Blenniiformes is an order of percomorph fish in the clade Ovalentaria, of which it is the most diverse group. This order contains several well-known fish groups such as blennies and damselfish.

The term is derived from the Latin word blennius, which itself comes from the Ancient Greek word βλεννός (blennos), meaning "mucus" or "slime." This refers to the slimy coating that is often found on the scales of blenny fish.

The earliest known member of this order is the stem group-damselfish Chaychanus from the Early Paleocene of Mexico.

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