Flat shrimp like creature + soft transparent coral-like creature?

[Kokofish_2022]

First pic
This creature is about the size of a large, adult Gammarus amphipod but very flat and longer. The "scissors" that it has on its head was pretty flat and I remember there were tiny hairs moving back and forth within the inner lining. It has lots of feet underneath and I saw it swimming around like how an amphipod or a tiny shrimp would, but it prefers to sit on the rock. I believe that long dark line running in the middle throughout its body are the contents of what it ate. I only ever saw it once. It retreated to one of the tiny caves in the rock, struggling to get inside.

Second pic
It contracts its "mouths" if I touch it. It has been sitting in the "corner" of my low flow area. Last I remembered, it had 2 mouths and more compact and now it has 3 mouths and starting to spread out. It has neither the stalk nor the long tentacles of an aiptasia. It's tentacles are super short and very close to its mouths if it even has any tentacles. Also notice the ring of white dots around each of its mouths.

Additional background
Tank is about 3 weeks old and the live rock is purchased from KP Aquatics that has an aquaculture farm off the coast somewhere in southern Florida. After removing the heater (it gets pretty warm at my place), tank temp has decreased to around 77F from around 83F and has been stable around 77F +/- 2F ever since last week. It is when the temp has decreased slightly that more life started to pop out.

 

[EeyoreIsMySpiritAnimal]

First pic
This creature is about the size of a large, adult Gammarus amphipod but very flat and longer. The "scissors" that it has on its head was pretty flat and I remember there were tiny hairs moving back and forth within the inner lining. It has lots of feet underneath and I saw it swimming around like how an amphipod or a tiny shrimp would, but it prefers to sit on the rock. I believe that long dark line running in the middle throughout its body are the contents of what it ate. I only ever saw it once. It retreated to one of the tiny caves in the rock, struggling to get inside.

Second pic
It contracts its "mouths" if I touch it. It has been sitting in the "corner" of my low flow area. Last I remembered, it had 2 mouths and more compact and now it has 3 mouths and starting to spread out. It has neither the stalk nor the long tentacles of an aiptasia. It's tentacles are super short and very close to its mouths if it even has any tentacles. Also notice the ring of white dots around each of its mouths.

Additional background
Tank is about 3 weeks old and the live rock is purchased from KP Aquatics that has an aquaculture farm off the coast somewhere in southern Florida. After removing the heater (it gets pretty warm at my place), tank temp has decreased to around 77F from around 83F and has been stable around 77F +/- 2F ever since last week. It is when the temp has decreased slightly that more life started to pop out.

I don't know what either of them are but will be following for updates! Did you try reaching out to KPA for identification?

 

[Kokofish_2022]

I don't know what either of them are but will be following for updates! Did you try reaching out to KPA for identification?

Good idea. I'll see if I can reach out to them.

 

[MWFoster]

The first one you want out of your tank quick it looks like a young Mantis shrimp. It behaves like one also they usually come out at night so look for it then. Once it gets bigger it will kill and eat anything swimming in your tank.

The second one looks almost like a Flower anemone but they are usually a single head and the one shown is clearly 3 attached heads.

 

[BZOFIQ]

Hard to tell but I'd say first one is a pistol shrimp.

 

[homer1475]

I would say first pic is baby mantis(both claws are the same size so not a pistol). Also mantis shrimp are known to come in live rock from the gulf.

Second looks to me to be a sponge.

 

[Kokofish_2022]

The first one you want out of your tank quick it looks like a young Mantis shrimp. It behaves like one also they usually come out at night so look for it then. Once it gets bigger it will kill and eat anything swimming in your tank.

The second one looks almost like a Flower anemone but they are usually a single head and the one shown is clearly 3 attached heads.

It will be very hard to capture the first one when it is small like that. It moves kinda fast and can squeeze through the small cracks in the rocks. I don't even know what it likes to eat and I don't want to take out my whole rocks just for a single unknown shrimp-like critter. I have not seen it out since, day or night. I'll keep an eye on it and hopefully I can capture it and put it in my smaller second tank for observation as it grows.

 

[Argentum]

I agree the second picture looks like a sponge to me, but the first reminds me of a very, very small slipper lobster. No clue what their life cycle is, but that's just the first thing that popped into my mind when I saw the pic.

 

[OldRed1]

Second photo possibly a tunicate?

 

[sculpin01]

Not a young mantis shrimp. It's a Tanaid, a harmless burrowing detrivore.

Tanaidacea - Wikipedia

en.wikipedia.org

 

[sculpin01]

Second could be a sponge-associated zoanthid, but not certain.

 

[Kokofish_2022]

Not a young mantis shrimp. It's a Tanaid, a harmless burrowing detrivore.

Tanaidacea - Wikipedia

en.wikipedia.org

The body structure is very very similar to the Tanaid you mentioned! Except this one has those flat scissor like things at its head. Also it is very similar to some of the google images I found.

 

[vetteguy53081]

First one is pistol baby and other may be a nudibranch in which FEW are beneficial and should be removed before it lays eggs if fertile

 

[sculpin01]

Tanaids are actually quite common in reef tanks but since they tend to live in the substrate are rarely seen.

 

[sculpin01]

Apparently there are multiple Parazoanthus and Epizoanthus zoanthids associated with Caribbean sponges. See for instance:

https://www.bio.fsu.edu/wulff/Swain%20&%20Wulff%202007.pdf