Nudibranchia is the largest order of Opistobranchia which is known to have about 3,000 species.
Nudibranchia is a popular macro photography object among divers. Although Tulamben Waters, Bali is one of
popular destination for macrobiota’s habitat, but research on marine biota, especially nudibranchia in these
waters is still very rare. This study uses two methods, which is direct observation to reveal diversity and species
number, belt transect methods to estimate density or abundance per sampling area using diving techniques . A
transect line of 50 m at each point of observation site was used to evaluate abundance. This study wants to see
the level of diversity, mapping various species and abundance of nudibranchia. For biodiversity, 31 species from
15 families are found, Chromodoridae, Dorididae, Elysiidae, Facelinidae, Flabellinidae, Goniodorididae,
Halgerdidae, Hexabranchidae, Phyllidiidae Polyceridae, Hydatinidae, Costasiellidae, Elysiidae and Limapontiidae.
Whereas the transect method found 12 species from 6 families, Chromodoridae, Facelinidae, Phyllidiidae
Aglajidae, Costasiellidae, and Elysiidae. With a diversity index of 2.27 and the highest level of abundance found
in Pteraeolidia ianthina species with a relative abundance of 0.19%.