Embryonic and larval development of Pteria penguin (Roding, 1798) (Bivalvia: Pteriidae)

This study describes the processes of embryogenesis, shell formation and larval development of the winged pearl oyster, Pteria penguin. Broodstock were induced to spawn using the standard method of thermal stimulation and fertilized eggs were incubated at a density of 50 ml−1 and a temperature of 27 ± 1°C. After an incubation period of 24 h, shelled larvae were stocked at 3 ml−1 and fed a mixed microalgae diet until reaching settlement age. Embryos and larvae were sampled periodically for examination by scanning electron microscope. The resulting high-resolution images were used to record the timing of developmental stages including the first cleavage (1 h postfertilization, hpf), morula (2.5 hpf), blastula (4.5 hpf), gastrula (5.5 > hpf), trochophore (7 > hpf), D-stage (20–22 hpf), prodissoconch II (3–6 days posthatching, dph), umbone (10–12 dph) and pediveliger (22 dph). Comparison with other oviparous oyster species revealed a similar sequence of key events, with differences occurring in the timing of developmental stages, shell structure and shell shape. This study is the first to describe early shell formation for a species belonging to the family Pteriidae. Shell development begins with formation a shell-field invagination (sfi) at the dorsoposterior end of the embryo (7 hpf), indicating the creation of a shell gland. The sfi stretches laterally to create a deep crevice (9 hpf) before eventually everting to form a flat central hinge linking the two expanding shell valves (12 hpf).