Staghorn Hydrocoral, Janaria mirabilis

Staghorn Hydrocoral, Janaria mirabilis. Provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, July 2011. Size: 5.0 cm (2.0 inches).

Phylogeny: The Staghorn Hydrocoral, Janaria mirablis (Stechow, 1921),  is a member of the Hydractiniidae Family of Hydrocorals. The genus Janaria is one of sixteen genera in this family. This is the only species in this genus. They are also known as the Staghorn Hermit’s Shell and in Mexico as Hidrocoral Cuernos de Venado.

Morphology:  Staghorn Hydrocoral polyps have radial symmetry, a hollow digestive cavity, and specialized stinging structures in tentacles surrounding the mouth. Their polyps have a flower-like appearance and produce a hard, calcareous skeleton. They live in tightly packed colonies. Because hydrocorals grow so slowly, they do not contribute significantly to reef building. Staghorn Hydrocorals have several vertical branches and a basal, horizontal branch. Most of the vertical branches are similar in height and structure. The branches may be arranged in a plane, like a glove, or three dimensionally, like the prongs of a crown. The author Julia Whitty describes this species as a “fuzzy glove of feeding polyps”. Living specimens are cream to beige in color. They reach 5.0 cm (2.0 inches) in height.

Habitat and Distribution:  Staghorn Hydrocorals are found attached to hermit crab shells and rocks or within sand at depths between 3 m (10 feet) and 183 m (600 feet). They are a tropical Eastern Pacific Species that are found in Mexican waters of the Pacific Ocean from Punta Tosca, Baja California Sur, south to Guatemala. They are found throughout the Sea of Cortez.

Diet:  Staghorn Hydrocorals are suspension feeders, using their tentacles to capture amphipods and other plankton from the surrounding water. The tentacles then pass the food to the mouth.

Predation:  Staghorn Hydrocorals are a poorly studied and understood species. There is very limited documentation regarding their predation. Other hydrocoral species are prey for fish, crabs, gastropods, starfish, and polychaetae worms.

Reproduction: Staghorn Hydrocoral colonies are either male or female. Each has specialized sexual polyps that produce eggs or sperm. Sexual reproduction occurs through broadcast spawning, with internal fertilization. The zygote develops into a planular larva inside the gonophore. When the planula contacts a shell occupied by a hermit crab, it metamorphoses into a founder polyp. The founder polyp then reproduces asexually by budding. These buds eventually break away as a genetic clone of the founder.

Ecosystem Interactions: Staghorn Hydrocorals have a symbiotic relationship with the Staghorn Hermit Crab, Manucomplanus varians and the Deer Horn Hermit Crab, Manucomplanus cervicornis. The hydrocoral begins to encrust the snail shell occupied by the hermit crab. Eventually, the hydrocoral chemically dissolves the shell and the hermit crab is then housed inside the coral colony. The crab is protected by the nematocysts of the hydrocoral and the hydrocoral benefits by the hermit crab moving to new food sources. As necessary, the crab trims the hydrocoral’s growth from around his shell opening.

Human Interactions:  Staghorn Hydrocorals have no direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms:  None