The yolk syncytial layer (YSL) of Teleostei is a dynamic multifunctional temporary system. This paper describes the YSL structure of Misgurnus fossilis (Cobitidae) during its early developmental stages, studied using histological methods. YSL formation is prolonged. From the late blastula stage, the basal surface of the YSL is uneven and has protuberances, but becomes smoother during development. There are syncytial ‘islands’ with 1–2 yolk syncytial nuclei in the yolk mass. During epiboly, gastrulation and early segmentation, loach YSL is of different thickness in different regions along the dorso-ventral and antero-posterior axes of an embryo. The YSL is thickened in the dorsal region of gastrulae compared with the ventral region. Although the development of M. fossilis is similar to the development of zebrafish, there are important differences in YSL formation and organization that await further study and analysis. The study of YSL organization contributes to our knowledge of teleost developmental diversity and to the biology of temporary structures.

Cultivation of the geoduck Panopea zelandica (Quoy & Gaimard, 1835) requires knowledge on embryonic development to produce spat in hatcheries. This study investigated the development of P. zelandica embryos at 15°C and 35 ppt and the optimal sperm:egg ratios for fertilization under hatchery conditions. Panopea zelandica broodstock were induced to spawn by serotonin injection. Sperm and eggs were collected and fertilization was conducted at sperm:egg ratios of: 50:1, 100:1, 500:1, 1000:1 and 10,000:1 over 40 min. The optimal sperm:egg ratio was <500:1 and the normal embryo yield at 3 and 18 h post-fertilization (hpf) ranged from 83–96%. Panopea zelandica eggs (~80 μm diameter) developed the first and second polar bodies within 15–20 and 50–55 min post-fertilization, respectively. The blastula appeared at ~8 hpf, including the XR and XL cells and the presumptive shell field depression. Gastrulation occurred at 12–18 hpf with organic material apparent at the shell field depression. The mid-stage trochophore, which appeared at around 35 hpf had an apical plate with an apical tuft. The shell field spread to form the periostracum, which expanded and folded into right and left segments covering the late trochophore. The early D-stage veliger appeared at 45 hpf with the soft body being enclosed by two valves and the appearance of the velum. These observations will serve as the basis for future analyses of P. zelandica embryogenesis and for optimization of commercial production of D-veliger larvae.