23. chordates

Chordates

Chapter 23

Phylum Chordata

Phylum Chordata

Phylum Chordata

Chordates have:Bilateral symmetryA coelom Deuterostome development

Radial, indeterminate cleavageEnterocoelous coelom development

MetamerismCephalization.

Phylum Chordata

Five distinctive characteristics define the chordates:NotochordDorsal tubular nerve cordPharyngeal pouches (gill slits)EndostylePostanal tail

Notochord

The notochord is a flexible, rod-like structure derived from mesoderm.

Dorsal Tubular Nerve Cord

In chordates, the nerve cord is dorsal to the alimentary canal and is a tube.

Pharyngeal Pouches and Slits

Pharyngeal slits are openings that lead from the pharyngeal cavity to the outside.

Endostyle or Thyroid Gland

The endostyle in the pharyngeal floor, secretes mucus that traps food particles.

Postanal Tail

The postanal tail provides motility in larval tunicates and amphioxus.

Phylum Chordata

Two protochordate subphylaSubphylum UrochordataSubphylum Cephalochordata

Subphylum Urochordata

Tunicates

Subphylum Urochordata

Life Cycle of ascidian

Subphylum Urochordata

Adult of Ciona

Subphylum Urochordata

Subphylum Urochordata

Subphylum Cephalochordata

Subphylum Cephalochordata

Subphylum Vertebrata

Subphylum Vertebrata

Subphylum Vertebrata = Craniata

Neural Crest Cells

Notochord

(a) The neural crest consists of bilateral bands of cells near the margins of the embryonic folds that form the neural tube.

(b) Neural crest cells migrate todistant sites in the embryo.

Migrating neuralcrest cells

Ectoderm

Ectoderm

Dorsal edgesof neural plate

Neuralcrest

Neuraltube

The Origin of Vertebrates

The Earliest Vertebrates

Ammocoete Larva of Lampreys

Closely resembles the amphioxus lancelet

The Earliest Vertebrates

The Earliest Vertebrates

The Earliest Vertebrates

Agnathans.

Gnathostomes