The spawn and embryonic development of <i>Dendrodoris arborescens</i> (Collingwood, 1881) (Mollusca: Nudibranchia)

Dendrodoris arborescens is an ecologically important but poorly studied planktotrophic nudibranch species. By integrating artificial spawning, histology (Masson staining), light microscopy, and scanning-electron microscopy, the first systematic account of its reproductive biology and embryogenesis is provided in northern China. Adults are simultaneous hermaphrodites; reciprocal copulation results in paired, orange-yellow mucous egg ribbons. Within 9–10 days at 22–23 °C, embryos progress through cleavage, blastula, gastrula, intracapsular veliger, and planktonic veliger stages. Collagen-rich facial-disc larvae hatch with discernible rhinophore rudiments. SEM revealed distinct lipid droplet patterns in oocytes and a previously unreported incidence of polyspermy, as well as the birth of identical triplet larvae—both phenomena novel for Nudibranchia. These findings elucidate fundamental reproductive traits of planktotrophic nudibranchs and establish D. arborescens as a model for evolutionary-developmental studies of marine gastropods.