Giant heliozoan eats rotifer!

Sep 24, 2025 • 10:20 AM UTC

United States

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Microorganisms

Michael Chung

Grad student in (bio)physics at UT Austin! Lover of all things creative, especially science 🔬🧬🧪

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One of the coolest samples yet! For some reason, this sample was chock full of rotifers (genus Colurella?). I’ve never seen this many before (potentially more images in the future of these guys). I noticed that there was a HUGE heliozoan (Actinosphaerium arachnoideum?) hanging out near the bulk of the rotifers. I was just taking a few images of the heliozoan when I noticed one of the rotifers getting dangerously close (darkish, unfocused blob in the lower left of the first image). Then, the blob stopped moving and started getting closer to the heliozoan! So, I dropped my responsibilities (sorry to my PI 😅) and observed what happened over the next hour! The heliozoan caught (impaled) a rotifer on its axopodia (spines built from microtubules)! Over time, the poor rotifer was drawn closer to the body of the heliozoan and it appears (after about 30 minutes or so) it was enveloped in a sort of fluid body which I assume is related to digestion. The rotifer did not appear to be completely internalized. So cool to see! I checked the sample again later and found another giant heliozoan near the rotifers..a new hunting ground! This tiny world always blows my mind.