Scorpion katoikogenic ovariuterus - Much more alike to apoikogenic type than it seemed to be

Scorpions are viviparous matrotrophic arthropods. Both, fertilization and embryonic development occur in the female gonad called ovariuterus. Two distinct reproductive patterns are recognized among scorpions: apoikogenic and katoikogenic. In the ovariuterus of apoikogenic scorpions growing oocytes protrude from the ovarian wall and continue previtellogenic and vitellogenic growth on the gonad surface being accompanied by the follicular cells that cover the oocyte surface, and, in most families, the stalk cells that join the oocyte with the ovariuterus wall. In the katoikogenic ovariuterus the oocytes grow in outpocketings of the ovarian wall called diverticula. The aim of our study was to show the development and structure of the diverticula in two katoikogenic scorpions from the family Scorpionidae: Ophistothalmus boehmei and Heterometrus spinifer. We show that the somatic components of each diverticulum develop from the two epithelial layers of the ovariuterine wall. Before fertilization, the wall of the mature diverticula consists of two distinctive epithelial layers: an internal and an external one. Our observations reveal that the epithelial cells of the internal layer of the diverticulum show striking morphological resemblance to the follicular and stalk cells that accompany the growing oocytes in some apoikogenic scorpions. The external epithelial layer of the katoikogenic diverticulum seems to have no equivalents in the apoikogenic type. Functions of the somatic cells of the diverticulum are discussed.