sessile barnacle

A sessile barnacle is a type of barnacle that attaches directly to a surface, such as rocks or pilings, with its calcareous shell. Barnacles are marine crustaceans that are highly adapted for a sedentary life.12

Adult barnacles are covered in plates and cemented head-down to substrates. They filter food particles from the water using feathery appendages called cirri. Most barnacles are hermaphrodites, possessing both male and female reproductive organs, and typically engage in cross-fertilization. Their life cycle begins as free-swimming larvae called nauplii, which eventually develop into a cyprid larva. This cyprid larva then settles on a surface and undergoes a dramatic metamorphosis into a juvenile barnacle, permanently fixing its location. Sessile barnacles include acorn barnacles, which have a conical shell made of calcareous plates.234