Symbiotic relationships are one of the most interesting parts of this hobby. A coral reef is a battlefield for real estate; however, there are still these amazing pockets of cooperation between completely different animals. Everyone is familiar with clownfish and anemones, and for good reason! This combination is likely responsible–more than anything else–for drawing more people into the hobby. This article looks at some less common partnerships.

Hermit Crabs and Coral

A definite oddball are hermit crabs of the genus Paguritta. When aquarists imagine a hermit crab, it’s typically a crab living in a shell, motoring around the tank looking for algae and bits of food to scavenge. These little guys, however, live in colonies of Astreopora and live their whole lives in their burrow. Having said that, I’ve seen them in other corals when they are collected from different regions. For example, these yellow crabs are from Australia, but I’ve seen blue ones from Fiji that were living in Platygyra.

When these hermit crabs first came onto the reef aquarium scene, there really wasn’t a care guide to use, so we had to try our best to keep them alive. We have found that they mainly filter feed, and they seem to really like small meaty foods such as rotifers. They seem to do better with heavy feeding, but it’s important to not overfeed and pollute the tank, because the food they consume is not likely to be quickly consumed by fish or other inhabitants.

Sexy Shrimp and Mini Carpet Anemone

There are actually many types of shrimp that develop symbiotic relationships with both corals and anemones, but the Sexy Shrimp (Thor amboinensis) are my personal favorites because they are not nearly as reclusive as some of the other inverts. That is actually one of the things that kept some really cool symbiotic relationships off of my list. Boxer Crabs (Lybia tessalata), for example, hold a small anemone in each claw, but these critters often hide so much that I can’t get a shot of them. It’s hard for them to make my favorite list when I never see them!

The other nice thing about the anemone and shrimp pairing is that they are very easy to care for. The anemones themselves are very tough and don’t move around as much as some other types of anemones (such as bubble tips, which are likely to run laps around your tank). The shrimp are active and can take care of themselves, so you don’t have to go out of your way to feed them.

Sexy Shrimp will reside in any number of things, not just carpet anemones.

Bisma Worm Rocks

These feather duster worms, also known as Christmas Tree Worms and generally suggested to be Spirobranchus giganteus, are colorful and grow inside colonies of corals like Porites and other SPS (for example, Cyphastrea). These worms bring a lot of interest and motion to what would otherwise be a motionless coral. As you can probably guess, they are filter feeders. I often get asked if they reproduce and increase in number over time. Unfortunately, I don’t have a good answer. I can tell that the tubes that they grow in lengthen over time, but I can’t tell if the individual count goes up.

Walking Dendros

Sticking with the worm theme, this one is a really subtle oddball. This coral is a walking “Dendro,” and I have to put Dendro in quotes because it’s not a Dendrophyllia at all. It’s actually a photosynthetic coral called a Heteropsammia cochlea. The thing that makes it interesting is that it serves as a host to a peanut worm that lives at its base. Unfortunately, peanut worms are very reclusive and not likely to be openly seen. Despite the worms’ shyness, the interaction with the coral is interesting because it drags the coral around the substrate with it. You can expect this coral to be in a different location on the substrate every day as the peanut worm scoots around.

Although the coral is photosynthetic and can get most of its nutrition from light, the Walking Dendro is a capable predator and can gobble up food if offered either meaty frozen foods or, in this case, coral pellet food.

Yasha Goby and Pistol Shrimp

The last symbiotic relationship on this list is the partnership between the Yasha Goby and the pistol shrimp. I love that the fish acts as a lookout for the shrimp that is nearly blind while the shrimp tends to a burrow it makes for both of them. The shrimp almost always has one antenna on the goby as a means of communication.

I also like how they have matching red and white stripes. Anything that is a striking red and white is not particularly common in this hobby. Off the top of my head, I can only think of two other bright red things–a Peppermint Bodianus Hogfish and a Peppermint Angel–which are almost never seen in the hobby.

At first, these two were very reclusive, but over time the fish came out more and more, and now it spends almost all of its time out. The shrimp isn’t out much, but if you are patient it makes an appearance once in a while.


Symbiotic relationships are one of the most interesting things about the reef-keeping hobby. These are my personal favorite oddball examples. What are yours?

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