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Completely direct development of Abatus cordatus, a brooding schizasterid (Echinodermata: Echinoidea) from Kerguelen, with description of perigastrulation, a hypothetical new mode of gastrulation
Schatt, P.; Féral, J.-P. (1996). Completely direct development of Abatus cordatus, a brooding schizasterid (Echinodermata: Echinoidea) from Kerguelen, with description of perigastrulation, a hypothetical new mode of gastrulation. Biol. Bull. 190(1): 24-44. https://dx.doi.org/10.2307/1542673
In: The Biological Bulletin. Marine Biological Laboratory: Lancaster. ISSN 0006-3185; e-ISSN 1939-8697
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| Abstract |
Development of the brooding schizasterid Abatus cordatus, a subantarctic echinoid endemic to Ker-guelen, is described. Females spawn non-buoyant eggs 1300 pm in diameter, which are fertilized by elongated sperm (head 1 pm wide and 15 pm long). The main characteristics of this development are (1) incomplete cleavage beginning at the animal pole that becomes holoblastic, giving a filled wrinkled blastula 26 days after fertilization; (2) apparent (fate-mapping studies have not been done) external migration of mesenchyme cells, in the perivitelline space, from the animal to the vegetal pole during gastrulation while the archenteron invaginates; (3) hatching occurring at the end of the gastrulation (65 days after fertilization); (4) differentiation of the vestibule from a thickening of the oral epidermis as soon as the end of gastrulation is attained; and (5) production of a juvenile directly from the gastrula without any larval stage. The juvenile that leaves the brood chamber is 2 mm in diameter and about 250 days old. A. cordatus is a true completely direct developer (no larva and no metamorphosis). We propose to use (1) the term perigastrulation, as a tentative one until more definitive studies are available, to describe the hypothetical peculiar movement of cells during gastrulation and (2) the terms of direct development only for completely direct developing species and abbreviated development for species that have more or less transformed plutei. |
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