Biology AP Evolution of Nervous System 1) Phylum Cnidarians (i.e Hydra) a) Nerve nets are spread throughout the body; they control gastrovascular cavities b) Exhibits radial symmetries 2) Phylum Echinodermata (i.e Starfish) a) Radial nerves and much more categorized b) They are much more efficient in complex movements c) Bilateral symmetries as larvae; Radial symmetries as adults 3) Phylum Platyhelminthes (i.e Flatworms) a) First organism that shows cephailziation * Cephailization = the concentration of nerve cells toward the anterior part = Found in the animal that has bilateral symmetry = Makes the animals more specialized in terms of movement = Shows evolutionary trend (increases as it goes on) b) Consist of a small eyespots and longitudinal nerve cords at the (ventral back side) 4) Phylum Annelida & Arthropoda (i.e Earthworms and insects) a) Simply contain more nerve cells b) Have ganglia and ventral nerve cords (clusters of neurons that are arranged in) 5) Phylum Chordata (i.e Vertebrates) a) Consist of a brain and ventral longitudinal nerve cords b) Cerebrospinal Fluid = The blood-derived fluid that surrounds the brain Main components = Glucose, high concentrations of sodium, chloride, and calcium ions, and low concentration of potassium ions. Main functions = to protect against infection (immunity) = to nourish and cushion the brain and spinal cord Significance = the composition of sea water is similar to this and the organisms might have come from the water and this provides enough nutrients to the humans.