Placentonema gigantissima

Placentonema gigantissima is a giant nematode that parasitizes the placenta of the sperm whale. With a length of 8.4 m and a diameter of 2.5 cm, it is potentially the largest nematode worm ever described, inhabiting the largest mammals of the world. It was discovered in the 1950s around the Kuril Islands.

Taxonomy
Placentonema gigantissima was described in 1951 by Russian parasitologist and helminthologist Nikolai Mikhailovich Gubanov.

Originally described from the family Crassicaudidae, it is now classified in the subfamily Crassicaudinae of the roundworm family, Tetrameridae.

It is a monotypic genus that differs from the only other genus in the subfamily, Crassicauda, by its "caudal alae, stub-like papillae and multiple uterus branching into 32 uteri".

Description
Body very long, cylindrical, tapering at the ends, with a transparent cuticle. Oral orifice oval shaped with two simple lateral lips, esophagus with two parts, one muscular and glandular.

Males up to 3.75 m long and 9 mm wide; females up to 8.4 m long and 2.5 cm wide, with up to 32 ovaries. Mature eggs oval, 0.05 mm long by 0.03 mm wide, and the young inside the eggs are completely formed.

Life cycle
Placentonema gigantissima develops its parasitic nature by utilizing nutrients found in the endometrium of female sperm whales and forming as spiriud (small, embroyonated) eggs.

It can parasitize not only the placenta, but also the uterus, reproductive tract, mammary glands, or subdermis of the sperm whale. It is commonly found in pregnant sperm whales.

Much of the life cycle of P. gigantissima is unknown.

Distribution
P. gigantissima is found inside female sperm whales that inhabit lower latitudes of the southern hemisphere.