plural noun
Ac·an·tho·dii | \ˌaˌkanˈthōdēˌī, ˌakən-\

Definition of Acanthodii 

: a subclass of Placodermi comprising primitive Paleozoic fishes having the anterior margin of each fin supported by a stout spine and often having one or more pairs of spines similar to the fin spines along the lower lateral part of the body between the paired fins of each side

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First Known Use of Acanthodii

1851, in the meaning defined above

History and Etymology for Acanthodii

New Latin, from Acanthodes

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The first known use of Acanthodii was in 1851

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a state of commotion or excitement

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