''Yamaguchia toyensis'' is one of many aquatic oligochaetes belonging to the family

Lumbriculidae The Lumbriculidae are a family of microdrile oligochaetes common in freshwater environments, including streams, lakes, marshes, wells and groundwater. They should not be confused with the earthworm family Lumbricidae. Many species and genera are ...

discovered on the island of

Hokkaidō is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The la ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

, which seems to be one of three "hotspots" of lumbriculid diversity (the others being the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...

and

Lake Baikal Lake Baikal (, russian: Oзеро Байкал, Ozero Baykal ); mn, Байгал нуур, Baigal nuur) is a rift lake in Russia. It is situated in southern Siberia, between the federal subjects of Irkutsk Oblast to the northwest and the Repu ...

). The genus named after the great oligochaete taxonomist Professor Hideji Yamaguchi. ''Y. toyensis'' was originally collected from profundal parts of Lake Tōya, Hokkaido (after which it is named), and is among the shortest of the lumbriculids (7–11 mm). It is uncertain where in the

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

of the lumbriculids ''Y. toyensis'' belongs. It seems to lack novel characters with which to place it unambiguously, but has a combination of features not found in other genera of the family: testes and atria in segment X, a single, prosoporous male funnel per atrium, and spermathecae in segment XI.

References

* Lumbriculidae Fauna of Japan Hokkaido region Animals described in 2004 {{annelid-stub