Very often the basal segment of the protopodite bears, on the outer side, a lamellar appendage (more rarely, two), the epipodite, which may function as a gill.
Protopodite, endopodite, exopodite, and epipodite were considered to be the morphological units of the crustacean limb.
It is by the specialization of two " endites " that the endopodite and exopodite of higher Crustacea are formed, whilst a flabelliform exite is the homogen or genetic equivalent of the epipodite (see Lankester, " Observations and Reflections on Apus Cancriformis," Q.
(4) Three of the rami of the primitive limb (endites 5 and 6, and exite I) specially developed as endopodite, exopodite, and epipodite - the first two often as firm and strongly chitinized, segmented, leg-like structures; the original axis or corm reduced to a basal piece, with or without a distinct gnathobase (endite i)- typical tri-ramose limb of higher Crustacea.
Fl, The flabellum which becomes the epipodite of higher forms.