reproductive strategy is why elasmobranchs
  can not sustain an intensive fishery

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Class Chondrichthyes

• Subclass Holocephali
• Possess cartilaginous skeleton, intromittent
  organs, spiral valve intestine, and oil filled
  liver
• As a group found mostly between 80-2,600 meters,
  feeding on hard shelled invertebrates