Describing a sponge spicule or skeletal element with six rays or points extending in different directions.
From 'hexa-' (six) plus 'actinal' from Greek 'aktis' (ray). This morphological descriptor is used in sponge taxonomy and paleontology.
Picture a starfish made of glass stretched in six directions—that's basically what hexactinal spicules look like under a microscope, and they're one of nature's most elegant geometric structures.
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