Relating to or describing animals that lack a collarbone or clavicle, particularly in scientific or zoological classification.
From Greek 'a-' (not) + 'kleis' (key, from 'kleido-' meaning collarbone), literally 'without a collarbone,' used in zoological taxonomy.
Birds, snakes, and many fish are acleidian — they don't have collarbones, which gives them incredible flexibility; their skeletons reveal evolutionary trade-offs between flexibility and strength.
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