Classification
Characteristics biologists use when classifying organisms
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| forms skin and nervous system | ||
| forms viscera and digestive system | ||
| forms blood and bones | ||
| primitive animals lacking a mesoderm | ||
| advanced animals with all three germ layers | ||
| a fluid-filled body cavity, lined with mesoderm tissue, provides space for elaborate organ systems | ||
| triploblastic with solid bodies, no cavity between digestive tract and outer body wall; includes platyhelminthes | ||
| body cavity is only partly lined with mesoderm tissue; includes nematodes (round worms) | ||
| has a true coelom (primitive); first opening = mouth, second = anus; includes annelids, mollusks, and arthropods | ||
| has a true coelom (advanced); first opening = anus, second = mouth; includes chordates and echinoderms | ||
| no true tissues; sessile; filter nutrients from water; choanoctyes, spicules act as skeleton, amoebocytes | ||
| radial symmetry, body plan is either polyp (hydra) or medusa (jelly fish), diploblastic (no mesoderm, mesoglea only), gastrovascular cavity, all have stinging cells (cnidocytes) that contain stingers called nematocysts; includes hydra, jelly fish, coral, sea anemones | ||
| protostome, acoelomate (triploblastic with bilateral symmetry), have an anterior and posterior with sensory apparatus eyespots at head end, extremely flat body, most are parasitic | ||
| bilateral symmetry, pseudocoelom transports nutrients and body fluids, lacks a circulatory system, pseudocoelom acts as a hydrostatic skeleton, many are parasitic | ||
| protostome coelomates, nephridia remove urea, closed circulatory system (heart consists of 5 pairs of aortic arches), diffusion of respiratory gases through skin, blood carried hemoglobin and oxygen, hermaphrodites with no self-fertilization | ||
| protostome coelomates, soft body often protected by shell, bilateral symmetry with head-foot, visceral mass, and mantle, radula (tooth-bearing structure that acts like a tongue), open circulatory system with blood-filled spaces called hemocoels, most have gills and nephridia | ||
| protostome coelomates, jointed appendages, segmented with head, thorax, and abdomen, chitinous skeleton, open circulatory system with tubular heart and hemocoels, malpighian tubules for removal of uric acid, trachea | ||
| deuterostome coelomates, most are sessile, bilateral symmetry as embryo, radial as adult, reproduces by fragmentation and regeneration, endoskeleton grows with animal (does not have to be replaced) | ||
| dueterostome coelomates, have a notochord | ||
| mothers nourish babies, homeotherms | ||
| young develop interally in a uterus connected to mother by a placenta | ||
| completes development in a pouch attached to mother (kangaroos) | ||
| egg laying mammals (platypus) | ||
| dexterous hands with opposable thumbs, front facing eyes set close together, nurture young for a long time, nails replace claws | ||
| Animalia, Chordata, Mammalia, Primates, Hominidae, Homo, sapiens |