In zoology, a gill or respiratory system without distinct pores; gills that lack specific openings for water flow.
From apo- (away from) + poro (pore) + branchia (gill), from Greek branchion. The term describes gills that lack the characteristic pore structures found in other gill types.
Some mollusks and ancient marine creatures had aporobranchiate gill systems that allowed them to filter water in a completely different way than modern fish—it's like comparing two totally different water-filtering vacuum designs.
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