Their bodies are elongated and compressed with greatly depressed heads.

They have long air sacs that serve as lungs that extend from the gill chamber.

Their dorsal fins are short and have no spine.

Their pectoral fins have an associated venom gland, so the fish are considered dangerous.

Up to six species in this genus are recognized:[2][3] FishBase does not list H. fuscus[2] while the Catalog of Fishes considers H. microps a synonym of H.