Could it be an ephyra?

I'm not an expert but it doesn't look like the ephyras that I've seen in the books. However I'll look into the scyphozoans group. Thanks Ana!

I suggest you to contact Gill Mapstone (NHM in London), at [email protected], as your animal resembles an early stage or a part of of a physonect siphonophore (Hydrozoa). I attach herein her last review on the global diversity of this group. In your pic I see six tentacles in two orders, and the rounded structures below them may look like small nectophores. 

Thank you Stefano. I was just looking into siphonophores after seeing some pictures in Trégouboff's book.

Thank you two for your help.

Hi, for me is a protista, radiolaria, Acantharea. Best regards

Hi, I have problema with the size.. But if you see the Acanthometra in the internet is very similar. Best regards

Guessing..... a foraminifer imposed on a pennate diatom!

Thanks Ana and Dola for your ideas. The scale bar in my picture represents 1mm so I think that it's too big for an Acantharia. After consulting some sources I agree with Stefano that seems an early stage of siphonophore.

Thanks again for your help.

thank you for adding this question and for solving the puzzle. Can you please add the sources that you used or the identification plate? Thank you in advance 

Acantharia are planktonic, free living, exclusively marine protozoa, ranging in size from 0.05-5 mm in diameter. Not problem with the size..Plate from Ernst Haeckel's Kunstformen der Natur (Artforms of nature) (1904). I sow this plate in internet.

Best regards

These are the sources I used. I got the first clue looking at the Siphonophores Physonectes plate in:

Tregouboff, G., & Rose, M. (1957). Manual de Planctologie Mediterranee. CNR S., Paris.

After that I checked:

Kirkpatrick, P. A., & Pugh, P. R. (Eds.). (1984). Siphonophores and velellids: keys and notes for the identification of the species (Vol. 29). Brill Archive.

Of course I searched on internet  about physonectes and with the naked eye I think it is alike a  Physophora gender:

http://www.marinespecies.org/aphia.php?p=image&pic=73949

Even I found a picture of a Physophora hydrostatica early stage and it looks very similar (attached).

I also contacted with the expert that Stefano told me, but I havn't had any answer yet.

It's been a pleasure to discuss with all you the identity of this "stranger". Thanks again!

Wow, from the first picture I was thinking that it was a stage of brittle star; however, after seeing the 2nd picture, it definitely looks more jelly-like...very interesting!