''Kowalevskia'' is a genus of

larvacean Larvaceans, copelates or appendicularians, class Appendicularia, are solitary, free-swimming tunicates found throughout the world's oceans. While larvaceans are filter feeders like most other tunicates, they keep their tadpole-like shape as adu ...

tunicate Tunicates are marine invertebrates belonging to the subphylum Tunicata ( ). This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...

s, the only one in the family Kowalevskiidae.

Species

* '' Kowalevskia oceanica'' Lohmann, 1899 * '' Kowalevskia tenuis'' Fol, 1872

Description

''Kowalevskia'' is a small larvacean. In the adult, the body measures around 1 mm long, while the tail is 8 mm long, appearing stretched and tapered at its ends. Unlike other

Appendicularia Appendicularia may refer to: * ''Appendicularia'' (plant), a genus in the plant family Melastomataceae * Larvacean, an animal of the class Appendicularia in the subphylum Tunicata ** ''Appendicularia'' (animal genus), a genus in the larvacea ...

species, ''Kowalevskia'' doesn't have a heart. Instead, the circulatory system is powered by the beating tail. ''Kowalevskia'' also lacks an endostyle, being replaced by a ciliated groove without glandular cells. The spiracles also differ from other families, being shaped as long, narrow slits.

House

Uniquely among larvaceans, ''Kowalevskias house is ellipsoidal or toroidal in shape, 1 to 2 cm in diameter. It has a single opening, acting both as inlet and outlet.

Distribution

Both species of ''Kowalevskia'' have a wide distribution. ''K. tenuis'' can be found in the East Atlantic and West Pacific, as well as in the Mediterranean and Black Seas. Meanwhile, ''K. oceanica'' is found in the Mediterranean and North-East Atlantic, as well as in the Red Sea and West Indian Ocean.

Phylogeny

The monotypic Kowalevskiidae is believed to be the sister taxon to

Fritillariidae Fritillariidae is a family of tunicates belonging to the order Copelata. Genera Fritillariidae comprises three genera, divided into two subfamilies. While the trunk anatomy differs between the genera, they share a similar arrangement of house ...

, with both sharing specialized characteristics and forming a clade to the exclusion of

Oikopleuridae Oikopleuridae is a family of larvacean tunicates. A comparatively species-rich family, it has been especially well-researched thanks to the ubiquity of ''Oikopleura dioica'' as a model species. It comprises two subfamilies, Bathochordaeinae and O ...

References

Appendicularia Tunicate genera {{tunicata-stub