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Investigate this strange group of (mostly) shell-bearing crustaceans that are often seen on rocky shores of Queensland.
Barnacles belong to a group of highly specialised crustaceans called the Cirripedia. Many people still assume barnacles are related to molluscs, but inside the interlocking shell plates is an animal similar to an upside-down shrimp. While adults are strange in appearance, and mystified naturalists for many years, barnacle eggs hatch into unmistakable crustacean larvae. Barnacles mostly feed on suspended particles in the water by opening the top plates of the shell and protruding their feathery legs (cirri), which trap microorganisms from the water flowing past.
While most species live attached to inanimate hard substrates, some attach to other living objects, and can actually be embedded in sponge, sea-fan and coral hosts, and even bury into the flesh of whales and turtles. One extraordinary group, the Rhizocephala, live as internal parasites of crabs.
Seventy-three barnacle species have so far been found in south-eastern Queensland. Commonly-encountered species include:
Although barnacles resemble hard-shelled molluscs, they are shrimp-like crustaceans living inside (and attached to) their hard outer casings. When a larval barnacle settles on a substrate, it secretes a cement-like glue to anchor itself, and develops calcified shell plates. The appearance of these plates mystified naturalists for years, and it wasn’t until the 1800s that an army surgeon discovered that barnacles have crustacean larvae.
Barnacles are suspension feeders, and use their legs to capture food particles from the surrounding water. These feather-like legs are what give barnacles their scientific name – Cirripedia, meaning ‘feather foot’.
Yes. Like other crustaceans, they moult, but the process is not clearly visible as it occurs within the surrounding shell plates.
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