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: 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 Cephalochordata Lancelets Vertebrata (Craniata) – has a well-developed head Tunicates

Divisions of the Phylum Chordata Agnatha- vertebrates lacking jaws Hagfishes and lampreys Gnathostomata- Vertebrates having jaws All other vertebrates Two forms Pisces- jawed vertebrates with appendages Tetrapoda- jawed vertebrates with appendages in the form of limbs Amniota- vertebrates whose embryos develop within a fluid-filled sac 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