Barnacles

Description:

Crustaceans which as adults have a calcified exoskeleton comprised of several chalky plates, forming a shell. Sessile with a shell slightly asimetrical, up to 1,2cm in diameter with 6 grooved plates arranged as a cone. Lateral plates overlap terminal plates so that these appear narrow. This specieis hás an oval opening. Colour usually whitish. Effectively they are attached to the rocks by their head ends, and their thoracic appendages have became modified as filter- feeding organs. These can be projected outside the shell and swept backwards and fowards through the water to collect any appropriate food particles.

Habitat:

On rocks on upper and middle shore. Range dependent on exposure, always found above Semibalanus balanoides on the shore. Distribution Mediterranean, Atlantic and English Channel.

Notes:

The sexes of barnacles are separate, males having proportionately probably the largest penis in the animal kingdom. It reaches out of the shell and transfers its sperm to a female neighbour. After fertilisation the female barnacle broods its eggs until they hatch as a minute nauplius larva which swims until it transforms to another larval stage called a cypris that then settles head-down on a suitable surface.