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Retracting thing + others unknowns ?

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After some fights with algae using peroxide for a week in an empty tank + water conditions stabilizing after 2 more weeks with an external filter running additional filtration media, I see new life appearing in my otherwise not populated aquarium.


I'm trying to get an ID on the followings:




Small thing (about 1cm in length) with a pointy tip on top. I've tried to touch it with some tweezers and it retracts and flattens. Then in few minutes it relaxes again. It is hard to spot, but is just in the middle of the photo - macro shot:






Some green round 'grass leaves' about 2-3 mm in diameter - I like the looks I have few here and there:






Some young worm ? I saw something like this but it was huge compared to the fellow below which doesn't have more than 4 mm in diameter when open. One white and spotted another one with yellow:






Snails - I have a few. Some white, some black, some yellow, and it is difficult to get a clear shot of them.




Thank you for your answers,

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1. Tunicate

2. +1 to cool looking algae, could be Acetabularia

3. +1 to feather duster

4. +1 to Stomatella

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Hmmm it can actually be a tunicate! But a very young one I guess ?


It doesn't move at all, although I noticed it is more open today and little feeding holes appeared all around it:





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It looks really fascinating.


The tunicates that I've seen in my rockwork have all been rather tiny, from centimeter to 2-3 centimeter wide colonies. I hope I'll get a large colony some day. They are interesting creatures.

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Thanks, you were right with Acetabularia - it is so ... although mine are really small and not tall at all. I read an article saying that the lifespan is short in the aquarium, and I have few here and there. They are very green and not as dense as they appear in the mature photos I see online. I hope I will have them longer than the 'short term' described :D


About the retracting thing, it's weird a bit. It also has a hole in the middle (it is visible better in the second photo above) where it looks like it splits. Then little other holes all around it - so I have no idea what it is - the sea squirts look much taller than this one and with different openings though. The only thing that matches the description - but not the looks - seems to be the colonial tunicate -> http://nathistoc.bio.uci.edu/Tunicates/Colonial2.htm . So each syphon eats but they share a common excurrent syphon.


I will monitor it :)

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Sea squirt is just the layman's term for tunicate. Tunicates vary drastically in shape, size and color between different genus and different species. You most definitely have a colonial tunicate, you will just never know what species it is. You may be able to find the genus if you looks really hard in the right places.

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