Prechordates {stem chordate} had notochord in both larval and adult stages, allowing muscle attachment, providing long body axis, and affecting reproduction.
germ layers
Prechordate embryos had three cell layers. Endoderm is inner tube, mesoderm is between, and ectoderm is outer tube. Ectoderm becomes senses, nerves, and outer skin. Mesoderm becomes muscles and glands. Endoderm becomes digestive tract.
coelom
Prechordates had tube-shaped body structures, with digestive tube inside main tube.
deuterostome
During development, inner tube opens to outside anus first.
head and tail
Having coelom makes longitudinal bodies, from which head, trunk, and tail can separately evolve. Head holds central ganglia and mouth.
bilateral symmetry
Body parts and appendages have pairs, one right and one left. Body also has front and back. Bilateral symmetry [-590000000] resulted from having coeloms.
segmentation
Prechordates had repeated body structures, allowing different lengths and requiring coordination among body segments. Segments can vary independently.
development stages
Prechordates had streamlined larvae with cilia for swimming in mobile stage. Adult sessile stage did not move. Prechordate ciliated larvae evolved to become stem chordates.
bone
Stem chordates calcified tissue to make bone, allowing better muscle attachment, more shapes, and more textures.
respiration
Stem chordates had external respiration by gills, allowing efficient oxygen uptake and carbon-dioxide removal from blood. Body-side gill slit openings allowed water to flow into mouth and through gills, resulting in better respiration.
nervous system
Prechordates had main head ganglion, with peripheral nerves to tail. Head ganglion provided unified control for all body segments and allowed swimming, burrowing, and defense. Stem chordates had dorsal hollow nerve, so all nerves have same pathway from head to periphery. Cerebrospinal fluid was in dorsal hollow nerve. Nerves were bilateral sense and motor paths. Interneurons coordinated neurons.
hormones
Hormones from glands affect neurons and other tissues.
Biological Sciences>Zoology>Kinds>Chordate
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Date Modified: 2022.0224