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Phylum Chordata


3 Subphyla:

urochordata & cephalochorda are Invertebrate chordates (no vertebral column)

vertebrata - vertebrates. (vertebrate animals)
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4 Anatomical Features Characterize phylum chordata  (gut means intestine)
I. Notochord - A longitudinal, flexible rod located b/w the gut & nerve cord present in all chordate embryos
composed of large fluid filled cells encased in stiff fibrous tissue.

In some invert (invertebrate ) chordates & primitive verts (vertebrates)  (Lamprey) notochord persists to support the adult.

II. Dorsal Hollow Nerve Cord

Unique to chordates; invertebrates have soid, usually ventral nerve cords
-Brain & spinal cord (CNS) develops from this nerve cord.
III Pharyngeal Gill Slits
-These gill slits function
  For suspension feeding in invertebrate chordates (invertebrate chordates first function in suspension feeding *)
-They become modiied for gas exchange during evolution of vertebrates.

IV. Muscular Postanal Tail
Tail extending beyond anus.
-contains skeletal elements & muscles.
-provides propulsive force in aquatic species.
-may be prehensile (grasping) in aboreal forms (tree dwelling)
ex. - opossum, Boa constrictor.
/* Old world monkeys do not have a prehensile tail */

Invertebrate
chordates

A) Subphylum Urochordata
"Tunicates (they're cloked in a tunic kinda like an exoskeleton)" "Sea Squirts"
Entire animal cloaked in a tunic made of a cellulose like carbohydrate
-most are sessile marine animals
-some species are planktonic, others are colonial (live together).
-Tunicates are "Filter feeders"
-Adult tunicates bear little resemblance to other chordates (nothing quite like it)
-They lack a notochord, a nerve cord & tail (only the adults lack these)
-they posess ONLY pharyngeal slits.(adults only) (only chordate characteristic that they have)
*Larval Tunicates are Free Swimmers & possess all 4 chordate characteristics (Tadpole larvae)
B)Subphylum Cephalochordata
Amphioxus (outdated name - contemporary name in Branchiostoma *)
"Lancelets"
-Blade like shape
-all 4 chordate characteristics.
-chordate characteristics are prominent & persist in adult.
-Marine filter feeders
-burrow tail first into sand w/ only Anterior exposed.
-Feeble swimmers w/ fish like motions.
-Most zoologists feel vertebrate ancestors possessed all 4 chordate characteristics & were suspension feeders.
-They may have resembled lancelets but were less specialized.
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Vertebrates
Subphylum Vertebrata

(craniata)
-They retained the primitive chordate characteristics while adding other specializations.
Characteristics
    -Neural Crest - Group of embryonic cels found only in vetebrates contribute to formation of certain skeletal components & other structures.  /*The nervous system is the FIRST thing to develop */
-Pronounced cephalization (censory structures centered an anterior end )
-Vertebral column & cranium as the main axis replacing notochord as basic skeleton.
-closed circulatory system.
2 to 4 chambered heart.
-Vertebrates divided into 2 major groups (Super Classes):
A) Superclass Agnatha "jawless vertebrates"
B)Superclass Gnathostomata "Jawed Vertebrates"     /* Hagfish is exclusively marine */
Gnathostomes divided into 6 classes:
1)Chondrichthyes
2) osteichthyes - ostei(bones)thyes(cartilage)
3)Amphibia
4)Reptilia
5)Aves
6) Mammalia
Last 4 classes called
Tetrapod vertebrates:
/* snakes have hips */
(2 pairs of limbs that support it on land )
In additon to being tetrapods repties, birds, mammals are
Amniotes - Possess a shelled, h20 resistant egg that allows completion of life cycle on land
Amniotic egg A.K.A Cleidoic egg  (Reptiles - 1st vertebrates to have come on land - 1st w/ cleidoic egg ).  (Amphibians are not amniotes)
-Most mammals don't lay eggs, b ut retain other features of the AMniotic condition
therefore they are considered Amniotes.