If you have ever wandered along the coast, you may notice tiny little bumps covering rocks. It is most likely that these are barnacles. Many people can recognize barnacles, but may actually know very little about them. The first thing to realize is that barnacles are actually crustaceans, not molluscs as many people think. They are most closely related to other crustaceans such as crabs and lobsters.
To give you an idea, here is a picture of an aggregation of the barnacle Balanus glandula accompanied by a diagram of basic barnacle anatomy:
You may notice that in the anatomical diagram above the feeding appendages are called feeding “legs”. In fact, the cement gland seen in the diagram above, which attaches the barnacles to the substrate, is very close to their antennae. So it is almost as if barnacles stand on their head and wave their feet above them.
You may also notice the barnacle has both eggs and a testis. They are hermaphroditic and thus have both male and female reproductive organs. However, they do still reproduce sexually with other barnacles.
Another interesting aspect of barnacles is their lifecycle. Barnacles have two main life stages: the sessile adult stage and the planktonic larval stage. The sessile adult stage was introduced above, but the planktonic larval stage is the stage at which barnacles are mobile.
Plankton, coming from the greek word planktos, which means wanderer or drifter, which is literally what the planktonic barnacle larvae do until they settle. Here is a video of what the nauplii larvae of barnacles look like, notice that at this life stage the barnacles actually look a bit like other crustaceans:
Barnacles do not necessarily need to attach themselves to rocks, barnacles can be found attached to many other objects. Check out earlier blogs for information on fouling communities, where barnacles can often be found!
Barnacles may even settle on other animals! This is beneficial to them because settling on a whale that likes to swim through plankton clouds for it’s own food, gives the barnacles plenty of opportunity to feed on the plankton themselves.
If you are open to a more ambitious read, check out this paper on how barnacles settle on whales:
Barnacles feed by waving their feeding appendages, called cirri, in the water and collecting the plankton down into their mouth. Here is a video of how barnacle’s feed:
The feeding appendages of barnacles can actually be quite beautiful:
What seemed like a very simple organism is actually pretty cool isn’t it?
For more information on barnacles, check out the links below: