Phylum Chordata

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Phylum Chordata

• 4/12/07
• HW Study These Notes.

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General characteristics

• 1. bilaterally symmetrical, deutersostomate
  animals
• deuterostome an animal whose mouth develops
  from cells other than those at the opening of the
  gastrula.

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General characteristics, contd

• 4 unique characteristics present at some stage in
  development
• Notochord
• Pharyngeal Slits
• Dorsal Tubular Nerve Cord
• Postanal Tail

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Notochord

• The notochord is
• a supportive rod that extends most of the length
  of the animal dorsal to the body cavity and into
  the tail

Notochord on developing zebrafish.
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Pharyngeal Slits

• Pharyngeal Slits
• a series of openings in the pharyngeal region
  between the digestive tract and the outside of
  the body

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Dorsal Tubular Nerve Cord

• Dorsal Tubular Nerve Cord
• runs along the longitudinal axis of the body,
  just dorsal to the notochord, and usually extends
  anteriorly as a brain

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Postanal Tail

• The postanal tail
• extends posteriorly beyond the anal opening

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Examples of Chordates

• sea squints (or tunicates)
• amphioxus
• lampreys
• hagfish
• sharks, rays, skates
• bony fishes
• frogs, toads, salamanders
• alligators, snakes, lizards
• birds
• mammals

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Dogfish Shark

• The representative member of the phylum Chordata
  we will begin with is the spiny dogfish shark,
  Squalus acanthias.
• phylum Chordata (having general characteristics
  listed above)
• ? subphylum Vertebrata (having backbone)
• ? class Chondrichthyes (skeleton made of
  cartilage)
• ? subclass Elasmobranchii
• The spiny dogfish shark, Squalus acanthias.
• a.k.a piked dogfish, skittledog, spotted dogfish,
  white-spotted dogfish, codshark, and thorndog

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Dogfish Anatomy
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Habitat

• Worldwide distribution, from the temperate to
  the subpolar regions, from the shallow waters of
  the seashore to depths of 100 fathoms (600 feet)

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Niche

• They are voracious eaters, feeding on
• fish
• Crustaceans
• Squid
• Gastropods
• jelly fish
• even red and brown algae.
• omnivorous devouring both plant and animal
  matter

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Life Span

• Typically from 25-30 years.

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Reproduction

• Internal fertilization most shark pups hatch
  internally, and continue their development within
  the uterus of the mother
• Ovoviviparous born alive as much smaller
  versions of the adult
• Gestation period up to 2 years (the longest of
  any vertebrate)

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Adaptations

• Sharks do not drink water?! The regulate their
  osmotic pressure by retaining a high
  concentration of urea and other solutes in their
  body fluids. Water enters their cells by
  osmosis.

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Adaptations, Contd

• The lack a swim bladder as seen in most bony
  fish.
• The above 2 facts are responsible for the
  following interesting fact. Sharks must keep
  moving in order to survive. If they stop moving
  they sink because they are somewhat heavier than
  the water they displace. If stopped, they sink,
  and will be crushed by the water pressure of the
  deep ocean. Sharks of the deeper ocean must
  continue to move from the moment of birth to the
  moment of death!
• Thats why they eat so much!!