rhinophores

Rhinophores are paired chemosensory organs on the heads of many mollusks, most notably sea slugs such as nudibranchs. They function as the animal’s primary olfactory organs, detecting dissolved chemical cues in the surrounding water, including prey odors, pheromones, and habitat characteristics. In many nudibranchs, the rhinophores project from the anterior head and are club-shaped or lamellate, often with numerous folds to increase surface area. They can be retracted into a protective sheath when threatened.

Anatomically, rhinophores are derived from anterior tentacles and contain sensory epithelium rich in olfactory receptor neurons, supported by accessory cells. Nerve fibers from the rhinophores connect to the central nervous system, allowing the animal to interpret chemical signals. The morphology of rhinophores varies widely among species; some are smooth, others feature elaborate lamellae, and color and translucence can reflect underlying tissues.

Ecologically, rhinophores enable critical behaviors such as locating prey (for example sponges, bryozoans, or hydroids), selecting mates, and navigating complex habitats. Their responses are tuned to specific chemical cues, and sensitivity to these cues can influence feeding and reproductive patterns.

Rhinophore anatomy can reflect developmental and evolutionary differences among opisthobranchs. In many species they are retractable and can regenerate after damage, though rates of regeneration vary. Overall, rhinophores are essential chemosensory organs that help mollusks detect chemical information in marine environments and guide feeding and mating behavior.