[Jennifer]

I have new little sessile bulbs in the aquarium, translucent, and barely larger than 1/4 inch diameter. They don't appear (yet?) to have any tentacles, and most of them have a shape similar to an Indian Wedding Vase, with two small opennings opposite one another at the top of the bulb. There are 4 that I can find, all on the same piece of live rock. Anyone with any ideas? I'm snowed in today and can't find any pictures that suit it online, though I might not be trying to right search criteria.

[leebca]

This was originally posted in the Saltwater (Fish-Only) Forum where I don’t think it will get as much attention as it should. I moved your post to the Reef Aquariums Forum where those with more experience and knowledge of invertebrates and live rock hitchhikers may be better able to help you.

Good luck!

[Ninong]

Tunicates?

[Ninong]

Detail of young tunicate:

CLICK HERE TO SEE A YOUNG TUNICATE

[zhenya]

Here's another link to the article about tunicates
Tunicates or Sea Squirts: A Wet Link by Ronald L. Shimek, Ph.D. - Reefkeeping.com

[Jennifer]

That is EXACTLY what they are

My first question was going to be: does their existance in my tank mean something is out of balance? Though reading the Spineless Column article, it sounds like they are fussy about their water, and probably wouldn't be there if the water were unhealthy for the fish.

My other question, rising from that same article, it sounds like they might start to take over the tank. Is there anything I should worry about? I don't have any corals in the tank (I haven't wanted to buy any until I am absolutely positive I have the water quality set, they are expensive, and I don't want to waste that much money on my own inexperience). The slowest creatures I have are my snails, and I would hope these things won't grow fast enough to envelope one of them over night, so I should (?) see it in the process and be able to move the snail. Anything else I should be watching for or being careful of?

Thank you so much for identifying these things for me, I love to have as much information as possible on the things that grow and live in my tank so I can plan the best ways to take care of them. You guys are awesome!

[Ninong]

Originally Posted by Jennifer

That is EXACTLY what they are

Your description left little doubt as to what they probably were. The opening at the top of the animal is the inhalent siphon and the one on the side is the exhalent siphon. Tunicate larvae are called tadpoles because they look a lot like frog tadpoles. When they settle, the head attaches to the substrate and they discard the post-anal tail. They extrude a celluose casing (tunic) to shield the body. After settlement and attachment to the substrate, the internals of the animal rotate around to face upwards. Remember that what used to be its head is now attached to the substrate. Believe it or not, these extremely primitive animals are very primitive chordates. In the larval stage, they actually have a notochord (rudimentary spine) and a tail. They might be a very early link between invertebrates and vertebrates.

My first question was going to be: does their existance in my tank mean something is out of balance?

No, not at all.

Though reading the Spineless Column article, it sounds like they are fussy about their water, and probably wouldn't be there if the water were unhealthy for the fish.

There are many different species in all sizes and colors. Some are translucent. Yours are apparently very young. I don't believe any of them have very long lifespans. We're probably talking about a year or so max. Another common name for them is sea squirt. That's because some of them (the larger ones) will be torn up in storms and tossed on the beach and then when you step on one, water squirts out. They look kinda slimey and they feel weird if you step on one. I have seen them on beaches in Big Sur following storms when I lived in California.

My other question, rising from that same article, it sounds like they might start to take over the tank.

I doubt it. I would be surprised if you still have any at all three or four months from now.