Pedunculate Cirripedes of the genus Pollicipes

Pedunculate cirripedes, particularly those found on floating objects washed up on the shore, have long been called goose (or gooseneck) barnacles because of their graceful appearance and the long stalk that resembles the neck of a goose. These barnacles are rarely found growing on fixed intertidal substrata. The only truly intertidal pedunculate cirripedes belong to the genus Pollicipes of which there are three species. Two are found on the west coast of the Americas and the third is European. Very little is known about P. elegans from South America. P. polymerus is found on the Pacific coast of North America extending from 27 degrees N to 64 degrees N. P. pollicipes is less eurythermal than P. polymerus and has rarely been found north of the Atlantic coast of France; the most southerly record is about 15 degrees N. Most of this review concerns P. polymerus and P. pollicipes because of the lack of published work on P. elegans. A general description of the animals, the arrangement of the calcified plates, the muscles and the nervous system have all been considered. The animals favour exposed habitats where there is a backwash from surging waves. The strength of the peduncle and its ability to bring the capitulum and the cirri into the best position is related to the captorial method of feeding. A high haemolymph pressure and the musculature of the peduncle enable it to contract or lengthen according to the environmental conditions. The peduncle plays a viral part in combating the effects of temperature change and desiccation. It provides an additional surface for gaseous exchange, and a substratum for settling cyprids. The size of adults at maturity and their fecundity, spermatogenesis and oogenesis have all been discussed. Fertilization, development of embryos, and sizes of nauplii have been compared for the species. The ultrastructure of the membranes involved in fertilization and development of embryos has been examined. Chemical analyses of bodies, egg lamellae, and calcified structures have been determined. Predation and the effect of pollution have been found to be important. The commercial exploitation of all three species and its future possibilities have been examined.