Morphology, Feeding Rate and Larval Settlement Preference of the Corallivorous Nudibranch Phestilla subodiosa (Nudibranchia: Trinchesiidae) from Hong Kong.

We studied the morphology, host specificity, feeding rate and larval settlement preference of the corallivorous nudibranch Phestilla subodiosa collected from the field. These specimens collected from the scleractinian coral Monipora peltiformis in Hong Kong waters are morphologically different from the holotype and paratypes collected from an aquarium culture of Montipora spp., as they have diamond-shaped swollen bulbs, and brown spots on cerata, as well as bulbs and the body immediately posterior to cerata. In experiments where P. subodiosa individuals were placed on the surface of several species of common scleractinian corals collected from Hong Kong waters, the nudibranchs were found to feed on M. peltformis at a rate of 0.05 cm2 individual-1 d-1; however, they were killed and eaten by other tested coral species (Pavnoa decussata, Porites lutea and Duncanopsammia peltata). When cultured in seawater conditioned with M. peltiformis, the veliger larvae required six days to become competent for settlement, and at day 9 could reach a maximum metamorphic rate of 31.1%. At competence, the veliger larvae could be induced to settle, indicating the presence of a larval settlement cue released by the host coral. Other coral species or their conditioned seawater did not induce settlement of the P. subodiosa larvae. Overall, our study expands the distribution record of P. subodiosa, adds this species to the list of corallivorous nudibranchs in Hong Kong waters, provides morphological features that were not included in the original description of this species, reveals the host specificity, and provides the feeding rate of this species. These results contribute to a better understanding of the diversity and potential impact of corallivorous nudibranchs in coral ecosystems.