Elysia coodgeensis

[aukerda]

Found a new hitchhiker the other day that I believe I've ID'd as Elysia coodgeensis (http://www.nudipixel.net/species/elysia_coodgeensis/) although I haven't been able to get a good picture to get second opinions on this. It appears that this is probably harmless, I haven't added any rock or anything to the tank for a few months, and nothing has come up missing or died unexpectedly. When I first noticed him though, he was sticking out of a rock a bit and emitting puffs of a white fluid. It wasn't think and milky and seemed to dissolve in the water column quickly. Not knowing what it was doing, I tried to capture the critter, but was unable to. I saw him again this morning on the rockwork but he moved pretty quickly once the lights came on. Should I be concerned?

[jefathome]

Hmm... How well have you seen him?
Sounds like breeding behavior and one of the few "hitch-hikers" I know of that would do that are Stomapods.

[aukerda]

I'm seen him really well. Has no shell and moves with what looks to be a foot as he glides over the rock work. He's about an inch or so in length and can stretch from rock to rock. This morning I noticed what appeared to be a flat shell on his back, but his "skin" wraps over it. I think shell may be pliable judging by the size of the holes he's gone into.

[VacavilleFC3S]

i think it's a stomatella snail..

[aukerda]

Maybe a stomatella snail.... I found this video http://www.youtube.com/watch?v=-n7pG9ZKOcs which looks very close, although mine doesn't appear to be that "spikey". But that shooting of goo is exactly what I saw.

[Elysia]

It seems unlikely that you would get a hitchhiker from New South Wales, unless you are importing some cherry Australian corals. And Elysia spp. do not have shells. Nor would they be fleeing the light, as most (all?) retain plastids from their alga food that allow them to essentially photosynthesize. Further, the species that I am familiar with do not engage in broadcast fertilization.
There is a lot of variety in how the stomatellas look, but they do have small, delicate shells (often described as looking like fingernails), move realitively quickly, often hide from direct light.