Haliotis rufescens Swainson, 1822 - red abalone with encrusting barnacles from California, USA (BMSM 2061, Bailey-Matthews Shell Museum, Sanibel Island, Florida, USA).

The gastropods (snails & slugs) are a group of molluscs that occupy marine, freshwater, and terrestrial environments. Most gastropods have a calcareous external shell (the snails). Some lack a shell completely, or have reduced internal shells (the slugs & sea slugs & pteropods). Most members of the Gastropoda are marine. Most marine snails are herbivores (algae grazers) or predators/carnivores.

The abalones are an odd group of gastropods that have a coiled, cap-shaped, aragonite shell with a curvilinear set of excurrent respiratory holes. Interior shell surfaces have intensely iridescent nacreous aragonite ("mother of pearl"). Abalones are hard substrate algae grazers.

From museum signage [typos and mis-spellings corrected]: "Abalones are gastropod molluscs that typically have a widely open shell with holes. The holes serve to expel water after it circulates through the animal during breathing. Some abalones have very elegant shapes and striking colors and their beauty is boosted by the presence of a colorful layer of mother-of-pearl lining the interior of the shell."

"There are about 75 species of abalone. These species live on submerged rocks along different continents and islands, usually in cold water areas The West Coast of the U.S. is rich in abalone species. Abalones attach themselves to the rocks using a powerful shell muscle. They are herbivores, grazing on seaweed, with help from a set of specialized teeth called a radula."

The whitish structures attached to the abalone shell shown above are barnacles (Animalia, Arthropoda, Crustacea, Cirripedia). Barnacles are sessile, benthic, filter-feeding crustaceans. They are hard-substrate encrusters and can be found attached to rocks, shells, skeletons, or wood. Barnacles can also be found attached to the skin of large marine mammals such as whales and manatees. The barnacle skeleton is usually shaped like a cinder cone volcano and typically consists of overlapping calcareous plates. They are common in rocky shore intertidal zone environments and can tolerate subaerial exposure during high tide, but have to be water occasionally. When submerged by seawater, the filter feeding apparatus emerges, which consists of several limbs that have been evolutionarily modified into feathery appendages.

Classification: Animalia, Mollusca, Gastropoda, Haliotidae

Locality: unrecorded locality in California, USA

More info. at: en.wikipedia.org/wiki/Haliotis and en.wikipedia.org/wiki/Haliotis_rufescens and