Hitchhikers

[rabidric]

Hi all, we've only been at this marine lark for a while and there are so many things to learn! Todays question is regarding hitchhikers on live rock and attitudes to them. We have quite a lot of live rock given the size of the tank, probably 15+kg's(I know it's cost over £200 at £12/kg but I don't keep a tally on what I spend so don't know exactly) in an Orca and it's amazing what appears after a month or so. We've seen crabs and worms and other scuttling things and generally leave them well alone, but last night we spotted something that looked like a garden slug but it had a very small irridescent shell. Difficult to give a size as like a slug it varies as it moves. Now to the question, I've got no idea what it is and whether or not to hook it out at some point in the not too distant future. As I don't know what it is could it be one of these things that turns it's stomach inside out and poisons eveything else in the process. Am I right in having the attitude to leave things alone to get on with life or do I consider this fella and hitchhikers in general a threat? We have a few small fish, a couple of crabs, and about 10 corals and I'm concerned that something is going to start munching on them.

What do you guys reckon?

Cheers

 

[idlefingers]

Sounds like Somatella varia to me.. completely harmless algae grazer. Here's a quote from reefkeeping.com about them:

Almost slug-like, but possessing an auriform, cap-like shell, individuals of Stomatella seem unlikely to be Trochoideans. However odd their appearance, their internal anatomy puts them squarely in this group. Stomatella individuals may reach lengths of about an inch and a quarter (3 cm), and as their specific name of "varia" implies, they may be almost any color, although gray, black, and mottled colors tend to predominate. They are quite good grazers, and also reproduce well in aquaria lacking hermit crabs and shrimp predators. Their shell shape precludes their retraction into the shell, but evolution has given them a rather neat way to escape many predators. The rear portion of their foot can break off, much like some lizards' tails, when they are threatened by a predator. The detached portion then writhes, and twists and otherwise distracts the predator while the snail, presumably, makes good its escape. Additionally, they also tend to be nocturnal and avoid a lot of visually-oriented predators in this way.

Also, here's a link to a thread I started a few months back asking a similar ID question about them.

With regards to what stance to take on hitchhikers, I say take 'em one at a time and try to get a positive ID to decide whether it's safe or not. I wouldn't consider hitchhikers in general as a threat because there's an equally large number of useful hitchhikers.. Just be wary with them (and if you think they're bad and can catch them, get it into a container temporarily) and get an ID on it to figure out whether to leave it (or re-release it if you caught it) or remove it.

 

[1entra]

Check this Hitchhikers link out, I found it quite usefull to help I.D a lot of stuff that appeared on my LR

 

[rabidric]

Yep that somatella varia devil is the one. Looked it up and there it was just like in the tank.

Cheers

 

[SkiFletch]

The most-common "bad" hitchikers that I see a lot IMO are:

Rock/Gorilla crabs which can/do prey on fish/inverts as they get older
Aiptasia anemones whose stings are powerful and with exponential growth rates can quickly over-run a tank
Mojano anemones, same problems as aiptasia
Nudibranchs/sundial snails/"redbugs" which can harm specific coral species. Luckily (with the exception of Sundials) most of these pests die without a host in the couple months or so before the aquarist begins stocking corals

 

[Musho3210]

flatworms are pretty annoying, as well as colonial hydroids.

 

[SkiFletch]

True, not the most common IME though

 

[rabidric]

Thanks guys. We've had a few nudibranches as we've added bits of live rock to the original heap. They're fairly easy to catch with a long pair of tweezers and as they seem to attach themselves to the tank walls they're easy to remove. I'm just conscious that there's probably more beasts roaming the tank unseen than seen. For instance we have a blennie who developed a hole in his gill cover which, having shown pictures around at the LFS, it was decided was where he'd been bitten or pinched. Now we don't have anything known in the tank that could do that, so I wonder what might have done it and hence my concern over hitchhikers in general.

Oh well, I'm sure there will be more unknown lovelies making themselves known so I'll keep watching and maybe asking for guidance although the sites mentioned should spare you from too many questions.

Thanks again

R