Hrabea ogumai is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of oligochaete worm

Worm

The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...

 originally described by Yamaguchi in 1936 from specimens collected from subterranean waters in Sapporo. The genus is named after the great oligochaete specialist Dr. Sergej Hrabe, and the species after Prof. K. Oguma.

The body of Hrabea is 7–8 cm (2.8–3.1 ) long, and consists of 146–183 segments. The body wall is thin and transparent, but when illuminated, shows a light green tint. It swims actively by lateral undulating

Undulatory locomotion

Undulatory locomotion is the type of motion characterized by wave-like movement patterns that act to propel an animal forward. Examples of this type of gait include crawling in snakes, or swimming in the lamprey...

 movements. The setae are one-pointed.

Hrabea ogumai is similar to Stylodrilus subgenus Bythonomus, but lacks the transversal vessels of the middle and posterior parts of the body, has one testis and male funnel (in segment X) instead of two (in segments IX and X), and has a pear-shaped atrium, to which the vas deferens

Vas deferens

The vas deferens , also called ductus deferens, , is part of the male anatomy of many vertebrates; they transport sperm from the epididymis in anticipation of ejaculation....

is connected at the apical end, rather than at the lower half.