Ovulation in Diplosoma (Tunicata, Ascidiacea, Didemnidae): a light microscopical study

Abstract

Serial sections of non-ovulated and ovulated eggs of Diplosoma migrans (Tunicata, Ascidiacea, Didemnidae) were compared in order to study the process of ovulation on the level of light microscopy. Fully grown eggs are surrounded by an outer follicular epithelium consisting of cubic cells, and an inner follicular epithelium consisting of flat cells. Egg release is initiated by a fusion of the epidermis with the outer follicular epithelium at the distal pole of the egg. A contraction of the outer follicular epithelium leads to an opening of both epidermis and outer follicular epithelium, and their removal from the egg. The envelope of ovulated eggs corresponds to the former inner follicular epithelium. Mainly due to a contraction of the epidermis, the outer follicular epithelium is shifted into the abdomen and separates from the epidermis. It transforms into a vestigial body (corpus luteum) and finally atrophies. The epidermis flattens and resumes its typical appearance. On the basis of these observations, the results of studies on the closely related Diplosoma listerianum are discussed and questioned.

Ascidian photosymbiosis: Diversity of cyanobacterial transmission during embryogenesis

“…In both modes, the host progenies acquire Prochloron cells in the cloacal cavity at a late stage in embryonic development. In didemnid ascidians, fertilization occurs in the ovary of each zooid (Burighel and Martinucci, ), after which early embryos are released into the tunic, where they develop into tadpole larvae (Groepler, ; Martinucci et al ., ). Because of this, the gametes and embryos have no contact with Prochloron cells until they enter the cloacal cavity in which the photosymbionts are located (Fig.…”

Bacterial community in the tunic matrix of a colonial ascidian Diplosoma migrans

“…The tunic of D. migrans usually harbors large numbers of different cell types (Groepler 1994). These cells make a thorough microbiological investigation inside the tunic difficult.…”

“…1). The tunic tissue is composed of different cells, including conspicuous bladder cells which are embedded in a structureless matrix (Groepler 1994). Fertilized eggs are released from ovarium to tunic, the embryonic development proceeds inside an envelope (Groepler 2002).…”