MORPHOLOGICAL AND ORGAN CHANGES, MOVEMENT AND FEEDING OBSERVATION IN THE METAMORPHOSIS OF THE LARVAE OF PINCTADA FUCATA

To reveal the characteristics of external morphology and internal organ during the growth and development of larvae to juveniles of pearl oyster Pinctada fucata and the relationship between morphology, organs and motion, ingestion behavior, optical microscopy was used for observations and nonlinear regression parameters were used for descriptions. The results showed that during the normally larval rearing, the growth of shell length was accelerated positi-vely, the growth of shell height was decelerated positively, the growth of hinge length was accelerated negatively, the growth of shell height was faster than that of the shell length, and the growth of hinge length was slower than that of the shell length. When the larvae grown to a shell length of (209.26±9.22) μm, the internal organs began to change, the velum gradually degene-rated and developed into a gill, and the foot gradually formed. when the shell length reached (234.30±14.00) μm, the secondary shell appeared and the external morphology gradually changed to the juvenile. In the juvenile stage, the growth of gill filament length, gill filament distance and number of gill filament were slower than that of shell length. The larvae swim and filter microalgae by beating their cilia. When swimming, the double shells on the top of the larvae opened the umbo toward the bottom, and the velum projecting from back of the shell is used to propel the body. Larvae swim around clockwise with a certain radius in the vertical direction with a spiral either rising or falling. In the juvenile stage, the reciprocating expansion of the foot and the filtration of the sputum conducted the crawling and the feeding, respectively. During the metamorphosis of larvae stage, the velum is degraded, the motor function of the metamorphosis larvae is reduced, the feeding function has disappeared, larvae relied on reserved energy to complete growth and organ development, which is an important step in larval rearing.