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Investigations on the biochemical relationship between Doriprismatica stellata (Chromodorididae, Doridoidea) nudibranchs, their egg ribbons, and the associated dietary sponge Spongia cf. agaricina (Demospongiae, Porifera) led to the isolation of the structurally new scalarane-type sesterterpene 12-deacetoxy-4-demethyl-11,24-diacetoxy-3,4-methylenedeoxoscalarin, with an unprecedented position of the cyclopropane ring annelated to the ring A. Unlike other scalaranes, which are most often functionalized at C-12 of ring C, it bears two acetoxy groups at C-11 and C-24 instead. The compound was present in all three samples, supporting the dietary relationship between chromodorid nudibranchs of the genus Doriprismatica and scalarane-containing dictyoceratid sponges of the Spongiidae family. The results also indicate that D. stellata passes the scalarane metabolite on to its egg ribbons, most likely for protective purposes. The scalarane showed antibacterial activity against the Gram-positive bacteria Arthrobacter crystallopoietes (DSM 20117) and Bacillus megaterium (DSM 32).

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 in the northern part of North Sulawesi. However, Sangihe Islands Regency is much less known than, e.g., Bunaken National Park (BNP, North Sulawesi). The main island, Sangihe, has recently experienced an increase in tourism and mining activities with potentially high impact 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 remote islands in North Sulawesi. The present study represents the first monitoring study ever and focuses on marine Heterobranchia around Sangihe. In total, 250 specimens were collected, which could be assigned to Sacoglossa (3), Anthobranchia (19), and Cladobranchia (1). Despite the low number (23 versus 172 in BNP), at least eight species (35%) are not recorded from BNP, probably indicating differences in habitat, but also influence of a strong El Ni&ntilde, o year in 2016. Here we also report for the first time a Chromodoris annae specimen mimicking C. elisabethina, and the discovery of a new Phyllidia species.

We describe a new species, Moridilla jobeli sp. nov., belonging to the marine heterobranch group Aeolidioidea. Up to now, it is only recorded from Bunaken National Park, North Sulawesi, Indonesia. A combination of histological, computer tomographic and scanning electron microscopic methods was applied in order to describe and illustrate the anatomy of Moridilla jobeli sp. nov. in detail. Furthermore, we conducted molecular analyses which include available partial COI and 16S rRNA sequences, as well as the nuclear gene Histone 3 (H3) of Facelinidae and Aeolidiidae. NeighborNet analyses, species delimitation tests and phylogenetic reconstruction methods show the distinctiveness of the new species from the type species Moridilla brockii Bergh, 1888 and the two recently described species Moridilla fifo Carmona & Wilson, 2018 and Moridilla hermanita Carmona & Wilson, 2018, as well as the monophyly of the genus. A phylogenetic analysis of the Facelinidae and Aeolidiidae does not result in a resolved tree, therefore relationship of former assumed closely related genera, Noumeaella Risbec, 1937 and Palisa Edmunds, 1964, cannot be discussed in detail.

Bunaken National Park has been surveyed for a fourth time in 14 years, in an attempt to establish the species composition of heterobranch sea slugs in a baseline study for monitoring programs and protection of this special park. These molluscs are potentially good indicators of the health of an ecosystem, as many are species-specific predators on a huge variety of marine benthic and sessile invertebrates from almost every taxonomic group. Additionally, they are known to contain bio-compounds of significance in the pharmaceutical industry. It is therefore of paramount importance not only to document the species composition from a zoogeographic point of view, but to assist in their protection for the future, both in terms of economics and aesthetics. These four surveys have documented more than 200 species, with an approximate 50% of each collection found only on that survey and not re-collected. Many species new to science have also been documented, highlighting the lack of knowledge in this field.

Background Bunaken National Park (BNP) is one of the most famous marine national parks in Indonesia with an extraordinary diversity in marine life forms. However, this diversity is threatened by an increasing population on the islands, ongoing destructive fishing techniques and lately by an increase in tourism. Protecting and managing the future use of BNP resources will require the assessment of both, local marine biodiversity through monitoring efforts and the identification and subsequent reduction of any threats or changes in the park. A high diversity in marine Heterobranchia indicates a high diversity of metazoan life forms and a diverse habitat structure. Surveying the complete biological diversity across taxonomic groups found in BNP would be an extensive undertaking, so focus on heterobranch diversity as an indicator of coral reef health was initiated and a model group on which future monitoring and conservation efforts can be based is provided. This study follows up the first investigation of marine Heterobranchia in BNP, conducted 12 years ago, while assessing molluscan diversity, and intends to present a base line for future monitoring programs. Results The diversity of marine heterobranchs around BNP was surveyed with an emphasis on Bunaken Island by diving and snorkeling at nearly 20 sites. Species are listed with photographic documentation (81 species) and results compared with the former study on molluscan species diversity in BNP. Taking these two studies into account 135 species are now recorded from BNP. The low overlap of described species (21) between the two BNP studies illustrates the gap of knowledge about overall species diversity in this particular area. A comparison with other studies from the region and Indo-Pacific also provides evidence for undersampling, but show similar taxa composition except of a somewhat higher cladobranch number in relation to Anthobranchia. Conclusions BNP is still under-sampled with regard to sea slug diversity. Thus conclusions as to whether or not a shift in species has occurred during the 12 years since the first study cannot be drawn. More and extensive studies are necessary to completely document the species richness in this area.

The Splanchnotrophidae are a worldwide-distributed family of endoparasitic copepods, utilising shell-less opisthobranch gastropod hosts. Using scanning electron microscopy, we describe three new Ismaila Bergh, 1867 species infesting nudibranch hosts from southern Chile. Ismaila volatilis spec. nov. infests the proctonotid Janolus sp. and differs from all congeners by the size and number of dorsal bulges, the number of processes on the maxilla, and the thickness of thoracic appendages. Ismaila chaihuiensis spec. nov. was found in the doridoidean Diaulula punctuolata (D’Orbigny, 1837) and is diagnosed by a pore situated on a prominent bulge above the labrum. Ismaila genalis spec. nov. from a polycerid Holoplocamus papposus Odhner, 1926 host differs from its congeners in the size and form of the ventral bulges present on the head. These discoveries further broaden the range of splanchnotrophid host taxa; they are in line with earlier hypotheses of strict host specificity of Ismaila species and support Chile as a hotspot for Ismaila radiation. Herein, we present a key to the identification of all 14 Ismaila species. In Sulawesi (tropical Indo-West Pacific), Arthurius gibbosa spec. nov. infests the sacoglossan Elysia macnaei Marcus, 1982. The new species differs from both congeners by the short and stubby dorsal bulges. Uniquely among splanchnotrophids, long thoracic appendages are absent. Arthurius Huys, 2001 thus is the morphologically most divergent genus of the Splanchnotrophidae, but it is well characterized by the loss of several mouthparts and the preference for sacoglossan hosts. Currently, the distribution of the genus is limited to the Indo-West Pacific.

Nudibranchia, marine soft-bodied organisms, developed, due to the absence of a protective shell, different strategies to protect themselves against putative predators and fouling organisms. One strategy is to use chemical weapons to distract predators, as well as pathogenic microorganisms. Hence, these gastropods take advantage of the incorporation of chemical molecules. Thereby the original source of these natural products varies; it might be the food source, de novo synthesis from the sea slug, or biosynthesis by associated bacteria. These bioactive molecules applied by the slugs can become important drug leads for future medicinal drugs. To test the potential of the associated bacteria, the latter were isolated from their hosts, brought into culture and extracts were prepared and tested for antimicrobial activities. From 49 isolated bacterial strains 35 showed antibiotic activity. The most promising extracts were chosen for further testing against relevant pathogens. In that way three strains showing activity against methicillin resistant Staphylococcus aureus (MRSA) and one strain with activity against enterohemorrhagic Escherichia coli (EHEC), respectively, were identified. The obtained results indicate that the sea slug associated microbiome is a promising source for bacterial strains, which hold the potential for the biotechnological production of antibiotics.

Species trees were produced for the Indo-West Pacific (IWP) gastropod genus Lunella using MrBayes, BEAST, and *BEAST with sequence data from four genes. Three fossil records were used to calibrate a molecular clock. Eight cryptic species were recognized using statistical methods for species delimitation in combination with morphological differences. However, our results suggest caution in interpreting ESUs defined solely by the general mixed Yule Coalescent model in genera like Lunella, with lower dispersal abilities. Four almost entirely allopatric species groups were recovered that differ in ecology and distribution. Three groups occur predominantly along continental coastlines and one occurs on island arrays. Sympatric species occur only in the torquata and coronata groups along coastlines, whereas species in the cinerea group, distributed in two-dimensional island arrays, occur in complete allopatry. Dispersal along island arcs has been important in the maintenance of species distributions and gene flow among populations in the cinerea group. The emergence of new islands and their eventual subsidence over geological time has had important consequences for the isolation of populations and the eventual rise of new species in Lunella.

Aim This study aimed to test monophyly and geographical boundaries in five marine intertidal snail species from the central Indo-West Pacific. We tested the prediction that phylogenetic breaks between the Indian and Pacific Ocean basins should be more pronounced in continental than oceanic settings, and sought common geographical patterns of interspecific boundaries and intraspecific phylogenetic breaks in the region. Location The tropical seas of the Indo-West Pacific. Methods We sequenced over 1200 bp of the mitochondrial cytochrome oxidase subunit I gene (COI) from 18–92 individuals sampled from throughout the ranges of each of five species of Echinolittorina (Littorinidae): three members of the Echinolittorina trochoides species complex; Echinolittorina reticulata; and Echinolittorina vidua, together with sister species, in order to test species boundaries. In addition, 630 bp of the nuclear 28S rRNA gene were sequenced from E. reticulata and its sister Echinolittorina millegrana. Phylogenetic structure was assessed using neighbour-joining and parsimony analyses. Results COI data confirmed species boundaries and geographical distributions for all species except the pair E. reticulata and E. millegrana, which were nevertheless reciprocally monophyletic for 28S rRNA. The species from ecologically ‘continental’ habitats (E. trochoides A and E. vidua, but not E. trochoides B) mostly showed strong interoceanic breaks (with age estimates 0.58–4.4 Ma), while the ecologically ‘oceanic’E. trochoides D and E. reticulata did not. The sister species E. trochoides A and B occupy the shores of the continental shelves of Southeast Asia and Australasia respectively; between them lies the oceanic ‘eastern Indonesian corridor’ occupied by E. trochoides D and E. reticulata. The widespread continental species E. vidua showed a complex pattern of deep division into six haplotype clades with apparently parapatric distributions. Main conclusions Our results show that ecological differences (in this case continental vs. oceanic habitat) influence both intraspecific phylogenetic structure and interspecific boundaries in these snails of intertidal rocky shores. Two of the three species restricted to continental shelves show phylogenetic breaks between the Indian and Pacific Oceans, consistent with vicariant separation during Plio-Pleistocene low sea levels. The two oceanic species do not show breaks, suggesting that they maintained interoceanic connections through the eastern Indonesian corridor. The geographical location of the interspecific boundary between continental E. trochoides A and oceanic E. trochoides D mirrors intraspecific breaks reported in other species. The sister relationship of E. trochoides A and B in Asia and Australasia, respectively, is an example of a ‘marine Wallace's line’ distribution, and we suggest that it is the result of separation of two continental species by a barrier of unsuitable oceanic habitat.