BIOL 202 Lecture Notes - Lecture 13: Haemal Arch, Dorsal Nerve Cord, Dermal Bone
24 Feb 2016
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Early fish, sharks & rays lecture 2. Endoskeleton with skull surrounding brain (sophisticated neural tube) Locomotion & buoyancy: streamlined, light skeleton, red/white myomeres, swim bladder, tail propulsion. Sense organs: moveable lens (light reception poor, keen olfaction, inner ear (sound important, lateral line electroreceptors. Gas exchange: counter-current gills habitable, virtually all early vertebrates were fish, early environment mostly aquatic before sufficient terrestrial environment was, 3 major features. Cartilage (ancient: hard but flexible, entire skeleton or portions, elastic fibres not seen in bone, chondrocytes within lacunae surrounded by matrix. Excretion & water balance (salts: gills, posterior kidney. Ancestral: hard, rigid, support, protection, lever system for muscles action, osteocyte cells within lacunae, matrix of capo4 and caco3, dermal bone: 2d membrane near body surface, endochondral bone: 3d formed in cartilage, origins. Conodonts (clydagnathus) worm like creature with tail, denticles like teeth, paired eyes. Ostracoderms arose in ocean, but radiated widely into freshwater by silurian/devonian.
