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From Ancient Greek ἀκτίς (aktís, ray) + ὀστέον (ostéon, bone).


actinost (plural actinosts)

  1. (ichthyology) A bone at the base of a paired fin (of a fish)
    • 1889, Dr. G. Baur, Journal of morphology, Volume 3‎, On the morphology of ribs and the fate of the actinosts of the median fin in fishes[1]:
      The second well-developed actinost is below the vertebra supporting the subcaudal blood-vessels, but that is not so strong proximally as the first; the ribs are not directed downwards, but backwards, and are entirely separated from each other.