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  3. The opposite of adaptive divergence is an interesting and fairly common expression of evolution. Whereas related groups of organ

The opposite of adaptive divergence is an interesting and fairly common expression of evolution. Whereas related groups of organ

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问题     The opposite of adaptive divergence is an interesting and fairly common expression of evolution. Whereas related groups of organisms take on widely different characters in becoming adapted to unlike environments in the case of adaptive divergence. We find that Unrelated groups of organisms exhibit adaptive convergence when they spot similar modes of life or become suited for special sorts of environments.  For example, invertebrate marine animals living firmly attached to the sea bottom or to some foreign object tend to develop a sub- cylindrical or conical form. This is illustrated by coral individuals, by many sponges, and even by the diminutive tubes of bryozoans. Adaptive convergence in taking this coral-like form is shown by some brachiopods and pelecypods that grew in fixed position. More readily appreciated is the streamlined fitness of most fishes for moving swiftly through water; they have no neck, the contour of the body is smoothly curved so as to give minimum resistance, and the chief propelling organ is a powerful tail fin. The fact that some fossil reptiles (ichthyosaurs) and modem mammals (whales, dolphins) are wholly fishlike in form is an expression of adaptive convergence, for these air-breathing reptiles and mammals, which are highly efficient swimmers, are not closely related to fishes.  Unrelated or distantly related organisms that develop similarity of form are sometimes designated as homeomorphs (having same form).  
Invertebrate marine animals are ______.
选项 A、homeomorphs
B、conical in form
C、coral
D、without bones
答案D
解析 无脊椎的海底动物没有骨头。作者在文中说，无脊椎海底动物牢牢地依附于海底或依附于某种异物上，这说明无脊椎海底动物没有骨头。
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