Observations on the embryonic and early post-embryonic development of Rossia macrosoma (Mollusca, Cephalopoda)

Abstract

1. Egg masses of Rossia macrosoma were collected by bottom trawling in the Western Mediterranean. The ultrastructure of the peculiar outer case of the egg is described. 2. The embryonic development was followed at a constant temperature (15° C); a graphic presentation of developmental rates throughout the embryogenesis is given. Problems concerning the length and the course of embryonic development are discussed. 3. Embryogenesis is briefly described and figured. A few remarks are made on the organogenesis of the arm-funnel complex, the alimentary canal, the shell sac and the vena cava. Emphasis is placed on the dynamics of embryogenesis. 4. The mechanism of yolk absorption during later embryonic development includes collecting and transfer (to the hepatopancreas) of nutritive material by means of the yolk "vessels" (former yolk sinus). 5. For hatching, the secretory action of the Hoyle organ is followed by breaking the outer egg case, which is possibly facilitated by the muscular mantle "spine". 6. Hatched animals were raised in the laboratory for several months, under varying conditions. The observations on growth and behaviour are discussed, earlier observations and field data being considered. © 1973 Biologischen Anstalt Helgoland.