First survey of heterobranch sea slugs (Mollusca, Gastropoda) from the island Sangihe, North Sulawesi, Indonesia

Indonesia is famous for its underwater biodiversity, which attracts many tourists, especially divers. This is also true for Sangihe Islands Regency, an area composed of several islands and located in the northern part of Sulawesi. However, Sangihe Islands is much less known than, e.g., the islands of Bunaken National Park (BNP), North Sulawesi, or Bali. The main and largest island, Sangihe, has come into focus lately, resulting in an increase in tourism and other activities with impacts on the environment. Recently, monitoring projects began around BNP using marine Heterobranchia as indicators for coral reef health. No information about this taxon exists from the more remote islands in the north of Sulawesi and it is the intention of the present study to start monitoring the marine Heterobranchia around the biggest island of Sangihe Islands Regency, namely Sangihe. In total, 250 specimens, which could be assigned to 23 species, were sampled around Sangihe by diving and snorkelling at seven sites. These species belong to Sacoglossa (3), Anthobranchia (19), and Cladobranchia (1). In comparison to BNP, the number of species is low, 23 versus 172 species. However, at least eight species (35 %) collected around Sangihe are not recorded from BNP, probably indicating differences in habitat. Here we also report for the first time a Chromodoris annae specimen mimicking C. elisabethina, and the discovery of a new Phyllidia species.