''Placentonema gigantissima'' is a giant

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

that parasitizes the

placenta The placenta (: placentas or placentae) is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas, and waste exchange between ...

and other tissues of the

sperm whale The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the Genus (biology), genus ''Physeter'' and one of three extant species in the s ...

. With a length of and a diameter of , it is potentially the largest nematode worm ever described, inhabiting one of the largest mammals in the world. It was discovered in the 1950s around the

Kuril Islands The Kuril Islands or Kurile Islands are a volcanic archipelago administered as part of Sakhalin Oblast in the Russian Far East. The islands stretch approximately northeast from Hokkaido in Japan to Kamchatka Peninsula in Russia, separating the ...

Taxonomy

''Placentonema gigantissima'' was described in 1951 by Russian

parasitologist Parasitology is the study of parasites, their hosts, and the relationship between them. As a biological discipline, the scope of parasitology is not determined by the organism or environment in question but by their way of life. This means it f ...

and

helminthologist Helminthology is the study of parasitic worms (helminths). The field studies the taxonomy of helminths and their effects on their hosts. The origin of the first compound of the word is the Greek '' ἕλμινς'' - helmins, meaning "worm". In ...

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 In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

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

The body is very long, cylindrical, tapering at the ends, with a transparent cuticle. The oral orifice is oval shaped with two simple lateral lips, while the esophagus is divided into two parts, one muscular and glandular. Males are 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 are oval, 0.05 mm long by 0.03 mm wide, and the young inside the eggs are completely formed.

Life cycle

''Placentonema gigantissima'' utilizes nutrients found in the endometrium of female sperm whales. It forms spiriud (small, embroyonated) eggs. It can parasitize not only the placenta, but also the

uterus The uterus (from Latin ''uterus'', : uteri or uteruses) or womb () is the hollow organ, organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic development, embryonic and prenatal development, f ...

, reproductive tract,

mammary glands A mammary gland is an exocrine gland that produces milk in humans and other mammals. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in primates (for example, human ...

, and subdermis of the sperm whale. It is commonly found in pregnant sperm whales. Much of the life cycle of ''P. gigantissima'' is unknown.

Distribution

This species is found inside female sperm whales that inhabit lower latitudes of the southern hemisphere.

External links

''Placentonema gigantissima'' was discussed on

RNZ Radio New Zealand (), commonly known as RNZ or Radio NZ, is a New Zealand public service broadcaster and Crown entity. Established under the Radio New Zealand Act 1995, it operates news and current affairs station, RNZ National, and a classica ...

Critter of the Week ''Critter of the Week'' is a weekly RNZ National programme about endangered and neglected native plants and animals of New Zealand. Beginning in 2015, ''Critter of the Week'' is an approximately 15-minute discussion between Nicola Toki (origi ...

''
24 November 2023

References

Nematodes described in 1951 Spirurida Parasitic nematodes of mammals Whales {{Secernentea-stub