Embryonic development of the solar-powered nudibranch Phyllodesmium lizardensis (Gastropoda: Nudibranchia)

In this pilot study we investigated the early embryonic development of the recently described solar-powered nudibranch species Phyllodesmium lizardensis. In previous studies P. lizardensis has been used as a model system to study the symbiosis between nudibranchs and their symbiotic dinoflagellates Symbiodinium, but the transmission mode of symbionts in the life cycle of this species remained unknown. Embryonic development in P. lizardensis was similar to related nudibranch taxa. Specimens laid clear gelatinous egg masses filled with relatively small egg capsules (81.25 +/- 3.78 mu m, n=11). Zygotes developed into planktotrophic veliger larvae that hatched after about 85 hours. No Symbiodinium cells could be detected by means of light microscopy at any developmental stage in zygotes or unhatched veliger larvae. Vertical transmission of symbionts is therefore unlikely; the timing of Symbiodinium acquisition by this species remains unknown.