#actinosphaerium

"If a heliozoan's axopodia seem threatening to you, that's good. Those stiff spikes aren't there as decoration, they play an important role in the heliozoan's hunt for food, whether that's other protists or even tiny animals. You should probably think of them less as spikes and more as sticky skewers. After the heliozoan's prey get caught in the axopodia, it is immediately immobilized and stuck to the adhesive surface. The prey then gets drawn in towards the heliozoan itself until it is close enough to be engulfed into a vacuole for further digestion."

Journey to the Microcosmos- Heliozoa: Round, Sticky, and Covered in Spikes

"These experiments were not the end of the "poke and prod and disrupt the axopodia" approach to heliozoan research. A later study would use what feels almost a poetic method--or at least a poetic as you can get a science experiment and a microbe names after a sun god. The researchers subjected their heliozoan to ultraviolet light, watching as the ends of the axopodia broke down and shortened, or sometimes even broke off altogether. Yet, even then, when the ultraviolet light had passed, the sun animalcule's microtubules were ready to grow once more."

Journey to the Microcosmos- Heliozoa: Round, Sticky, and Covered in Spikes

"While axopodia are, in a sense, the cytoplasm poking outwards, there needs to be something underlying those extensions to give them shape and structure. That "something" are hallow filaments called microtubules. Made from a protein tubulin, you can think of microtubules as building blocks for eukaryotic cells, though they're shaped like rods, not actually blocks. Microtubules show up in mitotic spindles, cilia, flagella, and many other pieces of cellular machinery. How they're arranged inside an organism--whether they are unicellular or multicellular--impacts everything from shape to movement. Heliozoa's axopodia are no different."

Journey to the Microcosmos- Heliozoa: Round, Sticky, and Covered in Spikes

Images Originally Captured by Jam's Germs

"After all, axopodia have quite a lot to do. They're not simply stagnant spikes on a heliozoan. They're an extension of the organism's cytoplasm, carry the extrusomes that make their surface adhesive. They contract when the organism needs them to, like when they're drawing in their prey. It's tempting to compare the axopodia to having just a bunch of arms, but the comparison doesn't do the axopodia justice. After all, it's not like we can retract and extend our arms out of our bodies at will."

Journey to the Microcosmos- Heliozoa: Round, Sticky, and Covered in Spikes

"In the 19th century, when heliozoa were first described, the label was thought to apply to just about any spiky, freshwater organisms that looked like spiky, freshwater organisms. The similarity in their appearance suggested a proximity in their categorization, so it made sense to group them together. That has of course changed in more recent years as scientists have turned to studies of organisms' DNA to revise those early classification systems so they better match genetic relationships. Today, "heliozoa" is less of a specific label and more of a description, referring to a set of organisms that are round with stiff pseudopodia or anopodia, the more technical term for those spikes. They are not necessarily closely related to one another, they just look like it."

Journey to the Microcosmos- Heliozoa: Round, Sticky, and Covered in Spikes

"The central, driving life of the heliozoan is in that central body, where food is consumed and the important biological molecules that keep the organism alive are made. What a fine, spherical body it is. But let's be honest: it's the axopodia that makes a heliozoa so striking to lood at. For as long as we've been looking at heliozoa, we have wanted to know more about how those axopodia work and how they're made."

Journey to the Microcosmos- Heliozoa: Round, Sticky, and Covered in Spikes

Images Originally Captured by Jam's Germs