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Induced metamorphosis in crustacean y-larvae: Towards a solution to a 100-year-old riddle

Henrik Glenner1, Jens T Høeg1*, Mark J Grygier2 and Yoshihisa Fujita3

  • * Corresponding author: Jens T Høeg

  • † Equal contributors

Author Affiliations

1 Department of Biology, University of Copenhagen, Universitetsparken, DK-2100 Copenhagen, Denmark

2 Lake Biwa Museum, Oroshimo 1091, Kusatsu, Shiga 525-0001, Japan

3 Department of Chemistry, Biology and Marine Science, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan

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BMC Biology 2008, 6:21  doi:10.1186/1741-7007-6-21

Published: 20 May 2008



The y-larva, a crustacean larval type first identified more than 100 years ago, has been found in marine plankton samples collected in the arctic, temperate and tropical regions of all oceans. The great species diversity found among y-larvae (we have identified more than 40 species at our study site alone) indicates that the adult organism may play a significant ecological role. However, despite intense efforts, the adult y-organism has never been identified, and nothing is therefore known about its biology.


We have successfully and repeatedly induced metamorphosis of y-larvae into a novel, highly reduced juvenile stage by applying the crustacean molting hormone 20-HE. The new stage is slug-like, unsegmented and lacks both limbs and almost all other traits normally characterizing arthropods, but it is capable of vigorous peristaltic motions.


From our observations on live and preserved material we conclude that adult Facetotecta are endoparasitic in still to be identified marine hosts and with a juvenile stage that represents a remarkable convergence to that seen in parasitic barnacles (Crustacea Cirripedia Rhizocephala). From the distribution and abundance of facetotectan y-larvae in the world's oceans we furthermore suggest that these parasites are widespread and could play an important role in the marine environment.