What on earth is this? (two ID's and one question)

[Greyhaven7]

This wasn't in my tank earlier today (around 3pm) when I went to feed my lil guys, but at around 9pm I spotted this weird bubble coming out of my substrate (bubble is about 1.5 inches in diameter). It looks like some kind of egg sac, but I don't have a clue. The "stalk" it's attatched to wasn't there either, but hasn't moved, despite the fact that the "bubble" is gone now. I didn't notice any obvious motion other than the bubble "blowing" in the current. Any ideas?

image from about an hour later when the "bubble" had deflated.

I'm assuming these lil' bastages are aiptasia?

Is it ok that my tank is home to what appers to be thousands upon thousands of these little guys (copeopods I think they are) and a hundred or so flatworms (as seen on the upper left of the rock). I know they're harmless/beneficial, but in the numbers that I have them in, I don't know... (55gal).

 

[DragonForce]

It looks like it could be an egg sac of some sort.

Those could very well be aptasia but it's hard to tell in the pic.

The things on the class are pods.

As for the flat worms, you can try taking them out when you see them. They can be little "bastages" if their numbers get out of control. I also think there are a few critters that eat them but you might have to look into that or maybe someone else can comment.

Also, peppermint shrimp should take care of the aptasia for you(mine little guy did) if you dont want to deal with removing them yourself.

 

[Greyhaven7]

I had a pepermint, but he disappeared months ago. =(
Perhaps victim of the 2.5 inch pink bristle worm I discovered the other day. The worm was in a small (3 inch diameter) piece of live rock I got for free with my Emerald crab. I took the whole rock out (checked for other critters) and boiled it in fresh water. >=) I think he's dead now.

I really want to know what the bubble thing is. I'm usually pretty good at this stuff, but if that thing isn't an egg sack, I don't know WHAT it is.

 

[DragonForce]

I think I remember reading something about nassarius snails reproducting with a mucus like sac or something along those lines.

Do you have any corals or anything? It could just be a big ball of slime.

 

[Greyhaven7]

I never actually saw the Nassarius snail "come up" near the bubble, but I will look into that. I did, however, see him leave. I couldn't watch the whole time, so it's entirely possible it was something he made.

No corals (that i'm aware of yet). The ball seemed hollow. It's hard to tell from the pic, but the "dots" or "eggs" or whatever they are are in a shape resembeling a bubble within a bubble. There are two layers of eggs, but nothing in between or in the middle. It also moved as if it were hollow, when the current would bend it down to the substrate, it would lightly bounce back as though there were nothing in it.

 

[Stuart]

Might be worth looking up chordates like salps - they have a similar configuration - just never seen them in aquaria - just under a microscope

 

[Fluff]

Well, I could be totally off but the first pic to me looks like a spaghetti worm and the sac could maybe bit it's way of spawning? Just a guess. The second pic looks like hydroids to me but it could be very tiny aptasia. Are they the only ones you have?
Third pic looks like amphipods. The flatworm on your glass is a copepod eating species and is totally harmless so don't go nuking your tank. Their numbers will fluxuate depending on the food source. I used to see them off and on but haven't seen any in a long time.