The optic tectum ofCalamoichthys calabaricus(Polypteriformes) shows a relatively complex vertical stratification, with six main layers and a varied neuronal typology. In particular, pyriform neurons in the well developedstratum griseum periventriculareand some multipolar neurons in thestratum griseum profundumrepresent the efferent elements of the tectum, while the optic and lemniscal inputs to the tectum converge in the plexiform sublayers of thestratum fibrosum et griseum superficiale. In the circuitry of the tectum some modulation is achieved by some of the polymorphic cells of thestratum griseum internumand by the horizontal cells of the outer layers. Notwithstanding some differences with respect to the teleost optic lobe (i.e., the absence of atorus longitudinalis; the lack of astratum fibrosum marginale; the modest size of thestratum fibrosum profundum; the paucity of neurons in thestratum fibrosum et griseum superficiale; and the ill-defined separation of the layers of the afferent and efferent fibers), the optic tectum ofCalamoichthysresembles the mesotectal type characteristic of teleosts, anurans and reptiles. It exhibits higher degree of organization than the optic tectum of the Chondrostei.
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