Underwater Antarctic biodiversity (French scientific base in Antarctica). Identified as <i><a href="https://en.wikipedia.org/wiki/Diplulmaris_antarctica" class="extiw" title="w:Diplulmaris antarctica">Diplulmaris antarctica</a></i> by Prof. <a rel="nofollow" class="external text" href="http://www.ib.usp.br/~acmorand/">Andre C. Morandini</a>:
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<td valign="top" style="border: none; padding: 4px 10px;">Sometimes it is not so easy to identify animals by photographs, but in this case we can see some important features.<br><br><p>It is a scyphozoan jellyfish of the order Semaeostomeae, due to the general body shape but mostly because of the marginal tentacles and elongated oral arms.<br>
It is a member of the family Ulmaridae because the gastric cavity is divided in canals, as can be seen by transparency.<br>
Subfamily Ulmarinae because tentacles arise from the margin and gonads are protrusive (the orange pleated tissue in the center).<br>
The difference between the genera of this subfamily (<i>Diplulmaris</i>, <i>Discomedusa</i>, <i>Floresca</i>, <i>Parumbrosa</i>, <i>Ulmaris</i>, <i>Undosa</i>) are the number of sense organs (rhopalia) and the number of tentacles, besides some canal system organization.<br>
As far as I can see the animal in the photo has 21 tentacles and 10 rhopalia (probably more of both). But the angle of the image does not allow me to see more.<br><br>
I think it is a <i>Diplulmaris antarctica</i>, by the way from all valid species of the subfamily, this is the only one known from Antarctic waters. The species has 16 sense organs and 16-48 tentacles.<br>
If you Google it, at least the first images are OK.
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<a href="//commons.wikimedia.org/wiki/User:AMICE" title="User:AMICE">Erwan AMICE</a>
CC BY 4.0
<a href="//commons.wikimedia.org/wiki/File:Ice_planet_and_antarctic_jellyfish.jpg" title="File:Ice planet and antarctic jellyfish.jpg">File:Ice_planet_and_antarctic_jellyfish.jpg</a>