The nephridial hypothesis of the gill slit originстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 27 января 2016 г.
Аннотация:Dorsal wall of enteropneust pharynx is perforated by metameric gill slits, running to branchial sacs and connecting with the environment by gill pores. We describe the microscopic anatomy of the branchial apparatus, and the fine structure of gill skeleton elements and gill bars in Saccoglossus mereschkowskii. Form of all gill slits, except the first pair, is supported by trident skeletal elements descending within the gill bars. The gill bars are simple vertical folds of pharyngeal epithelium fused by their basal laminae. The overgrowths of fibrillar layer in these fusings form the gill skeletal elements. The first pair of gill skeletal elements has only two prongs. The first pair of pharyngeal slits is not gill itself, and does not connect with the environment; they open to the branchial sac of the second gill pair, and besides that, communicate with the collar coelom by a pair of collar coelomoducts. Thus, the first pair of gill slits has not only the branchial function, but represents the pair of enteronephridia. Such association of enteropneust coelomoducts and gill slits, and double function of the first gill slit allows us to suggest the hypothesis of gill slit origin from metameric excretory organs. Perhaps, in ancestral organisms, each metameric segment contained two independent organs: the
nephridial funnel and canal to the exterior, and the enteronephridium, without the connection with environment. After fusing of these both organs, each nephridium led both to the gut and to the exterior and formed the gill slit and gill pore.