A comparison of embryonic development of two Onchidiid species

Abstract:

Onchidiidae is one of the higher clades of pulmonates. Most of them are marine organism and live in the intertidal zone, in rocky, sandy, or muddy habitats, including mangroves. In China, previous studies on Onchidiidae mainly focused on Onchidium struma. Platevindex mortoni and Paraoncidium reevesii are new record ones in mainland China. Their embryonic development process can be divided into seven stages: cleavage, blastula, gastrula, intracapsular trochophore, veliger in capsule and free-swimming veliger stage. The embryonic development of Platevindex mortoni and Paraoncidium reevesii were observed and described. The morphological characteristics of every period of larvae were recorded under microscopic observation, and the time series table of embryonic and larval development was confirmed and compared with Onchidium struma. Results showed: different Onchidiid species have significant differences in zygote biological parameters and the time required for fertilized eggs to hatch. At the average water temperature of 28℃ and salinity of 15, the time period from the fertilized eggs hatching to the free-swimming veliger stage required for three Onchidiid species was 210 h, 253 h and 270 h respectively. We did not observe the development of larvae for they all died in creeping larva stage. More work still needs to be done to ascertain the condition and process of metamorphosis for pelagic veliger.