The range of modification of which the rami or limb-branches of the limbs of Arthropoda are capable is very large, and in allied orders or even families or genera we often find d z what is certainly the palp of the same appendage (as determined by numerical position of the segments) - in one case antenniform, in another chelate, in another pediform, and in another reduced to a mere stump or absent altogether.
They are frequently organs of attachment in parasitic Copepoda, and they may be completely pediform in the Ostracoda.
In a few Ostracoda, by a rare exception, the masticatory process is reduced or suppressed, and the palp alone remains, forming a pediform appendage used in locomotion as well as in the prehension of food.
These, with the main stem more or less pediform, have the epipod and exopod modified for respiratory purposes.
The variable first maxillae are seldom pediform, their function being concerned chiefly with nutrition, sensation and respiration.