LIFESCI 1 Lecture Notes - Lecture 21: Chondrichthyes, Elasmobranchii, Arthropod
Document Summary
Skeletons: animal skeletons meet at joints (transmit muscle forces for movement and body support, 3 types of skeletal systems: hydrostatic, endoskeleton, and exoskeleton. Hydrostatic: evolved early in multicellular animals (first cnidarians = jellyfish and anemone) = 600 million years ago: found in nearly all multicellular animals and vascular plants. Fluid in body cavity acted as support. Muscles exert pressure against fluid to produce movement: 2 sets of muscles surround fluid = controls width/length of body cavity or whole animal. Circular muscles = diameter of body cavity. Longitudinal muscles = length: sea anemone = bends body in different directions to feed/resist water currents. Close mouth = keep fluid volume constant. Can extend into water column by contracting circular muscles and relaxing their longitudinal muscles: controlling fluid = adjust shape. Contract longitudinal muscles to allow water to escape from body cavity (when threatened, these muscles are retracted: also earthworms move hydrostatic segments along the body.
