Willow leaf larva
Willow leaf larva or Leptocephalus is the name given to the flat and transparent larva of eel-like fish and all other Elopomorpha . After the larval period, the so-called glass eel develops from it in the course of migration . The German name alludes to the willow leaf- like appearance.
This larva was originally described as a separate species of fish called Leptocephalus .
As early as 1886, Yves Marie Delage (1854–1920) showed in the station biologique de Roscoff that the "species" Leptocephalus morisii were young conger eels ( Conger conger , Linnaeus , 1758). (The willow leaf larva was previously assessed as the larva of e.g. moray eels .)
From 1887 the Italian zoology professor Giovanni Batista Grassi and his colleague Calandruccio investigated leptocephali in the Mediterranean. In 1894 they published the result of their investigations, namely that the alleged species Leptocephalus brevirostris is actually the larva of the European eel.
In the case of the European eel ( Anguilla anguilla ), this larval period lasts about three years and is lived through in the Atlantic ; as a glass eel, it then migrates into the rivers of western Europe.
Phylogenetically , this form of larvae is also interesting insofar as it can be deduced from it that the ancestors of the eels were not yet so snake-like in body structure (application of the basic biogenetic rule according to E. Haeckel).