Is That a Starfish in your Filter…

… or are you just happy to see me?

A couple of weeks ago I noticed one of my aquarium filters running strangely slowly. The suction seemed much lower than normal and the motor seemed to be struggling. This happens occasionally when algae buildup (or live sponges) inside the intake starts to block the flow. As usual, I turned off the filters and took the screen off the intake, preparing to clean the assembly  – and a dozen of these crawled out:

For the unfamiliar, the filter-blocking ninjas are “micro-brittle stars,” small detritus-eating echinoderms related to “regular” starfish. I knew I had them in my tank – in fact, I previously blogged a video of one that (unusually) went walkabouts in daylight.

Most of the time micro brittles spend daylight hours hidden, though they wave their arms in the current when they sense food in the water.

When I removed the filter cap, I discovered seven more micro brittles clinging happily to the inside of the filter intake with their mouths directed into the current. Their positioning and swollen bodies explained exactly why the filter slowed.

They were blocking the flow, mouths open to capture anything that the filter pulled in past them.

The expression “drink from the fire hose” comes to mind.

I gently removed them from the filter and returned them to the tank. Most of them crawled away as fast as their bristly legs could carry them, but the two largest seemed content to crawl around on my hand for several minutes, giving me the opportunity to take the photos that appear in this post.

So … what’s the strangest thing you’ve ever discovered living in a place you didn’t expect?