Pennella balaenopterae is a large ectoparasitic copepod specialising in parasitising marine mammals.

The mandibles form a sucking tube for the mouth through which the species feed and adults also have a pair of segmented sensory antennae.

There have been recent records of this species parasitising pinnipeds, namely a northern elephant seal (Mirounga angustirostris) in the north Pacific[5] and from fin whale, (Balaenoptera physalus)[4] Cuvier's beaked whale (Ziphius cavirostris), Risso's dolphin (Grampus griseus), the bottlenose dolphin (Tursiops truncatus) in the Adriatic Sea[6] and harbour porpoise Phocoena phocoena relicta in the Aegean Sea.

[7] The early development of the larvae takes place in the egg sac while it is still attached to the female until it is released into the water column possessing a full set of cephalic appendages and three pairs of thoracic legs.

Males remain as free swimming copepodids but the females have a distinctive anchoring processes that extend from its anterior end.