Sluglike hitchhiker

mellophanic · May 10, 2023

Three of these black sluglike hitchhikers came with a coral I received today. They didn't react to a dip, are slimy, and are not really possible to scrape off.

Closest thing I've found is elephant slug but that doesn't seem to be a perfect match. Also I haven't seen them move, and haven't seen any antenna yet.

Appreciate any potential IDs!

ISpeakForTheSeas · May 10, 2023

From what I can see it could potentially be sponges, flatworms (I'm not super familiar with flatworms yet, so the one that I know of that looks the most like this - Pseudoceros velutinus - comes from the Mediterranean), or headshield slugs (like Nakamigawaia felis and Nakamigawaia spiralis).

I don't see any rhinophores or gill structures, so I wouldn't expect it to be a nudibranch or sea hare.

Sorry I don't know for sure here, but hopefully we can figure this out for you.

Either way, welcome to Reef2Reef!

mellophanic · May 10, 2023

Thanks! And, pseudoceros seems pretty similar, although most photos seem to be of colorful variants.

Hopefully they're reef safe... And also hope that they don't do anything bad if they die without the right food sources.

ISpeakForTheSeas · May 11, 2023

mellophanic said:
Thanks! And, pseudoceros seems pretty similar, although most photos seem to be of colorful variants.

Hopefully they're reef safe... And also hope that they don't do anything bad if they die without the right food sources.

Generally speaking, flatworms are neutral at best, so if these are flatworms, then you probably don't want them in your tank.

When you say they aren't really possible to scrape off, what do you mean/what makes you say that?

mellophanic · May 11, 2023

ISpeakForTheSeas said:
Generally speaking, flatworms are neutral at best, so if these are flatworms, then you probably don't want them in your tank.

When you say they aren't really possible to scrape off, what do you mean/what makes you say that?

I tried prying them off with tweezers and couldn't get underneath. I didn't want to go to a sharper edge in case I'd cut the things open and release something into the water. I could cut up the coral and toss the "slugs", but I was hoping to avoid breaking apart the skeleton. I suppose I could always glue the pieces back together...

Whatever these are also didn't have any reaction to being poked and prodded. A day later and it doesn't seem like they've moved.

I was looking more into sponges, and the cryptic sponge on this person's rock actually does look similar in color/texture https://www.reef2reef.com/threads/cryptic-zone-for-sponges-in-the-sump-refugium.317736/post-4116970 but sponges should be more fragile to being poked and scraped at, I think?