Barnacles: favoured by Darwin, convergent by nature

Haeckel_CirripediaTo mark Darwin Day 2015, which falls around Charles Darwin’s birthday (12th February) each year, we’re flagging up a marvellous creature that he particularly admired for its many strange characteristics: the barnacle. Naturally, the barnacle shows a host of notable convergences!

Although they hardly resemble lobsters or shrimps, barnacles are in fact crustaceans and belong to the group ‘Cirripedia’. These peculiar crustaceans are justly famous for the scrutiny they received from Charles Darwin and here are just a few cases of convergent evolution found among barnacles:

  • Independent reduction in the number of shell plates
  • Convergence of shell plate material, which is phosphatic rather than the typical calcareous composition, with lamellar bone structure.
  • Reduction of the abdomen (posterior region) of the barnacle body to a vestigial state by the same genetic regulatory changes that underly loss of abdomen segments in other arthropods, for example in the mites Tetranychus urticae and Archegozetes longesitosus.

For more on convergent evolution in this and other crustaceans, head over to explore crustacean convergence at the Map of Life.

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