Embryonic Nutrition and Yolk Utilization in the Sand Crab Emerita asiatica

This paper reviews information available on the composition of yolk and the pattern of yolk utilization during embryogenesis in an intertidal crab, Emerita asiatica, from the east coast of India. Emerita yolk primarily exists as a glycolipoprotein complex, conjugated with carotenoid pigment. In addition, free lipid globules and glycogen droplets are also stored in the ooplasm. Another feature of interest is the conjugation of several steroidal hormones such as ecdysteroids, estrogen and progesterone with the yolk molecules. The stage-specific release of a host of hydrolytic enzymes splits up the complex yolk molecules which not only serve as raw organic substrates for tissue build up, but also function as regulatory factors during embryogenesis. For example, the regulated release of active ecdysteroids from the conjugates at specific time during embryogenesis not only triggers embryonic cuticle formation but also accomplishes larval molting and egg hatching. In conclusion, the study on the Emerita yolk utilization provides information on energy release for embryogenesis as well as abbreviated larval development that occurs within the brooding egg in Crustacea.