title: Comparison of hatching mode in pelagic and demersal eggs of two closely related species in the order pleuronectiformes.
abstract: We compared several characteristics of the pelagic eggs of Verasper variegatus with those of demersal eggs of Pseudopleuronectes yokohamae, both in the order Pleuronectiformes (halibuts or flatfishes). V. variegatus eggs had about twice the diameter of P. yokohamae eggs. However, the total egg protein weight of P. yokohamae was similar to that of V. variegatus. The specific gravity of P. yokohamae eggs was calculated to be 7-fold that of V. variegatus. The difference in size is the main feature distinguishing the two types of egg. The thickness of the egg envelope of P. yokohamae- more than twice that of V. variegatus-must affect the manner of hatching. The amount of hatching enzyme synthesized in pre-hatching embryo was estimated to be larger in P. yokohamae than V. variegatus. The distribution of hatching gland cells differed between the species. In V. variegates embryos, these were located on the yolk sac as a narrow ring-shaped belt, resulting in cleavage of the egg envelope into two parts by digesting a limited region of the egg envelope, called "rim-hatching". The hatching gland cells of P. yokohamae embryos were distributed all over the surface of the yolk sac, forming a hole through which the embryo could escape. Thus, the location of the hatching gland cells in pre-hatching embryos varied during the evolution of the Pleuronectiformes, depending on the egg type and manner of hatching.
authors.affiliation: 1 Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan.
authors.forename: Mari
authors.initials: M
authors.lastname: Kawaguchi
authors.forename: Kaori
authors.initials: K
authors.lastname: Sano
authors.forename: Norio
authors.initials: N
authors.lastname: Yoshizaki
authors.forename: Daisuke
authors.initials: D
authors.lastname: Shimizu
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Fujinami
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Noda
authors.forename: Shigeki
authors.initials: S
authors.lastname: Yasumasu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005412:Flatfishes / Q000145:classification* / Q000235:genetics / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic; D008666:Metalloendopeptidases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010063:Ovum / Q000145:classification* / Q000502:physiology* / Q000648:ultrastructure; D010802:Phylogeny; D013045:Species Specificity
chemical_list: D008666:Metalloendopeptidases; C024344:envelysin
keywords: astacin protease family; demersal egg; egg envelope; hatching enzyme; pelagic egg