PHYLUM CHORDATES
Characteristics

Characteristics similar to other phylum discussed:
 Bilateral
symmetry
 Triploblastic
 Well-developed coelom
 Metameric- Segmented body
 “tube within a tube” arrangement
 Cephalization
Characteristics

Deuterostome
 Radial
clevage
 Anus forms first
 Primitively Enterocoelous
 Early
chordates were known to be enterocoelous, however,
due to the large yolk of modern species, most vertebrates
are schizocoelus
Characteristics

5 distinctive characteristics that set chordates apart
from all other phyla:
1.
2.
3.
4.
5.
Notocord
Dorsal tubular nerve cord
Pharyngeal pouches or slits
Endostyle
Postanal tail
1. Notocord

All members of this phylum contain a
notochord (noton, back + chorda, cord)
 Can
be restricted to early development or may
be present throughout life
 Rod like, semi rigid body of cells enclosed by a
fibrous sheath, which extends the length of the
body just ventral to the central nervous system.
 Primary purpose is to stiffen the body,
providing skeletal scaffolding for the
attachment of swimming muscles
2. Dorsal Tubular Nerve Cord



Solid, single nerve cord is dorsal to the alimentary
canal and is a tube
Hollow center
Anterior end becomes enlarged to form the brain
3. Pharyngeal Pouches and Slits


Slit openings
Give rise to several structures:
 Middle
ear cavity
 Tonsils
 Parathyroid
glands
 Eustachian tube (equalizes pressure between ear and
nasal canal, surrounding ear drum)
 Gills
4. Endostyle or Thyroid Gland

Endostyle- secretes mucus that traps small food
particles
 Work
together with hormone secretion
5. Postanal Tail



End of the notochord (stiffened)
Used primitively for swimming
Humans have evidence of the tail but evidently it is
vestigal (the coccyx, tail bone)
Divisions of the Phylum Chordata

Protochordata (Acraniata)- lack a well-developed
head
 Subphylum
Urochordata
 Tunicates
 Subphylum
 Lancelets

Cephalochordata
Tunicates
Vertebrata (Craniata) – has a well-developed head
Divisions of the Phylum Chordata

Agnatha- vertebrates lacking jaws


Hagfishes and lampreys
Gnathostomata- Vertebrates having jaws

All other vertebrates

Two forms



Amniota- vertebrates whose embryos develop within a
fluid-filled sac


Pisces- jawed vertebrates with appendages
Tetrapoda- jawed vertebrates with appendages in the form of limbs
Reptiles, birds, mammals
Anamniota- vertebrates lacking this adaptation

Fishes and amphibians
PHYLUM CHORDATES
EVOLUTION
Subphylums

There are 3 subphylum belonging to the phylum
Chordata

Remember we have already discussed two:

Protochordata (lack a well-developed head)
 Subphylum
Urochordata (tunicates)
 Subphylum Cephalochordata (lancelets)
Further Divisions

Subphylum Vertebrata (have a well-developed head)
 Super


class Agnatha (lack Jaws)
Class Myxini (hagfish)
Class Petremyzontida (lampreys)
 Super
Class Gnathostomata (have jaws)
 Pisces (Jaws with appendages)


Class Chondrichthyes (cartilaginous fishes)
Osteichthyes (boney fishes)
 Class Actinopterygii (ray-finned fishes)
 Class Sacropterygii (lobe-finned fishes)
 Tetrapoda (Jaws with appendages as limbs)




Class Amphibia
Class Reptilia
Class Aves
Class Mammalia
New Evolutionary Tree

Must include when the following traits emerged:
Protochordata
 Vertebrata
 Agnatha
 Gnathostomata
 Pisces
 Tetrapoda

Use pg 499 in your text book as a reference
 Also include the Phylum Echinodermata



Use front cover and pg 473
Save room for Subclasses, Orders and Suborders