Sandy silk cacoon

Trixter227 · Feb 1, 2023

Hey just looking for some help, ive noticed a small "caccoon" seen like its made of a silk or soft substance. This was one of the first frags placed in tank. Its been about 6 months since and now i see a new one.
But its built on the glass this time so we can creep on it.

First picture is original, 2ed is new within a day or 2. You can see the "shrimp" like creature with alot of leggs.

ISpeakForTheSeas · Feb 1, 2023

Based on the general shape and the two openings in them, the “cocoons” appear to be solitary tunicates (harmless filter feeders), so the crustacean being there is just coincidence.

Trixter227 · Feb 1, 2023

Thank you for the reply, im not sure its just coincidence as its been there for 2-3 days and opens and closes the ends with sand bits. It appears to have "tentacles' it sticks out and pulls bits in.

Trixter227 · Feb 4, 2023

Bump, it moved further down the glass. Definitely makeing the cacoon. Durring feeding it stick 2 antenna out one side and pulls food in.

ISpeakForTheSeas · Feb 4, 2023

trixter227 said:
Bump, it moved further down the glass. Definitely makeing the cacoon. Durring feeding it stick 2 antenna out one side and pulls food in.

There are some shrimp-like crustaceans that make tubes (such as tube-building amphipods), but none that I'm aware of make cocoons/structures that look like this. There are also some shrimp-like crustaceans that are commensal organisms with tunicates (typically living inside the tunicates).

Do you have any videos of the crustacean interacting with the cocoon or of the two antennae coming out to feed? Pics could work for the antennae coming out too, but video would be best for any interactions.

Trixter227 · Feb 4, 2023

1st vid shows it eating? And just moveing about

2ed vid he flips over and even picks up a chunk of sand, watchin it seems its building the tube. Spins around while moveing sand bits?

3rd shows the antenna out of the tube.
I love finding new life in our tanks.

ISpeakForTheSeas · Feb 4, 2023

trixter227 said:
1st vid shows it eating? And just moveing about

2ed vid he flips over and even picks up a chunk of sand, watchin it seems its building the tube. Spins around while moveing sand bits?

3rd shows the antenna out of the tube.
I love finding new life in our tanks.

Ah, okay, yeah that's not what I though you were asking about here (I thought you were asking about the thing behind the snail in the first pic, and the translucent thing under the crustacean in the second and third pics). Yeah, yours is definitely building a tube. I'm not very good with ID'ing tiny crustaceans like this, but I know there are tube-building amphipods and tanaids, both of which occasionally find their ways into our tanks.

Either way, these guys should - to my knowledge - be harmless (and if they get out of hand, I'd imagine a wrasse or similar would be able to control their population pretty effectively). Neat find (IMO) and good videos of it.