Why is there no service to support taxonomy?

Increasing complexity and specialisation of modern sciences has led to increasingly collaborative publications, as well as the involvement of commercial services. Modern integrative taxonomy likewise depends on many lines of evidence and is increasingly complex, but the trend of collaboration lags and various attempts at 'turbo taxonomy' have been unsatisfactory. We are developing a taxonomic service in the Senckenberg Ocean Species Alliance to provide fundamental data for new species descriptions. This will also function as a hub to connect a global network of taxonomists, assembling an alliance of scientists working on potential new species to tackle both the extinction and inclusion crises we face today. The current rate of new species descriptions is simply too slow; the discipline is often dismissed as old fashioned, and there is a crisis level need for taxonomic descriptions to come to grips with the scale of Anthropocene biodiversity loss. Here, we envision how the process of describing and naming species would benefit from a service supporting the acquisition of descriptive data. Also see the video abstract here: https://youtu.be/E8q3KJor_F8.

Insights into the genome of the 'Loco' Concholepas concholepas (Gastropoda: Muricidae) from low-coverage short-read sequencing: genome size, ploidy, transposable elements, nuclear RNA gene operon, mitochondrial genome, and phylogenetic placement in the family Muricidae.

BACKGROUND: The Peruvian 'chanque' or Chilean 'loco' Concholepas concholepas is an economically, ecologically, and culturally important muricid gastropod heavily exploited by artisanal fisheries in the temperate southeastern Pacific Ocean. In this study, we have profited from a set of bioinformatics tools to recover important biological information of C. concholepas from low-coverage short-read NGS datasets. Specifically, we calculated the size of the nuclear genome, ploidy, and estimated transposable elements content using an in silico k-mer approach, we discovered, annotated, and quantified those transposable elements, we assembled and annotated the 45S rDNA RNA operon and mitochondrial genome, and we confirmed the phylogenetic position of C. concholepas within the muricid subfamily Rapaninae based on translated protein coding genes. RESULTS: Using a k-mer approach, the haploid genome size estimated for the predicted diploid genome of C. concholepas varied between 1.83 Gbp (with kmer = 24) and 2.32 Gbp (with kmer = 36). Between half and two thirds of the nuclear genome of C. concholepas was composed of transposable elements. The most common transposable elements were classified as Long Interspersed Nuclear Elements and Short Interspersed Nuclear Elements, which were more abundant than DNA transposons, simple repeats, and Long Terminal Repeats. Less abundant repeat elements included Helitron mobile elements, 45S rRNA DNA, and Satellite DNA, among a few others.The 45S rRNA DNA operon of C. concholepas that encodes for the ssrRNA, 5.8S rRNA, and lsrRNA genes was assembled into a single contig 8,090 bp long. The assembled mitochondrial genome of C. concholepas is 15,449 bp long and encodes 13 protein coding genes, two ribosomal genes, and 22 transfer RNAs. CONCLUSION: The information gained by this study will inform the assembly of a high quality nuclear genome for C. concholepas and will support bioprospecting and biomonitoring using environmental DNA to advance development of conservation and management plans in this overexploited marine snail.

Assessing the extinction risk of insular, understudied marine species.

Hydrothermal vents are rare deep-sea oases that house faunal assemblages with a similar density of life as coral reefs. Only approximately 600 of these hotspots are known worldwide, most only one-third of a football field in size. With advancing development of the deep-sea mining industry, there is an urgent need to protect these unique, insular ecosystems and their specialist endemic faunas. We applied the IUCN (International Union for the Conservation of Nature) Red List criteria to assess the extinction risk of vent-endemic molluscs with varying exposure to potential deep-sea mining. We assessed 31 species from three key areas under different regulatory frameworks in the Indian, West Pacific, and Southern Oceans. Three vent mollusc species were also examined as case studies of different threat contexts (protected or not from potential mining) to explore the interaction of local regulatory frameworks and IUCN Red List category assignment. We found that these assessments were robust even when there was some uncertainty in the total range of individual species, allowing assessment of species that have only recently been named and described. For vent-endemic species, regulatory changes to area-based management can have a greater impact on IUCN Red List assessment outcomes than incorporating additional data about species distributions. Our approach revealed the most useful IUCN Red List criteria for vent-endemic species: criteria B and D2. This approach, combining regulatory framework and distribution, has the potential to rapidly gauge assessment outcomes for species in insular systems worldwide.

Evaluación del Riesgo de Extinción de Especies Marinas Insulares Poco Estudiadas Resumen Los respiraderos hidrotermales son oasis poco comunes en las profundidades del mar en donde se encuentran conjuntos de fauna con una densidad similar a la de los arrecifes de coral. A nivel mundial, sólo se conocen aproximadamente 600 de estos puntos calientes, la mayoría solamente del tamaño de un tercio de una cancha de fútbol. Conforme avanza el desarrollo de la industria minera en mares profundos, también hay una urgente necesidad por proteger estos ecosistemas únicos e insulares y a su fauna endémica especialista. Aplicamos el criterio de la Lista Roja de la UICN (Unión Internacional para la Conservación de la Naturaleza) para evaluar el riesgo de extinción que tienen los moluscos endémicos de los respiraderos ante una exposición variable a la potencial minería de mar profundo. Evaluamos 31 especies de tres áreas importantes bajo diferentes marcos regulatorios en los océanos Índico, Pacífico Occidental y del Sur. Analizamos tres especies de moluscos de los respiraderos como estudios de caso para diferentes contextos de amenazas (protegidas o no de la minería potencial) para explorar la interacción de los marcos regulatorios locales y la clasificación categórica dentro de la Lista Roja de la UICN. Descubrimos que estos análisis eran sólidos incluso cuando existía algo de incertidumbre en cuanto a la extensión total de la especie individual, lo que permite la valoración de especies que han sido descritas y nombradas recientemente. Para las especies endémicas de las chimeneas, los cambios regulatorios a un manejo basado en el área pueden tener un mayor impacto sobre los resultados de evaluación de la Lista Roja de la UICN que la incorporación de datos adicionales sobre la distribución de las especies. Nuestra estrategia reveló los criterios más útiles de la Lista Roja de la UICN para las especies endémicas de las chimeneas: los criterios B y D2. Esta estrategia, que combina un marco regulatorio con la distribución, tiene el potencial para medir rápidamente los resultados de las evaluaciones para las especies que se encuentran en sistemas insulares en todo el mundo.

Unlocking the potential of marine biodiscovery.

The tremendous diversity of life in the ocean has proven to be a rich source of inspiration for drug discovery, with success rates for marine natural products up to 4 times higher than other naturally derived compounds. Yet the marine biodiscovery pipeline is characterized by chronic underfunding, bottlenecks and, ultimately, untapped potential. For instance, a lack of taxonomic capacity means that, on average, 20 years pass between the discovery of new organisms and the formal publication of scientific names, a prerequisite to proceed with detecting and isolating promising bioactive metabolites. The need for "edge" research that can spur novel lines of discovery and lengthy high-risk drug discovery processes, are poorly matched with research grant cycles. Here we propose five concrete pathways to broaden the biodiscovery pipeline and open the social and economic potential of the ocean genome for global benefit: (1) investing in fundamental research, even when the links to industry are not immediately apparent; (2) cultivating equitable collaborations between academia and industry that share both risks and benefits for these foundational research stages; (3) providing new opportunities for early-career researchers and under-represented groups to engage in high-risk research without risking their careers; (4) sharing data with global networks; and (5) protecting genetic diversity at its source through strong conservation efforts. The treasures of the ocean have provided fundamental breakthroughs in human health and still remain under-utilised for human benefit, yet that potential may be lost if we allow the biodiscovery pipeline to become blocked in a search for quick-fix solutions.

Moving conferences online: lessons learned from an international virtual meeting.

We consider the opportunities and challenges associated with organizing a conference online, using a case study of a medium-sized (approx. 400 participants) international conference held virtually in August 2020. In addition, we present quantifiable evidence of the participants' experience using the results from an online post-conference questionnaire. Although the virtual meeting was not able to replicate the in-person experience in some aspects (e.g. less engagement between participants) the overwhelming majority of respondents found the meeting an enjoyable experience and would join similar events again. Notably, there was a strong desire for future in-person meetings to have at least some online component. Online attendance by lower-income researchers was higher compared with a past, similar-themed in-person meeting held in a high-income nation, but comparable to one held in an upper-middle-income nation. This indicates that online conferences are not a panacea for diversity and inclusivity, and that holding in-person meetings in developing economies can be at least as effective. Given that it is now relatively easy to stream contents of meetings online using low-cost methods, there are clear benefits in making all presented content accessible online, as well as organizing online networking events for those unable to attend in person.

Seagrass-driven changes in carbonate chemistry enhance oyster shell growth.

Quantifying the strength of non-trophic interactions exerted by foundation species is critical to understanding how natural communities respond to environmental stress. In the case of ocean acidification (OA), submerged marine macrophytes, such as seagrasses, may create local areas of elevated pH due to their capacity to sequester dissolved inorganic carbon through photosynthesis. However, although seagrasses may increase seawater pH during the day, they can also decrease pH at night due to respiration. Therefore, it remains unclear how consequences of such diel fluctuations may unfold for organisms vulnerable to OA. We established mesocosms containing different levels of seagrass biomass (Zostera marina) to create a gradient of carbonate chemistry conditions and explored consequences for growth of juvenile and adult oysters (Crassostrea gigas), a non-native species widely used in aquaculture that can co-occur, and is often grown, in proximity to seagrass beds. In particular, we investigated whether increased diel fluctuations in pH due to seagrass metabolism affected oyster growth. Seagrasses increased daytime pH up to 0.4 units but had little effect on nighttime pH (reductions less than 0.02 units). Thus, both the average pH and the amplitude of diel pH fluctuations increased with greater seagrass biomass. The highest seagrass biomass increased oyster shell growth rate (mm day-1) up to 40%. Oyster somatic tissue weight and oyster condition index exhibited a different pattern, peaking at intermediate levels of seagrass biomass. This work demonstrates the ability of seagrasses to facilitate oyster calcification and illustrates how non-trophic metabolic interactions can modulate effects of environmental change.

High Abundances of Microplastic Pollution in Deep-Sea Sediments: Evidence from Antarctica and the Southern Ocean.

Plastic pollution in Antarctica and the Southern Ocean has been recorded in scientific literature since the 1980s; however, the presence of microplastic particles (<5 mm) is less understood. Here, we aimed to determine whether microplastic accumulation would vary among Antarctic and Southern Ocean regions through studying 30 deep-sea sediment cores. Additionally, we aimed to highlight whether microplastic accumulation was related to sample depth or the sediment characteristics within each core. Sediment cores were digested and separated using a high-density sodium polytungstate solution (SPT) and microplastic particles were identified using micro-Fourier-transform infrared spectroscopy (µFTIR). Microplastic pollution was found in 93% of the sediment cores (28/30). The mean (±SE) microplastics per gram of sediment was 1.30 ± 0.51, 1.09 ± 0.22, and 1.04 ± 0.39 MP/g, for the Antarctic Peninsula, South Sandwich Islands, and South Georgia, respectively. Microplastic fragment accumulation correlated significantly with the percentage of clay within cores, suggesting that microplastics have similar dispersion behavior to low density sediments. Although no difference in microplastic abundance was found among regions, the values were much higher in comparison to less remote ecosystems, suggesting that the Antarctic and Southern Ocean deep-sea accumulates higher numbers of microplastic pollution than previously expected.

Why do chitons curl into a ball?

Many animals with external armour, such as hedgehogs, isopods and trilobites, curl into a protective ball when disturbed. However, in situations where predators would engulf an exposed animal whole, regardless of position, conglobation may provide limited added defence and the benefits were previously unclear. We show that polyplacophoran molluscs (chitons) are three times less likely to spend time curled into a ball in the presence of a predator. When the cue of a potential predator is present, animals instead spend significantly more time in active, high risk, high reward behaviours such as arching, balancing on the head and tail ends of their girdle and pushing the soft foot up into an exposed position. Arching increases vulnerability, but also can increase the likelihood of rapidly encountering new substratum that would allow the animal to right itself. In some other animals, the ability to roll into a ball is associated with rolling away from danger. Curling into a ball would improve mobility, to be rolled on to a safer position, but reattachment is the higher priority for chitons in the face of danger.

Cryptic niche switching in a chemosymbiotic gastropod.

Life stages of some animals, including amphibians and insects, are so different that they have historically been seen as different species. 'Metamorphosis' broadly encompasses major changes in organism bodies and, importantly, concomitant shifts in trophic strategies. Many marine animals have a biphasic lifestyle, with small pelagic larvae undergoing one or more metamorphic transformations before settling into a permanent, adult morphology on the benthos. Post-settlement, the hydrothermal vent gastropod Gigantopelta chessoia experiences a further, cryptic metamorphosis at body sizes around 5-7 mm. The terminal adult stage is entirely dependent on chemoautotrophic symbionts; smaller individuals do not house symbionts and presumably depend on grazing. Using high-resolution X-ray microtomography to reconstruct the internal organs in a growth series, we show that this sudden transition in small but sexually mature individuals dramatically reconfigures the organs, but is in no way apparent from external morphology. We introduce the term 'cryptometamorphosis' to identify this novel phenomenon of a major body change and trophic shift, not related to sexual maturity, transforming only the internal anatomy. Understanding energy flow in ecosystems depends on the feeding ecology of species; the present study highlights the possibility for adult animals to make profound shifts in biology that influence energy dynamics.

Whole-body photoreceptor networks are independent of 'lenses' in brittle stars.

Photoreception and vision are fundamental aspects of animal sensory biology and ecology, but important gaps remain in our understanding of these processes in many species. The colour-changing brittle star Ophiocoma wendtii is iconic in vision research, speculatively possessing a unique whole-body visual system that incorporates information from nerve bundles underlying thousands of crystalline 'microlenses'. The hypothesis that these might form a sophisticated compound eye-like system regulated by chromatophores has been extensively reiterated, with investigations into biomimetic optics and similar supposedly 'visual' structures in living and fossil taxa. However, no photoreceptors or visual behaviours have ever been identified. We present the first evidence of photoreceptor networks in three Ophiocoma species, both with and without microlenses and colour-changing behaviour. High-resolution microscopy, immunohistochemistry and synchrotron tomography demonstrate that putative photoreceptors cover the animals' oral, lateral and aboral surfaces, but are absent at the hypothesized focal points of the microlenses. The structural optics of these crystal 'lenses' are an exaptation and do not fulfil any apparent visual role. This contradicts previous studies, yet the photoreceptor network in Ophiocoma appears even more widespread than previously anticipated, both taxonomically and anatomically.

A Silurian armoured aplacophoran and implications for molluscan phylogeny.

The Mollusca is one of the most diverse, important and well-studied invertebrate phyla; however, relationships among major molluscan taxa have long been a subject of controversy. In particular, the position of the shell-less vermiform Aplacophora and its relationship to the better-known Polyplacophora (chitons) have been problematic: Aplacophora has been treated as a paraphyletic or monophyletic group at the base of the Mollusca, proximate to other derived clades such as Cephalopoda, or as sister group to the Polyplacophora, forming the clade Aculifera. Resolution of this debate is required to allow the evolutionary origins of Mollusca to be reconstructed with confidence. Recent fossil finds support the Aculifera hypothesis, demonstrating that the Palaeozoic-era palaeoloricate 'chitons' included taxa combining certain polyplacophoran and aplacophoran characteristics. However, fossils combining an unambiguously aplacophoran-like body with chiton-like valves have remained elusive. Here we describe such a fossil, Kulindroplax perissokomos gen. et sp. nov., from the Herefordshire Lagerstätte (about 425 million years bp), a Silurian deposit preserving a marine biota in unusual three-dimensional detail. The specimen is reconstructed three-dimensionally through physical-optical tomography. Phylogenetic analysis indicates that this and many other palaeoloricate chitons are crown-group aplacophorans.

By more ways than one: Rapid convergence at hydrothermal vents shown by 3D anatomical reconstruction of Gigantopelta (Mollusca: Neomphalina).

BACKGROUND: Extreme environments prompt the evolution of characteristic adaptations. Yet questions remain about whether radiations in extreme environments originate from a single lineage that masters a key adaptive pathway, or if the same features can arise in parallel through convergence. Species endemic to deep-sea hydrothermal vents must accommodate high temperature and low pH. The most successful vent species share a constrained pathway to successful energy exploitation: hosting symbionts. The vent-endemic gastropod genus Gigantopelta, from the Southern and Indian Oceans, shares unusual features with a co-occurring peltospirid, the 'scaly-foot gastropod' Chrysomallon squamiferum. Both are unusually large for the clade and share other adaptive features such as a prominent enlarged trophosome-like oesophageal gland, not found in any other vent molluscs. RESULTS: Transmission electron microscopy confirmed endosymbiont bacteria in the oesophageal gland of Gigantopelta, as also seen in Chrysomallon. They are the only known members of their phylum in vent ecosystems hosting internal endosymbionts; other vent molluscs host endosymbionts in or on their gills, or in the mantle cavity. A five-gene phylogenetic reconstruction demonstrated that Gigantopelta and Chrysomallon are not phylogenetically sister-taxa, despite their superficial similarity. Both genera have specialist adaptations to accommodate internalised endosymbionts, but with anatomical differences that indicate separate evolutionary origins. Hosting endosymbionts in an internal organ within the host means that all resources required by the bacteria must be supplied by the animal, rather than directly by the vent fluid. Unlike Chrysomallon, which has an enlarged oesophageal gland throughout post-settlement life, the oesophageal gland in Gigantopelta is proportionally much smaller in juveniles and the animals likely undergo a trophic shift during ontogeny. The circulatory system is hypertrophied in both but the overall size is smaller in Gigantopelta. In contrast with Chrysomallon, Gigantopelta possesses true ganglia and is gonochoristic. CONCLUSIONS: Key anatomical differences between Gigantopelta and Chrysomallon demonstrate these two genera acquired a similar way of life through independent and convergent adaptive pathways. What appear to be the holobiont's adaptations to an extreme environment, are driven by optimising bacteria's access to vent nutrients. By comparing Gigantopelta and Chrysomallon, we show that metazoans are capable of rapidly and repeatedly evolving equivalent anatomical adaptations and close-knit relationships with chemoautotrophic bacteria, achieving the same end-product through parallel evolutionary trajectories.

Consensus and confusion in molluscan trees: evaluating morphological and molecular phylogenies.

Mollusks are the most morphologically disparate living animal phylum, they have diversified into all habitats, and have a deep fossil record. Monophyly and identity of their eight living classes is undisputed, but relationships between these groups and patterns of their early radiation have remained elusive. Arguments about traditional morphological phylogeny focus on a small number of topological concepts but often without regard to proximity of the individual classes. In contrast, molecular studies have proposed a number of radically different, inherently contradictory, and controversial sister relationships. Here, we assembled a data set of 42 unique published trees describing molluscan interrelationships. We used these data to ask several questions about the state of resolution of molluscan phylogeny compared with a null model of the variation possible in random trees constructed from a monophyletic assemblage of eight terminals. Although 27 different unique trees have been proposed from morphological inference, the majority of these are not statistically different from each other. Within the available molecular topologies, only four studies to date have included the deep sea class Monoplacophora; but 36.4% of all trees are not significantly different. We also present supertrees derived from two data partitions and three methods, including all available molecular molluscan phylogenies, which will form the basis for future hypothesis testing. The supertrees presented here were not constructed to provide yet another hypothesis of molluscan relationships, but rather to algorithmically evaluate the relationships present in the disparate published topologies. Based on the totality of available evidence, certain patterns of relatedness among constituent taxa become clear. The internodal distance is consistently short between a few taxon pairs, particularly supporting the relatedness of Monoplacophora and the chitons, Polyplacophora. Other taxon pairs are rarely or never found in close proximity, such as the vermiform Caudofoveata and Bivalvia. Our results have specific utility for guiding constructive research planning to better test relationships in Mollusca as well as other problematic groups. Taxa with consistently proximate relationships should be the focus of a combined approach in a concerted assessment of potential genetic and anatomical homology, whereas unequivocally distant taxa will make the most constructive choices for exemplar selection in higher level phylogenomic analyses.

A neurophylogenetic approach provides new insight to the evolution of Scaphopoda.

The position of scaphopods in molluscan phylogeny remains singularly contentious, with several sister relationships supported by morphological and phylogenomic data: Scaphopoda + Bivalvia (Diasoma), Scaphopoda + Cephalopoda (Variopoda), and Scaphopoda + Gastropoda. Nervous system architecture has contributed significant insights to reconstructing phylogeny in the Mollusca and other invertebrate groups, but a modern neurophylogenetic approach has not been applied to molluscs, hampered by a lack of clearly defined homologous characters that can be unequivocally compared across the radical body plan disparity among the living clades. We present the first three-dimensional reconstruction of the anterior nervous system of a scaphopod, Rhabdus rectius, using histological tomography. We also describe a new putative sensory organ, a paired and pigmented sensory mantle slit. This structure is restricted to our study species and not a general feature of scaphopods, but it forms an integral part of the description of the nervous system in R. rectius. It also highlights the potential utility of neuro-anatomical characters for multiple levels of phylogenetic inference beyond this study. This potential has not previously been exploited for the thorny problem of molluscan phylogeny. The neuroanatomy of scaphopods demonstrates a highly derived architecture that shares a number of key characters with the cephalopod nervous system, and supports a Scaphopoda + Cephalopoda grouping.

The heart of a dragon: 3D anatomical reconstruction of the 'scaly-foot gastropod' (Mollusca: Gastropoda: Neomphalina) reveals its extraordinary circulatory system.

INTRODUCTION: The 'scaly-foot gastropod' (Chrysomallon squamiferum Chen et al., 2015) from deep-sea hydrothermal vent ecosystems of the Indian Ocean is an active mobile gastropod occurring in locally high densities, and it is distinctive for the dermal scales covering the exterior surface of its foot. These iron-sulfide coated sclerites, and its nutritional dependence on endosymbiotic bacteria, are both noted as adaptations to the extreme environment in the flow of hydrogen sulfide. We present evidence for other adaptations of the 'scaly-foot gastropod' to life in an extreme environment, investigated through dissection and 3D tomographic reconstruction of the internal anatomy. RESULTS: Our anatomical investigations of juvenile and adult specimens reveal a large unganglionated nervous system, a simple and reduced digestive system, and that the animal is a simultaneous hermaphrodite. We show that Chrysomallon squamiferum relies on endosymbiotic bacteria throughout post-larval life. Of particular interest is the circulatory system: Chrysomallon has a very large ctenidium supported by extensive blood sinuses filled with haemocoel. The ctenidium provides oxygen for the host but the circulatory system is enlarged beyond the scope of other similar vent gastropods. At the posterior of the ctenidium is a remarkably large and well-developed heart. Based on the volume of the auricle and ventricle, the heart complex represents approximately 4 % of the body volume. This proportionally giant heart primarily sucks blood through the ctenidium and supplies the highly vascularised oesophageal gland. Thus we infer the elaborate cardiovascular system most likely evolved to oxygenate the endosymbionts in an oxygen poor environment and/or to supply hydrogen sulfide to the endosymbionts. CONCLUSIONS: This study exemplifies how understanding the autecology of an organism can be enhanced by detailed investigation of internal anatomy. This gastropod is a large and active species that is abundant in its hydrothermal vent field ecosystem. Yet all of its remarkable features-protective dermal sclerites, circulatory system, high fecundity-can be viewed as adaptations beneficial to its endosymbiont microbes. We interpret these results to show that, as a result of specialisation to resolve energetic needs in an extreme chemosynthetic environment, this dramatic dragon-like species has become a carrying vessel for its bacteria.

Anthropogenic noise affects behavior across sensory modalities.

Many species are currently experiencing anthropogenically driven environmental changes. Among these changes, increasing noise levels are specifically a problem for species using acoustic signals (i.e., species relying on signals that use the same sensory modality as anthropogenic noise). Yet many species use other sensory modalities, such as visual and olfactory signals, to communicate. However, we have only little understanding of whether changes in the acoustic environment affect species that use sensory modalities other than acoustic signals. We studied the impact of anthropogenic noise on the common cuttlefish Sepia officinalis, which uses highly complex visual signals. We showed that cuttlefish adjusted their visual displays by changing their color more frequently during a playback of anthropogenic noise, compared with before and after the playback. Our results provide experimental evidence that anthropogenic noise has a marked effect on the behavior of species that are not reliant on acoustic communication. Thus, interference in one sensory channel, in this case the acoustic one, affects signaling in other sensory channels. By considering sensory channels in isolation, we risk overlooking the broader implications of environmental changes for the behavior of animals.

A new sensory organ in "primitive" molluscs (Polyplacophora: Lepidopleurida), and its context in the nervous system of chitons.

INTRODUCTION: Chitons (Polyplacophora) are molluscs considered to have a simple nervous system without cephalisation. The position of the class within Mollusca is the topic of extensive debate and neuroanatomical characters can provide new sources of phylogenetic data as well as insights into the fundamental biology of the organisms. We report a new discrete anterior sensory structure in chitons, occurring throughout Lepidopleurida, the order of living chitons that retains plesiomorphic characteristics. RESULTS: The novel "Schwabe organ" is clearly visible on living animals as a pair of streaks of brown or purplish pigment on the roof of the pallial cavity, lateral to or partly covered by the mouth lappets. We describe the histology and ultrastructure of the anterior nervous system, including the Schwabe organ, in two lepidopleuran chitons using light and electron microscopy. The oesophageal nerve ring is greatly enlarged and displays ganglionic structure, with the neuropil surrounded by neural somata. The Schwabe organ is innervated by the lateral nerve cord, and dense bundles of nerve fibres running through the Schwabe organ epithelium are frequently surrounded by the pigment granules which characterise the organ. Basal cells projecting to the epithelial surface and cells bearing a large number of ciliary structures may be indicative of sensory function. The Schwabe organ is present in all genera within Lepidopleurida (and absent throughout Chitonida) and represents a novel anatomical synapomorphy of the clade. CONCLUSIONS: The Schwabe organ is a pigmented sensory organ, found on the ventral surface of deep-sea and shallow water chitons; although its anatomy is well understood, its function remains unknown. The anterior commissure of the chiton oesophagial nerve ring can be considered a brain. Our thorough review of the chiton central nervous system, and particularly the sensory organs of the pallial cavity, provides a context to interpret neuroanatomical homology and assess this new sense organ.

Size matters: plasticity in metabolic scaling shows body-size may modulate responses to climate change.

Variability in metabolic scaling in animals, the relationship between metabolic rate ( R: ) and body mass ( M: ), has been a source of debate and controversy for decades. R: is proportional to MB: , the precise value of B: much debated, but historically considered equal in all organisms. Recent metabolic theory, however, predicts B: to vary among species with ecology and metabolic level, and may also vary within species under different abiotic conditions. Under climate change, most species will experience increased temperatures, and marine organisms will experience the additional stressor of decreased seawater pH ('ocean acidification'). Responses to these environmental changes are modulated by myriad species-specific factors. Body-size is a fundamental biological parameter, but its modulating role is relatively unexplored. Here, we show that changes to metabolic scaling reveal asymmetric responses to stressors across body-size ranges; B: is systematically decreased under increasing temperature in three grazing molluscs, indicating smaller individuals were more responsive to warming. Larger individuals were, however, more responsive to reduced seawater pH in low temperatures. These alterations to the allometry of metabolism highlight abiotic control of metabolic scaling, and indicate that responses to climate warming and ocean acidification may be modulated by body-size.