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Lecture 16

Lecture 16 - Echinoderms and Chordates.docx

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McGill University
Biology (Sci)
BIOL 111
Suzanne Gray

October 27 Echinoderms and Chordates Protosomes vs. Deuterostomes:  The two major evolutionary lineages of Bilateria  Split around the Cambrian period (~500 mya)  Stome = mouth  Differences in embryonic development o Protosomes: the mouth develops first o Deuterostomes: the anus develops first o Both are Bilaterians (triploblastic) Animal Evolution thus far:  Multi-cellularity  Tissues  Gut  Mesoderm  Head  Segmentation  Nervous System  Anus  Circulatory System  Hard Skeleton  Coelom In Protostomes:  Central nervous system is ventral  Anus is from the 2ndopening  Circulatory system has a dorsal heart  Hard skeleton is iexternal  Coelom develops from work  how to make a coelom o Schizocoely: splitting within the mesoderm, protostomes  Buds of mesoderm split in the middle, ending up with the coelom  Spiral Cleavage: at an angle  is seen in some lophotrochozoans (spirilians) In Deuterstomes:  Central nervous system is dorsal  Anus is from the 1 opening  Circulatory system has a ventral heart  Hard skeleton is internal  Coelom develops from  how to make a coelom o Enterocoely: mesoderm forms pockets from gut o Radial cleavage: one on top of another  the ancestral condition for animals October 27h Echinoderms and Chordates Who are the Deuterostomes:  Echinoderms  Chordates: Urochordates, Cephaochordates, Vertebrates Deuterostomes  Echinoderms:  “Spiny skin”  ~ 7,000 extant species  Strictly marine  Benthic (bottom dwellers)  Diverse modes of nutrition  Example: sea stars, sea urchins, sand dollars Endoskeleton:  Hard  Composed of CaCO pla3es  Continuous growth o Plates enlarge and new ones are added  Covered by thin layers of skin and muscle Symmetry and Body Plan:  Penta-radial symmetry: 5-part symmetry  Bilateral symmetry: evolved from bilaterally symmetrical ancestors  Body Plan: anterior-posterior foreshortening o Flopped over, mouth down o Internal structures also are arranged pentaradially o A water vascular system is unique to echinoderms o Squeeze the ampulla will extend water, which can be used for locomotion o Madrepoint is where the water enters  System of water-filled tubes  End in “tube feet” (podia)  Extend through pores of endoskeleton  Used for locomotion, feeding, respiration, excretion  Sensory structures (chemical, tactile)  Anus on the aboral surface  Mouth on the oral surface What group has an aboral surface? Cnidarians Describe echinoderms nervous system? Radial nerves and sensory nerves in the tube feet Asexual Reproduction: fragmentation, which leads to regeneration Arm may be dropped and regenerated to: 1) Escape predation 2) Decrease chance of infection Oc
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