plural noun
Eph·e·mer·i·dae | \-əˌdē\

Definition of Ephemeridae 

: a family of large mayflies that include forms having shining transparent wings as adults and as nymphs very large mandibles curved out at the tips, feathered gills extending over the body, and enlarged front legs adapted for digging in stream and lake bottoms

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History and Etymology for Ephemeridae

New Latin, from Ephemera, type genus + -idae

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