Haliclystids

Haliclystids are a family of stalked jellyfish belonging to the class Staurozoa. These unique cnidarians are characterized by their sessile lifestyle, attaching to substrates like seaweed or rocks with an adhesive aboral holdfast. Unlike most jellyfish that drift in the water column, haliclystids remain anchored for most of their adult lives.

Their body plan consists of a stalk and a calyx, which bears eight arm-like appendages. These arms are equipped with clusters of nematocysts, the stinging cells used for capturing prey and defense. The mouth is located on the oral surface, surrounded by these arms. Haliclystids are carnivorous, feeding on small invertebrates such as crustaceans and small fish that come within reach.

Reproduction in haliclystids can involve both sexual and asexual phases. Some species release gametes into the water column for external fertilization, while others brood their eggs or reproduce asexually. The life cycle typically involves a benthic planula larva that settles and develops into a stalked polypoid form, which then matures into the adult medusa. They are found in cold-water marine environments worldwide, preferring shallow coastal areas. Their distinctive appearance and sessile nature set them apart from other jellyfish.