Blennioidei

Blennies are a highly diverse group of ray-finned fish. They belong to the suborder Blennioidei within the order Blenniiformes. The name "blenny" comes from the Greek words for mucus or slime. These fish live in many different environments. They inhabit marine salt water and freshwater habitats. They also live in brackish water, where fresh and salt water mix. There are nearly 900 described species within this order. Scientists have identified about 151 different genera.

The physical shape of a blenny is quite distinct. Most are small fish, though some reach 55 cm in length. Many have elongated bodies that look almost like eels. They possess relatively large eyes and large mouths. Their dorsal fins, which are on their backs, are often long and continuous. The pelvic fins are short and slender. These fins are located before the pectoral fins and usually have one embedded spine. Most blennies have rounded tail fins. A unique feature is the presence of cirri. These are elaborate, whisker-like structures found on their blunt heads.

Taxonomy, or the way scientists classify life, has changed for these fish. They were once classified as a suborder of the Perciformes. However, the 5th Edition of Fishes of the World moved them. Now, Blenniiformes is part of the percomorph clade known as Ovalentaria. This clade also includes Cichliformes, Mugiliformes, and Gobiesociformes. The definition of "true blennies" was further refined by Eschmeyer's Catalog of Fishes. This catalog added damselfishes and clingfishes to the Blenniiformes order. This left the suborder Blennioidei to represent the true blennies.

There are six specific families that make up the true blennies. The Blenniidae are known as combtooth blennies. The Chaenopsidae are called pikeblennies, tubeblennies, or flagblennies. The Clinidae include the giant kelpfish. The Dactyloscopidae are known as sand stargazers. The Labrisomidae is another distinct family. Finally, the Tripterygiidae are called threefin blennies. Each of these families has its own unique characteristics within the suborder.

The history of blennies can be traced through the fossil record. The earliest known blennoid fossil is a species called Exallias vectensis. This fossil was found in France and dates to the Early Eocene. While this species is known, skeletal remains are rare in older fossils. Most skeletal remains of blennies only appear in the fossil record during the Miocene.

Blennies use several survival strategies to stay alive in the wild. Many are benthic fish, meaning they live on or near the sea floor. They use cryptic coloration to hide from predators. Some species are reclusive and live in reef crevices or empty mollusc shells. Others burrow into sandy substrates. Some are even called "rock-hoppers" because they leap onto rocks to reach different pools. Some blennies use mimicry to survive. For example, Aspidontus taeniatus mimics the bluestreak cleaner wrasse. This allows the blenny to approach other fish closely. Instead of cleaning them, the blenny takes bites out of the unsuspecting fish.

Only one genus of blenny is truly venomous. This genus is named Meiacanthus. These fish have hollow fangs located on their jaws. They use these fangs to inject venom into others. The venom contains several substances, including neuropeptide Y, phospholipase, and an opioid-like enkephalin. This serves as a powerful defense mechanism.

Blennies are important for studying biogeography, which is how life is distributed across the planet. The Blenniidae and Tripterygiidae families have global distributions. The Clinidae families are mostly found in temperate regions. The other three families are largely Neotropical. Scientists believe certain geological events helped these fish evolve. The formation of the Isthmus of Panama split the Tethys Sea. This event, along with Pliocene warming, likely influenced how blennies spread.