Transcript Document
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. 2. 3. 4. Notochord Pharyngeal pouches Postanal tail 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 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…