A subclass of marine mollusks that includes limpets and abalones, characterized by simple gill structures arranged in a shield-like pattern.
From Greek 'aspis' (shield) + 'branchia' (gill), descriptively naming these mollusks for the distinctive arrangement of their respiratory organs.
These ancient mollusks haven't changed much in 500 million years—their simple shield-shaped gills are so efficient that they've needed no improvement despite all of evolution's innovations!
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