| Thetys vagina | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Tunicata |
| Class: | Thaliacea |
| Order: | Salpida |
| Family: | Salpidae |
| Subfamily: | Salpinae |
| Genus: | Thetys Tilesius, 1802 |
| Species: | T. vagina |
| Binomial name | |
| Thetys vagina Tilesius, 1802 | |
| Synonyms | |
Thetys costata(Quoy & Gaimard, 1825) | |
Thetys vagina, or thetwin-sailed salp, is the largest known solitary species ofsalp and the only valid species of thegenusThetys. First described byWilhelm G. Tilesius in 1802, the species is transparent and gelatinous, making it difficult to be seen in water, which is helpful in avoiding predators.[1][2][3] The fossil range is very recent.[4] Other animals often mistaken forT. vagina areSalpa fusiformis,Aurelia aurita, andPegea confoederata. There is no known status of conservation in this species.T. vagina DNA was sequenced as part of a larger project in 2014 wherespiny lobster larvae were found attached toT. vagina and consuming it.[5]
T. vagina can reach up to 333 mm (13 in) long.[6] They develop into two distinct forms; the aggregate generation and the solitary generation. The aggregated sexual blastozooids (aggregate form) can get to the size of 250 mm and have five muscle bands. The solitary asexual oozooids (solitary form) can get to size of 300 mm[7] and have around 20 muscle bands, which are characterized as “striped” with two short dark-colored tentacles at their ends, attached at the upper and lower halves of the body.[8] Both the aggregate and the solitary forms havetests covered in ridges and grooves. They have a colored digestive system seen as a dark or colorful lump.[8] The embryos have been found to be between 10-15 mm.[9]
Thetys vagina is found inpelagic marine environments.[10] It occurs intropical andtemperate waters of thePacific,Atlantic andIndian Ocean and is occasionally found in colder waters in the northern Atlantic, likely following warm water currents.[9][6][7] The species is widespread but at low density (although they may occasionally be found at very high density), resulting in only rare accounts of it being caught.[7]
Thetys vagina has been found off the central coast ofBritish Columbia, marking its north-most occurrence to date.[3] It has been found by cataloging volunteers along theWest Coast of the U.S. and reportedly congests nets of fisherman off the coast of northernHonshu and southernHokkaido, Japan.[7] In January 2009, the largest measured biomass ofT. vagina was recorded at 852 g WW m−3 in theTasman sea.[11]
Thetys vagina stays in thephotic zone and is often found in places of highchlorophyll concentration, likely due to itsphytoplankton rich diet.[7] A large increase ofT. vagina is associated with an increase inphytoplankton.[7] The ecology of this species is not fully understood.[7]
Like othersalps,T. vagina feeds by consumingplankton nutrient water on one end of its body, filtering it via an internal net made of mucus, and spewing the water out the other end.[3] Their internal net is very effective, catching particles spanning four magnitudes in size.[8] This action also allows them to move through thewater column, classifying them asnektonic.T. vagina feeds on marineplankton, including single-celled organisms such asdinoflagellates,silicoflagellates,diatoms, andtintinnids, as well ascopepods and other small particles.[7] Continuing up the food chain,T. vagina is preyed upon bymedusae,siphonophores,ctenophores,heteropods,sea turtles, late stage larvae of thespiny lobster, marine birds, along with various species of fish.[7] They have a high energy content at (11.00 kJ g−1 DW).[11]
In a study done in the Japan Sea in 2006, the gut contents of T.vagina were evaluated.[7] The diatomCoscinodiscus spp. (13–55 μm in diameter) was found to be the major makeup of the guts, with the diatomCoscinodiscus wailesii (219–313 μm) being the second most prevalent.[7] Another study off the coast of Maine found T. vagina gut content to be mainly made up of twodinoflagellates;Prorocentrummicans andDinophysis norvegica. The study also foundT. vagina to be an indiscriminate feeder over a broad size spectrum.[9]
Waste fromT. vagina is densely packed, sinks quickly, and is full of carbon. Their carcasses also sink quickly and are carbon rich (31% dry weight, DW).[11] This makes them efficient carbon sinks, but also harder to study. This carbon exchange could be responsible for up to 67% of the mean organic dailycarbon flux in the area.[11] In 2007 and 2009, theTasman sea floor was analyzed from 200m to 2500m in depth and large quantities ofT. vagina were found. The quantities found were some of the largestgelatinous zooplankton depositions ever recorded.[11] Further,benthic communities were found consumingT. vagina carcasses.[11] This sink provides nutrients to thesebenthic communities and are likely a large source ofcarbon input.[11]
The generic name ofThetys derives fromTethys orThetis, Greek mythological figures.[12][13] Tethys was the mother of river gods and the Oceanids, while Thetis was the goddess of water, a nereid, or a sea nymph. The species epithet isLatinvagina meaning "sheath" or "scabbard."[13][12] At the time of Tilesius' naming, the term had not acquired the modern-day anatomical meaning and simply meant a sheath, likely referring to the salp's appearance.[12]
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