Researchers at University of Tsukuba have raised the nudibranch Hypselodoris festiva from eggs to adults in the laboratory and successfully observed larval settlement, metamorphosis, and the growth of juveniles. The growth process after settlement was classified into nine stages based on the changes in external morphology. To the best of our knowledge, this is the first report on the rearing of a sea slug belonging to the family Chromodorididae from eggs to adults in the laboratory.

Tsukuba, Japan—Nudibranchs are members of the phylum Mollusca, and most species have a planktonic larval stage characterized by the presence of shells immediately after hatching. During development, larvae settle on the seabed and reefs where they metamorphose, lose their shells, and shift from a floating to a benthic lifestyle. However, the species of the family Chromodorididae, including brightly colored sea slugs such as Hypselodoris festiva and Chromodoris orientalis, have never been raised from eggs to adults in the laboratory, and the growth process from settlement to adulthood has been shrouded in mystery.

Herein, the adults of H. festiva were collected and reared in the laboratory. They laid eggs, and approximately 6 days later, more than several thousands of floating larvae hatched from a single egg mass. Upon feeding with microalgae, eye spots and other features were formed and the larvae underwent metamorphosis about 3 weeks after hatching. During metamorphosis, they shed their shells and transitioned to a benthic lifestyle. The juveniles grew by feeding on sponges, which were also the food of adult H. festiva. During this process, the juveniles developed a bright blue and yellow pattern on their body and the main organs characterizing the adult stage, such as rhinophores, gills, and anus, were formed.

Based on the observed body color formation and organogenesis, the postsettlement growth of H. festiva was classified into nine stages: two metamorphic stages and seven juvenile stages. This classification allows the identification of the growth stages based on the external characteristics, with this study serving as a reference for further developmental studies of Chromodorididae. The appropriate rearing conditions for the larvae, juveniles, and adults of species belonging to Chromodorididae were previously unknown; however, the methods established in this study can be applied to not only H. festiva, but other species, and can contribute to industrial and commercial uses, such as aquarium displays.

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This work was partially funded by the JSPS KAKENHI (Grant No: 19H03279 and 24K02082) to HN and JST SPRING (Grant No: JPMJSP2124) to MH.

Original Paper

Title of original paper:

Staging of post-settlement growth in the nudibranch Hypselodoris festiva

Journal:

Scientific Reports

DOI:

10.1038/s41598-024-66322-4

Correspondence

Associate Professor NAKANO Hiroaki
Institute of Life and Environmental Sciences, University of Tsukuba

HAYASHI Makiko
Doctoral Programs in Biology, Degree Programs in Life and Earth Sciences, Graduate School of Science and Technology, University of Tsukuba

Related Link

Institute of Life and Environmental Sciences