Effect of low-frequency noise on the survival rate and immunity of infected Vibrio parahaemolyticus sea slug (Onchidium reevesii).

Anthropogenic noise in the marine environment has become a global environmental pollutant that affects the behavior, physiology and immunity of marine animals. However, the resistance of marine animals to pathogens while under the influence of noise is a topic that has received little attention. To assess the immune defense response of sea slugs against pathogens when exposed to low frequency noise, we performed 120 h exposure experiments on sea slugs after a Vibrio parahaemolyticus application in low frequency noise at 500 Hz and 1000 Hz. We found that after the infection with V. parahaemolyticus, the survival rate of the sea slugs decreased, the apoptosis rate and reactive oxygen species (ROS) production of hemocytes increased significantly (P < 0.05), the proliferation of hemocytes accelerated, the activities of enzymes such as superoxide dismutase (SOD), catalase (CAT), alkaline phosphatase (AKP), alanine transaminase (ALT) and lysozyme (LZM) in the hepatopancreas increased significantly, and the expression of TNF signaling pathway-related genes (TNF-α, FADD, Caspase 8, Caspase 3) and Hsp70 genes were generally upregulated. In addition, exposure of sea slug after infected with V. parahaemolyticus to low frequency noise resulted in a significant increase in both antioxidant and immune parameters, which were positively correlated with frequency. The results showed that noise frequency and exposure time had an interactive effect on the above indicators. In summary, low-frequency noise exposure increases the risk of pathogenic infections in sea slugs and exacerbates the negative effects on the antioxidant capacity and immune metabolism of the organism.

Ceratosomicola oki n. sp., a New Species of Copepod (Cyclopoida: Splanchnotrophidae) Parasitic on the Chromodoridid Nudibranch Glossodoris misakinosibogae Baba, 1988 Off the Oki Islands, Japan, with Microanatomical Observation Using Micro-CT.

A new species of the family Splanchnotrophidae Norman and Scott, 1906 (Cyclopoida) is described based on both sexes collected from off the Oki Islands, the Sea of Japan. Specimens of both sexes of Ceratosomicola oki n. sp. were found in the body cavities of Glossodoris misakinosibogae Baba, 1988 (Nudibranchia: Chromodorididae). The copepod is characterized by the following female characters: the cephalosome with a pair of dorsolateral horn-like processes; the prosome with hemispherical posterolateral lobes on the middle region. Non-destructive, micro-computed tomography (micro-CT) imaging performed on a single specimen of the nudibranch revealed a heavy infection by a total 17 specimens of C. oki n. sp. Almost all individuals of the copepod were attached on the surface of the middle to posterior parts of the visceral sac, forming a dense cluster. The four females bearing developed lateral processes on the prosome faced the anterior end of the visceral sac and positioned the posterior tip of the body under the secondary gills of the host. The males fitted in the gaps between the females' bodies. Further, the distribution and shape of the reproductive organs of both sexes were partially clarified by micro-CT imaging.

Most Cephalaspidea have a shell, but transcriptomes can provide them with a backbone (Gastropoda: Heterobranchia).

Cephalaspidea is an order of marine gastropods found worldwide, often in sandy or muddy habitats, which has a convoluted taxonomic history based on convergent or ill-defined morphological characters. The cephalaspidean shell-which can be external and robust, internal, or altogether absent in the adult-is of particular interest in this group, and a well-resolved phylogeny can give us greater insight into the evolution of this character. Molecular data have clarified many relationships within Cephalaspidea, but studies involving few Sanger sequenced phylogenetic markers remain limited in the resolution they provide. Here we take a phylogenomic approach, the first to address internal cephalaspidean relationships, sequencing and assembling transcriptomes de novo from 22 ingroup taxa-representing the five currently accepted superfamilies, 10 of the 21 currently recognized families, and 21 genera-and analyzing these along with publicly available data. We generated two main datasets varying by a minimum taxon occupancy threshold (50% and 75%), and analyzed these using maximum likelihood, Bayesian inference and a coalescence-based method. We find a consistent, well-supported topology, with full support across most nodes including at the family and genus level, which also appears to be robust to the effect of compositional heterogeneity among amino acids in the dataset. Our analyses find Newnesioidea as the sister group to the rest of Cephalaspidea. Within the rest of the order, Philinoidea is the sister group to a clade that comprises (Bulloidea (Haminoeoidea, Cylichnoidea)). There is strong support for several previously suggested, but tenuously supported relationships such as the genus Odontoglaja nesting within the family Aglajidae, and a sister group relationship between Gastropteridae and Colpodaspididae, with Philinoglossidae as their sister group. We discuss these results and their implications in the context of current cephalaspidean taxonomy and evolution. Genomic-scale data give a backbone to this group of snails and slugs, and hold promise for a completely resolved Cephalaspidea.

Development of Cerata in the Cladobranchian Sea Slug Pteraeolidia semperi (Mollusca: Gastropoda: Nudibranchia).

Cladobranchian sea slugs are characterized by a number of dorsal projections, called "cerata," which are presumably involved in such biological functions as kleptocnidal defense, gas exchange, and symbiotic photosynthesis. Here, we investigated the developmental pattern of ceras formation in a cladobranchian, Pteraeolidia semperi, using field-collected individuals at various postembryonic developmental stages. As the body length increased, the total number of cerata increased in a logistic manner, up to 280 per individual. On the dorsal side of the body, the cerata exhibited a conspicuous formation of repeated, laterally-paired clusters, or rows, along the antero-posterior axis of the animals. As the body length increased, the number of ceras rows increased in a logistic manner, reaching a plateau at around 15 rows per individual. Two types of ceras clusters were observed: well-developed ceras clusters forming a glove-like structure with a basal bulge, which tended to be found in larger animals and at the anterior body region, and less-developed ceras clusters without the bulge, which tended to be found in smaller animals and at the posterior body region. Statistical and simulation analyses suggested that bulge formation underlies increased ceras number, even after the plateaued formation of new ceras rows. These results indicate that, in the postembryonic development of P. semperi, the increase of dorsal cerata entails the following processes: (i) increase of the number of ceras rows, (ii) formation of the basal bulge in each ceras cluster, and (iii) increase of the number of cerata per ceras cluster.

The Potential of Indonesian Heterobranchs Found around Bunaken Island for the Production of Bioactive Compounds.

The species diversity of marine heterobranch sea slugs found on field trips around Bunaken Island (North Sulawesi, Indonesia) and adjacent islands of the Bunaken National Marine Park forms the basis of this review. In a survey performed in 2015, 80 species from 23 families were collected, including 17 new species. Only three of these have been investigated previously in studies from Indonesia. Combining species diversity with a former study from 2003 reveals in total 140 species from this locality. The diversity of bioactive compounds known and yet to be discovered from these organisms is summarized and related to the producer if known or suspected (might it be down the food chain, de novo synthesised from the slug or an associated bacterium). Additionally, the collection of microorganisms for the discovery of natural products of pharmacological interest from this hotspot of biodiversity that is presented here contains more than 50 species that have never been investigated before in regard to bioactive secondary metabolites. This highlights the great potential of the sea slugs and the associated microorganisms for the discovery of natural products of pharmacological interest from this hotspot of biodiversity.

Family matters: The first molecular phylogeny of the Onchidorididae Gray, 1827 (Mollusca, Gastropoda, Nudibranchia).

Recent investigations into the evolution of the Onchidorididae using morphological based methods have resulted in low support for relationships among genera. This study aims to determine if molecular data corroborates recent morphological interpretations of the evolution of Onchidorididae. Five genetic markers: 16S, 18S, 28S, cytochrome c oxidase 1 (COI) and histone 3 (H3), were sequenced from 32 species comprising Onchidorididae and five other families, three from Phanerobranchia and two from Cryptobranchia. Phylogenies were estimated using maximum likelihood, and Bayesian inference analyses; with both yielding similar topologies. Molecular analyses resulted in high support for the monophyly of the suctorian clade and the placement of the genera within Onchidorididae. However, the Onchidorididae forms a paraphyletic grouping due to the recovery of the Goniodorididae and the Akiodorididae nested within family. In addition, the placement of Corambe as the most derived member of Onchidorididae is contradicted by the present study. Rather it is sister to a large clade that includes Acanthodoris and the species traditionally placed in Onchidoris and Adalaria, now defined as Onchidorididae. We have chosen to maintain Corambidae as a distinct taxon (including Corambe and Loy), sister to Onchidorididae. We also maintain Goniodorididae, Akiodorididae and Calycidoridae (including Calycidoris and Diaphorodoris), which along with the Onchidorididae and Corambidae comprise the suctorian superfamily Onchidoridoidea. Ancestral character reconstruction also suggests that the formation of a gill pocket, a character that currently defines the Cryptobranchia, may have evolved multiple times from an ancestor that lacked the ability to retract its gills into a fully formed gill pocket. The diversity of gill morphology displayed by the Onchidoridoidea will help give new insight into the evolution of this complex character within the Nudibranchia.

Division of labor for defensive retaliation and preemption by the peripheral and central nervous systems in the nudibranch Berghia.

Relatively little is known about how peripheral nervous systems (PNSs) contribute to the patterning of behavior in which their role transcends the simple execution of central motor commands or mediation of reflexes. We sought to draw inferences to this end in the aeolid nudibranch Berghia stephanieae, which generates a rapid, dramatic defense behavior, "bristling." This behavior involves the coordinated movement of cerata, dozens of venomous appendages emerging from the animal's mantle. Our investigations revealed that bristling constitutes a stereotyped but non-reflexive two-stage behavior: an initial adduction of proximate cerata to sting the offending stimulus (stage 1) followed by a coordinated radial extension of remaining cerata to create a pincushion-like defensive screen around the animal (stage 2). In decerebrated specimens, stage 1 bristling was preserved, while stage 2 bristling was replaced by slower, uncoordinated ceratal movements. We conclude from these observations that, first, the animal's PNS and central nervous system (CNS) mediate stages 1 and 2 of bristling, respectively; second, the behavior propagates through the body utilizing both peripheral- and central-origin nerve networks that support different signaling kinetics; and third, the former network inhibits the latter in the body region being stimulated. These findings extend our understanding of the PNS' computational capacity and provide insight into a neuroethological scheme in which the CNS and PNS both independently and interactively pattern different aspects of non-reflexive behavior.

Assessing the Trophic Impact of Bleaching: The Model Pair Berghia stephanieae/Exaiptasia diaphana.

Bleaching events associated with climate change are increasing worldwide, being a major threat to tropical coral reefs. Nonetheless, the indirect impacts promoted by the bleaching of organisms hosting photosynthetic endosymbionts, such as those impacting trophic interactions, have received considerably less attention by the scientific community. Bleaching significantly affects the nutritional quality of bleached organisms. The consequences promoted by such shifts remain largely overlooked, namely on specialized predators that have evolved to prey upon organisms hosting photosynthetic endosymbionts and benefit nutritionally, either directly or indirectly, from the available pool of photosynthates. In the present study, we advocate the use of the model predator-prey pair featuring the stenophagous nudibranch sea slug Berghia stephanieae that preys upon the photosymbiotic glass anemone Exaiptasia diaphana to study the impacts of bleaching on trophic interactions. These model organisms are already used in other research fields, and one may benefit from knowledge available on their physiology, omics, and culture protocols under controlled laboratory conditions. Moreover, B. stephanieae can thrive on either photosymbiotic or aposymbiotic (bleached) glass anemones, which can be easily maintained over long periods in the laboratory (unlike photosymbiotic corals). As such, one can investigate if and how nutritional shifts induced by bleaching impact highly specialized predators (stenophagous species), as well as if and how such effects cascade over consecutive generations. Overall, by using this model predator-prey pair one can start to truly unravel the trophic effects of bleaching events impacting coral reef communities, as well as their prevalence over time.

The complete mitochondrial genome of Spurilla braziliana MacFarland 1909 (Nudibranchia, Aeolidiidae).

Spurilla braziliana MacFarland 1909 is a morphologically diverse nudibranch found in the Pacific and Western Atlantic. The complete mitochondrial genome of S. braziliana has been constructed using next-generation sequencing technology. The mitochondrial genome is 14,291 bp and contains 13 protein-coding genes, 2 rRNA genes, and 23 tRNA genes. Molecular phylogenetic analysis using the maximum likelihood method revealed that S. braziliana is included in the superfamily Aeolidioidea and forms a monophyletic group with Berghia stephanieae, a nudibranch of the family Aeolidiidae. This study reinforces existing taxonomic insights and provides a basis for further molecular phylogenetic analysis.

Peruvian nudibranchs (Mollusca, Gastropoda, Heterobranchia): an updated literature review-based list of species.

Nudibranchs, as a group, have received limited attention in terms of scientific study along the coastline of Peru. Here, an updated and comprehensive list of nudibranch species found in the Peruvian sea is presented, compiled through an extensive review of relevant literature. This compilation encompasses a total of 31 species, classified into two suborders, 10 superfamilies, 20 families, and 28 genera. With respect to the biogeographic provinces along the Peruvian coast, 23 species inhabit the Warm Temperate Southeastern Pacific province, 18 species occur in the Tropical Eastern Pacific province, and 10 species are found in both provinces, crossing the transitional zone between them. In terms of distribution patterns, two species exhibit a cosmopolitan distribution (Glaucusatlanticus and Fionapinnata), while two species display a circumtropical distribution (Cephalopygetrematoides and Phylliroebucephala). One species exhibits a bipolar distribution in the Eastern Pacific and possesses an amphi-South American distribution (Rostangapulchra). Additionally, six species exhibit an amphi-South American distribution (Rostangapulchra, Diaululapunctuolata, Dotouva, Tyrinnaevelinae, Tyrinnadelicata, and Dorisfontainii), and two species are endemic to Peru (Corambemancorensis and Felimaresechurana). This study provides comprehensive information on biogeographical aspects, geographical distributions, and taxonomic updates within the nudibranch species documented in Peru. Furthermore, we discuss the status of species listed in previous literature that have not been confirmed by collections, referring to them as potentially occurring species.

The complete mitochondrial genome of sea slug phyllidia elegans bergh, 1869 (nudibranchia, phyllidiidae) from the South China sea.

In this study, the complete mitochondrial genome (mitogenome) sequence of sea slug, Phyllidia elegans Bergh, 1869 (Nudibranchia, Phyllidiidae), was sequenced and characterized. The assembled mitogenome was 14618 bp in length, including 13 protein-coding genes (PCGs), two ribosomal RNA genes, and 22 transfer RNA genes. The overall base composition of P. elegans mitogenome is 32.1% for A, 13.5% for C, 15.7% for G, and 38.7% for T. The gene order was identical to other Phyllidiid species. Phylogenetic analysis placed P. elegans and Phyllidia oecllata in one clade.

Bacterial diversity in the clarki ecotype of the photosynthetic sacoglossan, Elysia crispata.

Few studies have examined the bacterial communities associated with photosynthetic sacoglossan sea slugs. In this study, we determined the bacterial diversity in the clarki ecotype, Elysia crispata using 16S rRNA sequencing. Computational analysis using QIIME2 revealed variability between individual samples, with the Spirochaetes and Bacteroidetes phyla dominating most samples. Tenericutes and Proteobacteria were also found, among other phyla. Computational metabolic profiling of the bacteria revealed a variety of metabolic pathways involving carbohydrate metabolism, lipid metabolism, nucleotide metabolism, and amino acid metabolism. Although associated bacteria may be involved in mutually beneficial metabolic pathways, there was a high degree of variation in the bacterial community of individual slugs. This suggests that many of these relationships are likely opportunistic rather than obligate and that many of these bacteria may live commensally providing no major benefit to the slugs.

A tale of two genera: the revival of Hoplodoris (Nudibranchia: Discodorididae) with the description of new species of Hoplodoris and Asteronotus.

Nudibranchs in the family Discodorididae are generally medium (~30mm) to large ( 50mm) in size, sometimes cryptic, and are found in almost every marine ecosystem around the world. The diversity and systematics of the genera within Discodorididae are poorly understood and have led to numerous taxonomic changes. Hoplodoris Bergh, 1880 has recently been considered a synonym of Asteronotus Ehrenberg, 1831; however, morphological and molecular phylogenetic analyses reveal a distinct separation between these two genera. Here we provide a re-description of the type species Hoplodoris desmoparypha as well as descriptions of four undescribed species of Asteronotus and Hoplodoris. Bayesian inference and maximum likelihood analyses of two mitochondrial and two nuclear genes were used to evaluate the phylogenetic positions of the new species and clarify the relationships between Asteronotus and Hoplodoris to the rest of the Discodorididae. Based on our results, Hoplodoris is removed from synonymy with Asteronotus. Descriptions for Asteronotus markaensis sp. nov., and Asteronotus namuro sp. nov. from the Red Sea, as well as Hoplodoris balbon sp. nov. and Hoplodoris rosans sp. nov. from the western Pacific are provided.

Adding stars to the Chromodoris (Nudibranchia, Chromodorididae) galaxy with the description of four new species.

This paper describes four new Chromodoris species: Chromodoris balat sp. nov., Chromodoris baqe sp. nov., Chromodoris kalawakan sp. nov., and Chromodoris quagga sp. nov. We were able to distinguish 44 species level lineages within Chromodoris, expanding the Indo-Pacific species from 39 species. The phylogeny presented here provides slightly greater resolution of species relationships than do previous studies of this genus. Layton et al. (2018), determined that variable color patterns made it difficult to differentiate in living specimens of distinct species, but we provide some additional stable color characters that potentially help resolve this issue, as well as additional internal features that are useful in species delimitation and correlate with the molecular phylogenetic analysis.

Morphological and molecular evidence of a new species of Melanochlamys (Gastropoda: Heterobranchia) from the Bohai Sea, China.

Increasing discoveries of new species of the genus Melanochlamys Cheeseman, 1881 in the recent years indicate that the biodiversity of this group remains underestimated. Recently, several aglajid sea slugs were collected from Laizhou Bay, Shandong Province, China. Morphological observation of their external and internal anatomy revealed that they represent an undescribed species of Melanochlamys. This new species, Melanochlamys aquilina sp. nov., is closely related to Melanochlamys fukudai Cooke, Hanson, Hirano, Ornelas-Gatdula, Gosliner, Chernyshev Valdés, 2014 in body size and dark external coloration, but can be differentiated from the latter by features of both shell and male reproductive organ. Phylogenetic analyses of two mitochondrial (COI, 16S rRNA) and a nuclear (H3) genes using Bayesian inference, maximum likelihood, and species delimitation analysis also support the separation of Melanochlamys aquilina sp. nov. from its related congeners.

Aplysqualenols A and B: Squalene-Derived Polyethers with Antitumoral and Antiviral Activity from the Caribbean Sea Slug Aplysia dactylomela.

The novel bromotriterpene polyethers aplysqualenol A (1) and aplysqualenol B (2) have been isolated from the Caribbean sea slug Aplysia dactylomela collected in Puerto Rico, and their structures and relative configurational assignments established from spectroscopic data aided by quantum mechanical calculations of NMR chemical shifts. Although both these compounds may be conceived as polyoxycyclic derivatives of the C30 squalene skeleton, remarkably 1 and 2 possess an unprecedented C15 to C24 flexible chain of 14S* spatial disposition that contains a unique ether bridge between C16 and C19. Biological activity screening tests revealed that, although aplysqualenol A (1) does not have significant anti-infective properties, it possesses potent antitumoral and antiviral activities.

Fish-Parasitic Gnathiid Isopods Metamorphose Following Invertebrate-Derived Meal.

Organisms with a parasitic lifestyle comprise a high proportion of biodiversity in aquatic and terrestrial environments. However, there is considerable variation in the ways in which they acquire nutrients. Hematophagy is a common consumption strategy utilized by some terrestrial, aquatic, and marine organisms whereby the parasite removes and digests blood from a host. Gnathiid isopods are marine hematophagous parasites that live in benthic substrates from the intertidal to the abyss. Although ecologically similar to ticks and mosquitoes, they feed only during each of 3 juvenile stages and adults do not feed. They have long been considered as generalist fish parasites and to date, there have been no reports of their successfully feeding on invertebrates. Based on observations of gnathiids attached to soft-bodied invertebrates collected from light traps, we conducted a laboratory experiment in which we collected and individually housed various common Caribbean invertebrates and placed them in containers with gnathiids to see if the gnathiids would feed on them. All fed gnathiids were subsequently removed from containers and given the opportunity to metamorphose to the next developmental stage. In total, 10 out of the 260 gnathiids that were presented with 1 of 4 species of potential invertebrate hosts had fed by the next morning. Specifically, 9 of a possible 120 gnathiids fed on lettuce sea slugs (Elysia crispata), and 1 of a possible 20 fed on a bearded fireworm (Hermodice carunculata). Eight of these 10 fed gnathiids metamorphosed to the next stage (5 to adult male, 2 to adult female, and 1 to third-stage juvenile). Even though feeding rates on invertebrates were considerably lower than observed for laboratory studies on fishes, this study provides the first documented case of gnathiids' feeding on and metamorphosing from invertebrate meals. These findings suggest that when fish hosts are not readily available, gnathiids could switch to soft-bodied invertebrates. They further provide insights into the evolution of feeding on fluids from live hosts in members of this family.

Glossing over cryptic species: Descriptions of four new species of Glossodoris and three new species of Doriprismatica (Nudibranchia: Chromodorididae).

Advances in molecular systematics have led to a rapid increase in the identification of cryptic and pseudocryptic species in organisms exhibiting diverse and complex coloration with complicated taxonomic histories. A recent molecular phylogenetic analysis of nudibranchs in the genus Glossodoris (Mollusca: Gastropoda: Heterobranchia: Chromodorididae) and related genera identifies multiple cryptic and pseudocryptic species complexes, one within Glossodoris pallida and three within Glossodoris cincta, and support for three new species of Doriprismatica. Morphological analyses of color pattern, radular structure, buccal mass, and reproductive system support these identifications. Descriptions for Glossodoris buko sp. nov., Glossodoris bonwanga sp. nov., Glossodoris andersonae sp. nov., Glossodoris acosti sp. nov., and what will retain the name Glossodoris sp. cf. cincta are provided here, in addition to descriptions for new species Doriprismatica balut sp. nov., Doriprismatica rossi sp. nov., and Doriprismatica marinae sp. nov.. Glossodoris pallida and G. buko exhibit extreme differences in radular structure in addition to a clear biogeographic split in range. Glossodoris bonwanga, G. andersonae, G. acosti and G. sp. cf. cincta, share morphological and geographic differences but these are not as pronounced as in G. pallida and G. buko. More detailed study of the G. cincta complex is necessary to resolve some remaining systematic challenges. Doriprismatica balut is clearly distinct from all other congeners based on molecular and morphological characters. In contrast, D. rossi and D. marinae are not strongly divergent genetically, but have major morphological divergences that clearly distinguish them.

Characterization of the complete mitochondrial genome of Melibe japonica (Eliot, 1913) collected from Korean water.

Melibe japonica is the rarely identified nudibranch species in Korean and Japanese waters. Total mitochondrial genome of M. japonica collected from the coastal water of Busan, Korea, was determined by the bioinformatic assembly of the contigs generated by Illumina Miseq platform. The circular complete mitochondrial genome of M. japonica was 13, 216 bp in length, which contains 13 proteins, 2 ribosomal RNAs, and 22 tRNAs. Mitochondrial gene order of M. japonica is considerably different from the mitochondrial genome of Melibe leonina in which 6 genes (ND1, COX2, CYTB, ND4L, ND5, and ND6) were differently located. Phylogenetic analysis with COI regions showed that M. japonica is most closely related to Melibe viridis. However, not all Melibe species formed a single clade based on the phylogenetic analysis by COI region and more mitochondrial genomes in this genus should be further studied to have a better knowledge of the evolutional relationship of the nudibranchs.

The complete mitochondrial genome of the Oriental sea slug: Chromodoris orientalis (Nudibranchia, Chromodorididae).

The mitogenome sequence of sea slug, Chromodoris orientalis (Nudibranchia, Chromodorididae), has been decoded for the first time by coverage genome sequencing method. The overall base composition of C. orientalis mitogenome is 30.5% for A, 14.7% for C, 18.0% for G and 36.9% for T, and has low GC content 32.6%. The assembled mitogenome, consisting of 14,266 bp, has unique 13 protein-coding genes, 22 transfer RNAs, and two ribosomal RNAs genes. The C. orientalis mitogenome has the common mitogenome gene order and feature of Nudipleura (a clade of sea slugs and sea snails). The complete mitogenome of C. orientalis provides essential and important DNA molecular data for further phylogenetic and evolutionary analysis for sea slugs and sea snails.