Ch 23 Animals The Invertebrates

Ch 23 Animals The Invertebrates - Ch 23 Animals The...

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Ch 23 Animals The Invertebrates Characteristics of Animals - Multicelled ( Have Organs and Systems) - Most are diploid - all are heterotrophic (get Carbon and food by digesting them or by absorption) - Over 1.5 million species of animals are known, many more likely exist - There are over 35 animal phyla—all but one contain only invertebrates (no backbone) chordata , is composed mainly of vertebrates (with a backbone of bone or cartilage). - require Oxygen for Cellular respiration - reproduce both sexually and asexually - most are motile during some time in their life cycles (may move through water) - the zygote divides by mitosis giving rise to multicellular animals with 3 1 o tissues ectoderm outer tissue, mesoderm middle tissue (organs and gut) endoderm inner a. Animals with only ectoderm and endoderm (diploblastic) have the tissue level of organization. b. Animals with three tissue layers (triploblastic ) have the organ level of organization. Types of Symmetry Asymmetry means there is no particular body shape (e.g., sponge). Radial symmetry describes body parts arranged around an axis, like spokes of a wheel (e.g., starfish). Radially symmetrical animals may be sessile (i.e., attached to a substrate or less motile). This symmetry enables an animal to reach out in all directions from one center. Bilateral symmetry describes a body having a right and left, or complementary halves . i. Only one longitudinal cut down the center produces mirror halves. ii. Bilaterally symmetrical animals tend to be active and to move forward at an anterior end (top or head region). iii. The development of a head to localize the brain and sensory organs at the anterior end is called cephalization. Most have: anterior = head posterior =end dorsal = back ventral = Front Body Plans Animals with a sac plan have an incomplete digestive system with only one opening used for both entrance and exit of food. Animal with the tube-within-a-tube plan have a complete digestive system with separate entrance and exit to the digestive system; this allows specialization zones along the digestive tract.
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Type of Coelom (gut or stomach) Acoelomates lack a body cavity or coelom although they have mesoderm. Pseudocoelomates possess a body cavity that is incompletely lined by mesoderm because the cavity develops between the mesoderm and endoderm. Coelomates possess a body cavity completely lined with mesoderm; coelomates are either protostomes or deuterostomes . (fig: 23.4 A-C) Protostomes have an embryonic development where the first embryonic opening (blastopore) becomes the mouth. Deuterostomes develop with the blastopore becoming the anus. Segmentation is repetition of body parts along the length of the body. The repeating segments may or may not be similar to each other. a.
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Ch 23 Animals The Invertebrates - Ch 23 Animals The...

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