LAMINATED STRUCTURE IN THE GOBY TELENCEPHALON RESEMBLES IN ITS CYTOARCHITECTURE THE MAMMALIAN HIPPOCAMPUS

The development of the telencephalon in ray-finned fish differs from that of all other vertebrates in that it is formed through the process of eversion, resulting in two solid hemispheres separated by a common ventricle. This developmental process is believed to be responsible for the formation of a non-laminar telencephalon. Accordingly, ray-finned fish do not have a layered cortex and do not exhibit gyrification. Their telencephalon can be divided into an area dorsalis (D) and an area ventralis (V), which are considered equivalent to the pallium and subpallium. The telencephalic areas are organised in nuclei, named according to their location. Hence, layered structures are not present in the telencephalon. The order of gobies (Gobiiformes) is an exception here: A novel multilayered structure can be identified in the posterior region of the dorsal area. Visually, this area can be compared to the mammalian hippocampus. It consists of up to four subregions surrounded by rows of cells. Using Nissl staining, approximately 70 goby species from six families were examined and compared with around 200 ray-finned fish species. This multilayered structure could only be detected in four goby families, which in turn show histological differences. All species examined in these families displayed this structure regardless of their lifestyle. However, this area in not present in the basal goby families. The multilayered cytoarchitecture of this structure is unique among ray-finned fish to date. Its function and origin has not yet been investigated in depth, but it is likely involved in visual information processing.