Culture and development of the polychaete Perinereis cf. nuntia

The polychaete Perinereis cf. nuntia, a tropical species endemic in Thailand, was cultured in captivity as follows: eggs and sperm from sexually mature (epitokous) P. cf. nuntia, were artificially fertilized, and settled into a sand bed about 30 cm deep at the nectochaete stage. The sand beds were supplied with seawater at 30-ppt salinity and the nectochaetes reared for five months after which time some adults were becoming epitokes. The culture method yielded 3-4 kg polychaetes at an atokous stage per m2 of culture area. Because the polychaetes were to be used to feed shrimp broodstock, samples of the worms were screened for the presence of white-spot syndrome and yellow-head viruses using polymerase chain reaction (PCR) methods prior to introduction to the system as founders and at monthly intervals during their culture. Morphological details of P. cf. nuntia from fertilization to nectochaete stage are described using light microscopy, transmission (TEM) and scanning electron microscopy (SEM). The egg is surrounded by a chorion layer, TEM reveals that the microvillous tip vesicles are putative sites for the binding of the sperm to the egg surface. TEM studies of the cortical reaction show that the cortical alveoli contain a fibrous substance which, after fertilization and membrane fusion, passes into the perivitelline space to form part of the fertilization membrane, as well as being secreted from the egg surface to form a jelly layer surrounding the egg.