Everything about Cirripedia totally explained
The cyprid stage lasts from days to weeks. During this part of the life cycle, the barnacle searches for a place to settle. It explores potential surfaces with modified
antennules structures; once it has found a potentially suitable spot, it attaches head-first using its antennules, and a secreted glycoproteinous substance. Larvae are thought to assess surfaces based upon their surface texture, chemistry, relative wettability, colour and the presence/absence and composition of a surface biofilm; swarming species are also more likely to attach near to other barnacles. As the larva exhausts its finite energy reserves, so it becomes less picky in the sites it selects. If the spot is to its liking, it cementing down permanently with another proteinacous compound. This accomplished, it undergoes
metamorphosis into a juvenile barnacle.
Adult stage
Typical
acorn barnacles develop six hard calcareous
plates to surround and protect their bodies. For the rest of their lives they're cemented to the ground, using their feathery legs (cirri) to capture plankton.
Once metamorphosis is over and they've reached their adult form, barnacles will continue to grow by adding new material to their heavily calcified plates. These plates are not
moulted; however, like all
ecdysozoans, the barnacle itself will still molt its
cuticle.
Sexual reproduction
Most barnacles are
hermaphroditic, although a few species are
gonochoric or
androdioecious. Typically, recently molted hermaphroditic individuals are receptive as females. Self-fertilization, although theoretically possible, has been experimentally shown to be rare in barnacles .
The sessile lifestyle of barnacles makes
sexual reproduction difficult, as the organisms can't leave their shells to mate. To facilitate genetic transfer between isolated individuals, barnacles have extraordinarily long
penises, up to 15cm in length: the largest penis to body size ratio of the animal kingdom.
Fossil record
The geological history of barnacles can be traced back to the early Palaeozoic (in the order of 4-500 million years ago), although they don't become common in the fossil record until the
Neogene (last 20 million years). In part their poor preservation is due to their restriction to high-energy environments, which tend to be
erosional - therefore it's more common for their shells to be ground up by wave action than for them to reach a depositional setting. It is also possible that the group was more minor in the past.
Barnacles can play an important role in estimating palæo-water depths. The degree of disarticluation of fossils suggests the distance they've been transported, and since many species have narrow ranges of water depths, it can be assumed that the animals lived in shallow water and broke up as they were washed down-slope. The completeness of fossils, and nature of damage, can thus be used to constrain the tectonic history of regions..
Barnacles are of economic consequence as they often attach themselves to man-made structures, sometimes to the structure's detriment. Particularly in the case of ships, they're classified as
fouling organisms.
Some barnacles are edible by humans, and
goose barnacles (
for example Pollicipes polymerus) are treasured as a delicacy in many Mediterranean countries. The resemblance of this barnacle's fleshy stalk to a goose's neck gave rise in ancient times to the notion that geese, or at least certain seagoing species of wild goose, literally grew from the barnacle. Most notably, the wild
Barnacle Goose (
Branta leucopsis), whose eggs and young were rarely seen by humans because it breeds in the remote
Arctic, got its popular name because it was imagined to grow from gooseneck barnacles.
Classification
Some authorities regard Cirripedia as a full
class or
subclass, and the orders listed above are sometimes treated as
superorders.
This article follows Martin and Davis in placing Cirripedia as an infraclass of
Thecostraca and in the following classification of cirripedes down to the level of orders :
Infraclass
Cirripedia Burmeister, 1834
Further Information
Get more info on 'Cirripedia'.
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