Phylum Chordata 4/12/07 HW: Study These Notes.. General characteristics 1. bilaterally symmetrical, deutersostomate animals deuterostome – an animal whose.
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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.
General characteristics, cont’d
4 unique characteristics present at some stage in development: Notochord Pharyngeal Slits Dorsal Tubular Nerve Cord Postanal Tail
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.
Pharyngeal Slits
Pharyngeal Slits: a series of openings in the pharyngeal
region between the digestive tract and the outside of the body
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
Examples of Chordates
1. sea squints (or tunicates)2. amphioxus3. lampreys4. hagfish5. sharks, rays, skates6. bony fishes7. frogs, toads, salamanders8. alligators, snakes, lizards9. birds10. mammals
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
Habitat
Worldwide distribution, from the temperate to the subpolar regions, from the shallow waters of the seashore to depths of 100 fathoms (600 feet)
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
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)
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.
Adaptations, Cont’d
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!
That’s why they eat so much!!
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