A group of marine worms (nemerteans) that lack a proboscis sheath or armor-like structures, representing the most primitive lineage of ribbon worms.
From Ancient Greek 'an-' (without) + 'hopla' (arms, weapons, armor). The term was coined in the 19th century to classify nemertean worms based on their lack of specialized defensive structures compared to other ribbon worm groups.
These 'unarmed' worms might sound defenseless, but they're actually successful survivors—they've existed relatively unchanged for hundreds of millions of years, suggesting their simple design is perfectly efficient for deep ocean life.
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