Re:Critters in my Tank

Pete Giwojna

Dear MySanity:

It’s very difficult to say what they little shell-less snails or slugs you noticed may actually be without seeing them. However, if they are all crawling on the glass and the live rock rather than swimming in the water or clinging to the seahorses, then my best guess is that they are probably harmless (possibly some type of flatworm) rather than a parasite of some sort. But that’s merely a guess and you should try to identify the worms more accurately in order to determine their true nature.

The appearance of various invertebrates and microfauna such as this in a marine aquarium is the very reason aquarists refer to the live sand and live rock in their tanks as "live." It can be very difficult to accurately identify all of the mysterious life forms that may blossom from your live rock over the months and years, but 99% of them are harmless, benign, or beneficial to the aquarium and the pageant of life that appears in microcosm from the LR is fascinating to observe 100% of the time.

Reef Central ( is the place to go to identify all of the interesting critters that pop up from live rock or live sand or natural seawater. They have an excellent series of photo galleries on their site, including one devoted to Reef Tank Hitchhikers, so you might check in there and see if any of their photos look like the tiny translucent slugs you are concerned about:

Click here: Reef Central Online Community

Reef Central has a discussion forum devoted just to seahorses, so it’s a good place to visit from time to time anyway.

Also, if you copy and paste the following URL into the Web browser on your computer, it will take you to another site with lots of photographs of aquariums hitchhikers that may help you to identify your mystery critters:

Finally, MySanity, if you go to and look in the photo galleries in the "Fauna" section, that’s another good way to identify the hitchhikers and mysterious invertebrates that appear seemingly out of nowhere in a dynamic marine aquarium:

Let me know if you find any photos that look like your tiny slugs and can verify their identification, MySanity, and I will be happy to advise you whether they are harmless or should be removed from the aquarium. In the meantime, as long as they are ignoring your seahorses and vice versa, I don’t think there’s any danger to the ponies.

Best of luck identifying your mystery critters!

Pete Giwojna

America's Only Seahorse Aqua-Farm and One of Hawaii's Most Popular Attractions

Ocean Rider seahorse farm is a consistent Trip Advisor Certificate of Excellence Award Winner and "Top 10 Things To Do" Kona, Hawaii attraction. Our "Magical Seahorse Tours" are educational and fun for the whole family.

Tour tickets are available for Purchase On-Line. Space is limited and subject to availability.

small seahorse Ocean Rider, Inc. is an Organic Hawaiian-Based Seahorse Aqua-Farm & Aquarium that Follows Strict Good Farming Practices in Raising Seahorses and Other Aquatic Life.

Seahorse Hawaii Foundation

Inspiring ocean awareness by saving the endangered seahorse and sea dragons around the world from extinction through conservation, research, propagation, and education.

Help us save the seahorse and the coral reefs they live in with a tax deductible contribution to the Seahorse Hawaii Foundation. You will be helping to protect and propagate over 25 species of endangered seahorses, sea dragons and friends.

Make A Tax-Deductible Donation Today!

A Different Kind of Farm (Video) »

Ocean Rider Kona Hawaii

Ocean Rider Kona Hawaii
Seahorse Aqua-Farm & Tours

73-4388 Ilikai Place

Kailua Kona, Hawaii 96740

Map & Directions


Contact Ocean Rider

Copyright ©1999-2023
All Rights Reserved | Ocean Rider Inc.

My Online Order Details

Purchase Policy

Site Terms and Conditions