These giant prehistoric fish are capable of swallowing prey of medium size or smaller whole with a natural 20 on the attack die, and creatures who are swallowed suffer an additional 2d4 points of damage automatically each round from acid (most will die of this long before suffocation becomes an issue). Only the smallest weapons (such as daggers, for example) can be used by a swallowed creature, but on the other hand a dinichthys has an armor class of just 11 on the inside.