Washington, May 20 : Scientists have got a clue in solving the mystery behind a crustacean that has only been seen in the form of larvae, suggesting that the adult of the species could exist in a parasite form.
Y larvae, or facetotectans, are found amongst marine plankton in oceans from the poles to the tropics.
First identified in 1899, they have been one of the greatest zoological mysteries for over a century, as no one has ever found an adult of these puzzling crustaceans.
Even though they are ubiquitous and similar to the larvae of barnacles, not one adult y-organism has been identified in over 100 years of considerable searching.
Despite the plethora of these larvae in plankton, leading generations of marine zoologists have wondered just what y- larvae grow up to be.
"Facetotectans are the only crustacean group with a taxonomy based solely on larval stages", said Henrik Glenner and Jens Hoeg from the University of Copenhagen and colleagues from Japan. "But, the great species diversity indicates that the adults play an important ecological role."
Now, a study published in the journal BMC Biology has reported that the transformation of the larvae into a previously unseen, wholly un-crustacean-like, parasitic form.
The study authors collected over 40 species of y larvae from one site at Sesoko Island near Okinawa, Japan, and exposed many of them to a crustacean moulting-hormone to encourage them to mature.
The free-swimming y-larvae shed their articulated exoskeleton, and a simple, slug- like, pulsing mass of cells emerged.
According to the authors, "The musculature and compound eyes that you might expect to see in adult crustaceans were in a state of degeneration, and from our observations of the live, and also preserved specimens, we conclude that the adults of these larvae must be parasites - but of what we do not know."
The great diversity of Facetotecta and the finding that they are most likely parasitic as adults hints at a major ecological role that future studies, both in laboratories and in the field will try to uncover.
These findings provide a tantalising glimpse of the solution to this 100-year-old riddle.