Ectopic presence of saccus vasculosus tissue in the neurohypophysis of three species of plectognath fishes (Tetraodontiformes, Teleostei).

The extraregional occurrence of saccus vasculosus tissue was observed in the neurohypophysis of several specimens of three species of plectognath fishes, Fugu niphobles. Fugu poecilonotus and Canthidermis rotundatus. The ectopic tissue occurred as a compact multitubular structure in the posterior portion of the pars nervosa, either being buried in it or attaching to its dorsal margin. Scanning electron microscopy revealed that ectopic crown cells of F. niphobles were distributed further in the ependymal layer of the infundibulum. A possible route of these crown cells to the neurohypophysis was discussed with special reference to the close anatomical relationship between the neurohypophysis and the saccus vasculosus in the embryonic stage.