No abstract

In this study, we assessed the ovary structure and early oogenesis in representatives of Osteoglossomorpha, one of the most basal Teleostei groups. We aimed to perform a comparative analysis between internally fertilizing Pantodon buchholzi (Pantodontidae) and externally fertilizing Osteoglossum bicirrhosum (Osteoglossidae), Marcusenius cyprinoides, Brevimyrus niger, Gnathonemus petersii and Mormyrus rume (Mormyridae). Our results indicated differences in ovary structure between P. buchholzi and the externally fertilizing species, as well as a considerable disparity in oocyte organization in all studied species. All species possess ovaries of the cystovarian type. In P. buchholzi, the epithelium lining the lumen was columnar and formed crypts with ciliated and microvillus cells as well as deep invaginations with secretory cells, whereas in the remaining species epithelium was squamous. The organization of oogonia and one‐nucleolus oocytes did not differ between species, there were variations in oocytes at subsequent steps of primary growth, including symmetry/asymmetry of the inner cell structure, differences in Balbiani body formation, presence/absence of zonation of the ooplasm, and differences in the order in which cortical alveoli and oil droplets appeared. These differences may be caused by a long and separate evolution of the families as well as adaptation to insemination in the family Pantodontidae.

The aim of this study was to analyse spermatogenesis in the African butterflyfish, Pantodon buchholzi, using transmission electron microscopy and scanning electron microscopy. P. buchholzi is the most basal teleost that exhibits insemination and produces a highly complex introsperm with the most elongate midpiece known in teleost

During the early stages of oogenesis, the Balbiani body is formed in the primary oocytes. It consists of the Golgi apparatus, endoplasmic reticulum (ER), and numerous mitochondria aggregated with germ plasm, but its form may differ among animals. Hypothetically, during oogenesis oocytes become adapted to future development in two different environments depending on internal or external fertilization. We aimed to investigate, using light and transmission electron microscopy, the development of the Balbiani body during oogenesis in representatives of Osteoglossiformes, one of the most basal Teleostei groups. We analyzed the structure of oogonia and primary oocytes in the internally fertilizing butterflyfish Pantodon buchholzi and the externally fertilizing Osteoglossum bicirrhosum and Arapaima gigas to compare formation of the Balbiani body in relation to modes of fertilization. We demonstrated that the presence of the germ plasm as well as the fusion and fission of mitochondria are the conserved features of the Bb. However, each species exhibited also some peculiar features, including the presence of three types of ooplasm with different electron density and mitochondria‐associated membranes in P. buchholzi; annulate lamellae, complexes of the Golgi apparatus, ER network, and lysosome‐like bodies in O. bicirrhosum; as well as karmellae and whorls formed by the lamellae of the ER in A. gigas. Moreover, the form of the germ plasm observed in close contact with mitochondria differed between osteoglossiforms, with a “net‐like” structure in P. buchholzi, the presence of numerous strings in O. bicirrhosum, and irregular accumulations in A. gigas. These unique features indicate that the extreme diversity of gamete structure observed so far only in the spermatozoa of osteoglossiforms is also characteristic for oocyte development in these basal teleosts. Possible reason of this variability is a period of about 150 million years of independent evolution of the lineages.

Xysticus inornatus L. Koch, 1876 was originally described from a single female specimen from Sydney, Australia. After studying new material from the Australian Capital Territory, Dondale later transferred this species to Diaea and described the previously unknown male. Examination of the specimens studied by Dondale reveal that they belong to a different, and probably undescribed, species of Diaea. Detailed studies of the holotype of Xysticus inornatus and the type material of Diaea megagyna Evans, 1995 reveal that they are synonyms.