Sur le tunicier pélagique Doliolum Nationalis Borgert 1893 en méditerranée occidentale (campagne du «president-Theodore-Tissier» septembre-octobre 1958)

Examining the planktonic material collected by the oceanographic vessel of the Institute of Marine Fisheries the "Président Théodore-Tissier", in autumn 1958, in the western Mediterranean area located north of the 42nd parallel, some samples proved to be very interesting in the study of individuals budded by Doliolum nationalis phorozoids, recently characterised by a member of our team. This pelagic tunicate abounds in the area, and contrary to what is usually observed in the Mediterranean Sea or the Atlantic Ocean, for this species, embodied only by phorozoids, two stages-a phorozoid stage and a (apparently) gonozoid stage-meet together. But these gonozoids are aberrant: they have both well-shaped gonads and a ventral peduncle with buds, a typical characteristic of phorozoids which confirms the common origin of the two individuals, also budded by phorozoids in a short cycle which would superimpose on a normal cycle rarely followed by the species (BRACONNOT, 1967). These observations drove us to consider a morphological study of these "gonozoids" of a new type as well as the distribution of both stages.