Trends in Animal Evolution

Trends in Animal Evolution - are 10 more efficient at...

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Trends in Animal Evolution Within the animal kingdom several evolutionary trends and advancements are seen. Note that not all animal groups have all of the organs and organ systems found in the "higher animals", a fact consistent with stepwise evolutionary history . Nor will their body plans necessarily conform to ours. Body Plans Most animals have a body plan best described as a "tube-within-a-tube" . This plan calls for two openings: one for food to enter the body (mouth), one for wastes to leave the body ( anus ). The tube-within-a-tube plan allows specialization of parts along the tube, such as a stomach, intestine, etc. The sac-like body plan has only one opening for both food intake and waste removal. Sac-like body plan animals do not have tissue specialization or development of organs. Animals with the "tube-within-a-tube" plan
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Unformatted text preview: are 10% more efficient at digesting and absorbing their food than animals with the sac-like body plan. Triploblasty: Three Tissue Layers Many, but not all, animals produce three embryonic tissue tissue layers (shown in Table 1) as they develop: the endoderm , mesoderm , and ectoderm . Some animals, most notably sponges, lack these tissue layers. Cnidarians (a group including coral and jellyfish) have only two of these layers, and are termed diploblastic. Flatworms, ribbon worms, humans, etc. have all three tissue layers, and are triploblastic. Table 1. Animal embryonic tissue layers. Tissue layer Adult tissues arising from this embryonic tissues endoderm digestion and respiration structures mesoderm muscles, bones, blood, skin, and reproductive organs ectoderm skin, brain, and nervous system...
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