Barnacles are often overlooked but a short trip into the life of these varied and advanced creatures tells a different story.
A barnacle is a type of arthropod in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters. They are sessile suspension feeders, and have two larval stages.
Free-living barnacles are attached to the substratum by cement glands that form from the base of the first pair of antennae; in effect, the animal is fixed upside down by means of its forehead. In some barnacles, the cement glands are fixed to a long muscular stalk, but in most they are part of a flat membrane or calcified plate.
Barnacles are displaced by limpets and mussels, who compete for space. They also have numerous predators. They employ two strategies to overwhelm their competitors: "swamping" and fast growth. In the swamping strategy, vast numbers of barnacles settle in the same place at once, covering a large patch of substrate, allowing at least some to survive in the balance of probabilities.
Most barnacles are hermaphroditic, The ovaries are located in the base or stalk, and may extend into the mantle, while the testes are towards the back of the head, often extending into the thorax.
The sessile lifestyle of barnacles makes sexual reproduction difficult, as the organisms cannot leave their shells to mate. To facilitate genetic transfer between isolated individuals, barnacles have extraordinarily long penises. Barnacles have the largest penis to body size ratio of the animal kingdom.
Yellow-rimmed goose barnacles , also called stalked barnacles, filter-feeding crustaceans that live attached to hard surfaces of flotsam. A medieval myth was these barnacles grew into Barnacle Geese, in the days before it was realised that birds migrate, it was thought that Barnacle Geese, Branta leucopsis, developed from this crustacean, since they were never seen to nest in temperate Europe, hence the scientific and English names. The confusion was prompted by the similarities in colour and shape. Because they were often found on driftwood, it was assumed that the barnacles were attached to branches before they fell in the water.
The buoy barnacle Dosima fascicularis, , is "the most specialised pleustonic goose barnacle" species. It hangs downwards from the water surface, held up by a float of its own construction, and is carried along by ocean currents.
Whale barnacles are barnacles belonging to the family Coronulidae. Whale barnacles attach themselves to the bodies of baleen whales during the barnacles's free-swimming larval stage. Though often described as parasites, the relationship is an example of obligate commensalism, as the barnacles neither harm, nor benefit, their host.