Hydrolagus

Hydrolagus is a genus of cartilaginous fish belonging to the family Chimaeridae. These fish are commonly known as chimaeras or ghost sharks. They are characterized by their large heads, tapering bodies, and long, whip-like tails. Hydrolagus species possess a single, venomous spine in front of their dorsal fin, used for defense. Their eyes are large and often luminous, adapted for life in deep, dark waters.

Chimaeras are found in oceans worldwide, inhabiting depths from the continental shelf to the deep sea. They are typically solitary and elusive, making them difficult to study. Their diet consists mainly of small invertebrates, crustaceans, and fish, which they crush with their flattened, tooth-like plates. Hydrolagus reproduction is oviparous, with females laying large, spindle-shaped egg cases.

The genus Hydrolagus contains numerous species, each with specific geographical distributions and slight morphological differences. Examples include Hydrolagus colliei, the spotted ratfish, found off the Pacific coast of North America, and Hydrolagus mirabilis, the abyssal chimaera, inhabiting deeper waters. Despite their ancient lineage, chimaeras are poorly understood, and much of their biology remains a mystery. Conservation status varies among species, with some facing threats from overfishing and habitat degradation.