About Catomerus polymerus (Darwin, 1854)
Catomerus is a monotypic genus of intertidal and shallow water acorn barnacle containing the single species Catomerus polymerus. It is found in the warm temperate waters of Australia. The genus and species are very easy to identify by the whorls of small plates that surround the base of its primary shell wall; no other shoreline barnacle species in the Southern Hemisphere has this distinctive feature. This species is considered a relic, because this plate structure is only found in primitive living lineages of acorn barnacles or in older fossil acorn barnacle species. It is unusual for this species to be found in the intertidal zone, because living primitive relic species are most often located in more isolated habitats like deep ocean basins and abyssal hydrothermal vents. The maximum observed geographic range of Catomerus polymerus extends from New South Wales to Western Australia, and also includes Tasmania, where the species mostly lives along the northern coast. Within this total range, populations are not continuous, and their distribution is limited by temperature, preferred substrate, and wave action. C. polymerus will not grow in areas with abundant mussels. It prefers warm temperate seas, breeds mainly during the austral winter at temperatures between 14 °C and 17 °C, and occurs in water depths from the sublittoral zone to the lower eulittoral zone.
