Class Chondrichthyes




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Class Chondrichthyes
General Overview

  • Cartiligenous fishes

  • Three subclasses

    • Sharks (elasmobranchi)

    • Skates & Rays (elasmobranchi)

    • Chimaeras


Habitat

  • Water Habitat

  • Primarily salt water (oceans)

    • Reefs (common)

    • Coastal Areas (common)

    • Estuaries

    • Open ocean (not as common)

    • Muddy/sandy bottom (primarily skates & rays)

    • Deep ocean (primarily chimaeras)

  • Freshwater (rare)


Feeding Mechanisms

  • Most sharks have large jaws that help them actively hunt prey

    • Teeth often give a clue as to what they eat

    • Jaws can detach from the skull, allowing for larger bites

    • Hundreds of teeth are arranged in rows, constantly replacing old teeth

  • Rays have a flattened and flexible snout

    • Snout allows them to grub for food

    • Teeth are plates that are designed to crush food such as mollusks

  • Some are filter feeders

  • Well developed sensory organs help locate prey

    • Olfactory

    • Electroreception

      • Lateral line

    • Eyesight



Reproduction

  • Sexual

  • Males (including sharks, rays, chimaeras) have claspers that hold him in place during mating

    • Males can be very aggressive, surrounding a female and preventing her escape

    • Males will often bite during courtship

  • Females

    • Have two uteruses

    • Female rays have been known to store sperm until conditions are favorable for bearing young

    • Pregnant females have been known to migrate to more favorable areas for young

    • Rarely, mothers will protect young for a shortened period of time

  • Young

    • Are miniature adults - there is no larval stage

    • Eggs

      • Tough, leathery, attached to substrate

    • Live birth

      • Litters are of a small size

      • Pups fight within the womb; only the strongest is born

      • No placental - only a yolk

        • When yolk is depleted, mother supplies nutrition


Unique Characteristics

  • Senses are very well developed

    • Olfactory senses

    • Inner ear

      • Provides balance

      • Also allows hearing underwater

    • Electroreception

      • Ampulae of Lorenzini

      • Lateral line

    • Touch + taste

      • “Bite & Spit” theory

  • Skin is covered in tiny scale-like structures called denticles (feels like sandpaper!)

  • Gas exchange occurs at the gills for sharks

  • Skates and rays have spiracles in addition to gills


Sharks

  • Not all sharks are of the classic fusiform shape

    • Wobbegong

  • Today sharks are threatened by overfishing as a result of sport, fear (“Jaws”), and food

  • The sharkfin business is destroying shark populations - the fins are cut off and the animal is thrown back into the ocean to die


Skates & Rays

  • Body is flattened, with enlarged pectoral fins forming a disc

  • The jaw is also flattened, often with fused teeth that are better suited to crushing and grinding

  • Also has filter feeders: manta ray

  • Spiracles

  • Males also have claspers

  • Stinging spine

  • Some rays house electrical organs


Chimaeras

  • Primitive group, poorly understood

  • Taxonomy is debated

  • Consists of ratfishes, rabbitfishes, and elephantfishes

  • Live at extreme depths

  • Feed on mollusks and other invertebrates

  • Large pectoral fins to help them glide, large eyes, long whiplike tail

  • Dorsal fin occasionally features a poisonous spine, depending on the species


Sources

  • Book: “The Nature Company Guides: Sharks & Rays” by multiple authors: Tricas, Deacon, Last, McCosker, Walker, Taylor

  • Book: “Smithsonian Institution: Animal” Edited by David Burnie & Don E. Wilson

  • Wikipedia: http://en.wikipedia.org/wiki/Holocephali

  • Wikipedia: http://en.wikipedia.org/wiki/Chondrichthyes

  • Seaworld.org: http://www.seaworld.org/animal-info/info-books/sharks-&-rays/anatomy.htm


DONE


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