Rhynchelmis is the genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of 30 species of aquatic oligochaetes from the Northern Hemisphere, with 11 species from North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and 19 from Eurasia

Eurasia

Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

. They are part of the family Lumbriculidae

Lumbriculidae

The Lumbriculidae are a family of microdrile oligochaetes common in fresh-water environments, including streams, lakes, marshes, wells and ground-water. They should not be confused with the earthworm family Lumbricidae. Many species and even genera are highly endemic, mainly in Siberia and the...

, which are among the largest of the microdriles. They are generally defined as having atria in segment X and spermatheca

Spermatheca

The spermatheca , also called receptaculum seminis , is an organ of the female reproductive tract in insects, some molluscs, oligochaeta worms and certain other invertebrates and vertebrates...

e in segment VIII (Fend & Brinkhurst, 2000). The prostomium

Prostomium

Prostomium is the first body segment in annelid worms. It is in front of the mouth, being usually a small shelf- or lip-like extension over the dorsal side of the mouth. It sometimes bears antennae and eyes. It often functions like a kind of overlip when the animal is feeding...

 generally has a proboscis

Proboscis

A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...

, from which the genus has got its name.

Rhynchelmis contains several subgenera, all of which have previously held genus rank: Rhynchelmoides with four species, Sutroa with six species, and Pseudorhynchelmis with nine species. Further, four species - Rh. aleutensis, Rh. brooksi, Rh. malevici and Rh. orientalis

Rhynchelmis orientalis

Rhynchelmis orientalis is a freshwater worm.It was described by Yamaguchi in 1936 from specimens collected on Hokkaidō. It can be distinguished from other species in the genus by "the possession of very long spermathecae running in several posterior segments into spermsacs and having no...

- cannot positively be placed in any of the subgenera.