Millet butterflyfish stripe runs from above the eye to the base of the operculum, and there is a large black patch on the caudal peduncle. This fish is endemic to the Hawaiian Islands and the Johnston Atoll, and is found down to depths of at least . Its habitats include coastal fringing reefs, outer reefs and lagoons. The millet butterflyfish is a schooling species found in mid-water that feeds on zooplankton. It also feeds opportunistically on polychaete worms and other small invertebrates on the seabed. Food is drawn into the mouth by rapid suction. It does not seem to be territorial but
Operculum (gastropod) to push into the substrate in a leaping form of locomotion. Virtually all pulmonate snails are inoperculate, i.e. they do not have an operculum, with the exception of the Amphiboloidea. However, some terrestrial pulmonate species are capable of secreting an epiphragm, a temporary structure that can in some cases serve some of the same functions as an operculum. The epiphragm may be distinguished from the true operculum by its homogeneity and want of growth marks. In ammonites (extinct shelled cephalopods), a calcareous structure known as the aptychus (plural aptychi) existed. When these were first described they were thought to be