First described by W.G Tilesius in 1802, the species is transparent and gelatinous, making it difficult to be seen in water, which is helpful in avoiding predators.

[4] Other animals often mistaken for T. vagina are Salpa fusiformis, Aurelia aurita, and Pegea confoederata.

[7] Thetys vagina has been found off the central coast of British Columbia, marking its north-most occurrence to date.

[7]  In January 2009, the largest measured biomass of T. vagina was recorded at 852 g WW m−3 in the Tasman sea.

[11] Thetys vagina stays in the photic zone and is often found in places of high chlorophyll concentration, likely due to its phytoplankton rich diet.

T. vagina  feeds on marine plankton, including single-celled organisms such as dinoflagellates, silicoflagellates, diatoms, and tintinnids, as well as copepods and other small particles.

[7] Continuing up the food chain, T. vagina is preyed upon by medusae, siphonophores, ctenophores, heteropods, sea turtles, late stage larvae of the spiny lobster, marine birds, along with various species of fish.

[11] In 2007 and 2009, the Tasman sea floor was analyzed from 200m to 2500m in depth and large quantities of T. vagina were found.

[12][13] The former being the mother of river gods and the Oceanids, and the latter being the goddess of water, a nereid, or a sea nymph.