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(phylum Mollusca, class Cephalopoda)

A subclass of cephalopods which have one pair of gills. The true shell, if it occurs at all, is internal. The head possesses eyes and a mouth that bears a pair of mandibles and a radula. Eight arms extend from the head. Some forms also have two additional, retractile tentacles. A hyponome is also present. There are four extant orders and one extinct order. The subclass first appeared in the lower Carboniferous.

Subjects: Zoology and Animal Sciences.

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