Introduction to Chordates Chapter 15

Basics Bilateral symmetry Segmented body Three germ layers Well-developed Coelom Endoskeleton Complete digestive system Closed circulatory system

Chordate Characters 1.Notochord 2.Pharyngeal pouches 3.Postanal tail 4.Nerve cord (dorsal)

Notochord Flexible rod-like structure First part of endoskeleton (in embryo) Axis for muscle attachment In most verts, its replaced by vertebrae

Pharyngeal pouches Pharyngeal slits: vary in degree and function –Aquatic chordates: leads to outside of cavity –Amniotes: forms only groves –Fish: became gills

Postanal tail Tail and musculature provide motility –Fish: highly evolved –Other groups: become vestigial

Nerve cord Dorsal to alimentary canal Tubular Brain on anterior end Formed from ectoderm

SP: Urochordata Tunicates

SP: Urochordata Tunicates Found at all ocean depths –Largely sessile Larval forms have all chordate features –Adults loose many of these Notochord and tail disappear Dorsal nerve cord is reduced Tunic (test): protective covering around animal

Adult Tunicates

Adult and Tadpole Larva of Urochordate

SP: Urochordata Example Ascidians: sea squirts –More common intertidal animals –Can be found attached to rocks –Colonial and solitary forms Feeding –Filter feed with mucus net

SP: Cephalochordata Lancelets Marine Found in sediments near costal waters Feeding –Filter feed with mucus net

Lancelet Amphioxus

SP: Cephalochordata Bauplan Long slender, translucent Has four chordate characters Is though to be living descendant of ancestor that gave rise to vertebrates

SP: Vertebrata AKA Craniata: all groups have a cranium –braincase Thought to be monopyletic Share other important characteristics

SP: Vertebrata Fossil invertebrate chordates are rare and known primarily from two fossil beds. Pikaia from Cambrian Burgess Shale

Haidouella 530 MYO China

The Early Vertebrates Ostracoderms- Armed Jawless Fishes 505 MYO

SP: Vertebrata Living Endoskeleton Efficient Respiration (Pharynx) Advanced Nervous System Paired limbs

Living Endoskeleton Grows with body –No molting –Efficient use of materials Muscle attachment Protect body and body protects it Made from –Bone –Cartilage

Efficient Respiration (Pharynx) Pharynx is result of shift from filter feeding Increased metabolic rate –Addition of capillaries –Muscular aortic arches

Advanced Nervous System Predation favored more complex nervous system –Eyes with lenses –Paired eyes Two innovative adaptations –Neural crest-forms cranium –Specialized Sense Organs- nose, eyes, ears….

Paired limbs Pectoral and pelvic appendages –Swimming stabilizers Jointed limbs –Work well in terrestrial environments

The Big Picture Four major evolutionary events binds the chordates into a group –Many of these allowed chordates to be successful on land Urochordates as adults appear to be sponges or cnidarins, but as larvae they have all structures shared by chordate Remember what it means to be a vertebrate…