Stage I (between 0 and 12 hours after laying)--Immediately after cocoon laying, 4 to 16 egg cells, within a large number of yolk cells, are observed.
All the yolk cells, which were placed around the embryo in the previous stage, are absorbed into the embryo.
(2006), the second type of yolk cells of Schmidtea polychroa (Schmidt, 1861), the so-called fusiform yolk cells, differentiates from spherical yolk cells.
tigrina), formation of a embryonic gut cavity which contains the yolk cells engulfed by the embryonic pharynx (stages III of P.
In most arthropod species, the yolk nuclei or yolk cells
function only as vitellophages, degenerating before the end of embryonic development (Anderson, 1973; Campos-Ortega and Hartenstein, 1997).
Table 1 Description of embryo stages of Callinectes sapidus Elapsed Time Stage Description (hours at 27[degrees]C) 1 Fertilization 0 2 Early cleavage; morula 12 (random mass of yolk cells
) 3 Late cleavage; blastula 36 (mass of undifferentiated yolk cells
) 4 Embryonic naupliar stage; 85 transparent embryo above the yolk 5 Early appendage fomation; 110 embryo invading ventral portion of yolk 6 Embryonic eye; eye appears 160 as scarlet crescent; elongating appendages 7 Presence of beating heart; 180 pigmented appendages 8 Oval, pigmented eye; 50% 210 of yolk utilized; clear appendages 9 Compound eye with dark 230 pigmentation; only small amounts of yolk 10 Protozoeae stage ready 280 for hatching into free-swimming zoea Acknowledgments