The extracellular morphology and behaviour of the last common ancestor of animals and choanoflagellates

Last common choanoflagellate ancestor likely had an organic, non-silicified extracellular covering with one or more layers and could both swim and crawl.

• Why it matters: Mapping extracellular morphology and behaviors onto choanoflagellate phylogeny is needed to reconstruct how early animal extracellular structures evolved, despite much undescribed diversity and unclear trait–tree links.
• What they did: The study combined super-resolution fluorescence imaging, electron microscopy, and transcriptomic analysis across Craspedida and Acanthoecida using closely related species pairs plus novel isolates from previously unexplored clades.
• The result: Extracellular traits were strongly conserved among close relatives but showed innovations at deeper distances, and early-branching taxa sister to loricates support lorica as a derived, not ancestral, feature.

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