What projectile weapons could a civilization of merfolk build without the use of magic.
closed as too broad by James♦, Aify, JDługosz, Separatrix, Hohmannfan Feb 15 '16 at 17:08
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The problem with most undersea projectiles is that water resistance makes them fairly range-limited - unless, like a torpedo, they have built-in propulsion. Other than that, compressed air or springs can power harpoons (with or without exploding tips) without too much technical know-how. Heck, even an old school crossbow can do the job over a short range.
I don't know what technology level your merfolk have, but I'd suggest harpoon or spear guns based around compressed air.
They could extract weapons/projectiles from these sea creatures :
1 - Poison projectiles :
2 - Electrical projectiles :
3 - Ink projectiles :
4 - Sharp spears :