Relaciones zoogeográficas de Nudibranchia (Mollusca: Opisthobranchia) de Magallanes con referencia especial a las especies de regiones adyacentes

Extensive recent collections and taxonomical revisions provide a basis for the first zoogeographical analysis of Magellan Nudibranchia. Using 36 of 57 nominal species described in this area, the degree of endemism has been decreased from 70% to 31%. Very close faunistic relationships to northern Argentina are evident as five of six known species (83%) are shared with the Magellan Province. With a 43% overlap of Magellan species in the southern part of the Peruvian faunal Province (44 species), this area shows a transitional character between cold- and warm-temperate waters. Only three of 36 Magellan species are found in common with the high Antarctic (ca. 30 species), revealing a low faunal similarity of about 10%. High Antarctic waters are characterized by high nudibranch endemism (about 80%). Of the ten nudibranch species reported from South Georgia, two are exclusively shared with Magellan, two with high Antarctic and three with both Magellan and Antarctic waters, indicating transitional, Subantarctic conditions. One species is endemic to South Georgia, two other species are insufficiently known and may or may not be endemic. Generally, the Antarctic Convergence appears to be a distributional barrier for Magellan nudibranchs. In contrast, some Antarctic nudibranch species extend far into the Atlantic, obviously with cold Antarctic deep water currents. Coastal, cold temperate Magellan nudibranchs have relatively low affinities to the deep water fauna off Argentina, which seems to be predominantly submerged Antarctic species, but this bathymetrical zonation needs to be further investigated.Recolecciones extensivas y revisiones taxonómicas actuales forman la base del primer análisis zoogeográfico de Nudibranchia magallánicos. Utilizando 36 de 57 especies nominales descritas de esta área, el grado de endemismo ha bajado desde 70% a 31%. Existen relaciones faunísticas muy próximas con el norte de Argentina ya que cinco de las seis especies conocidas (83%) son comunes con la Provincia Magallánica. Las especies magallánicas contribuyen 43% de las especies conocidas de la parte sur de la Provincia faunistíca Peruana (44 en total), indicando el carácter de transición de esta área entre aguas templado-frías y cálidas. Sólo tres de 36 especies magallánicas son comunes con zonas al sur de la Convergencia Antártica (ca. 30 especies), resultando una afinidad faunística muy baja, de aproximadamente 10%. Las aguas antárticas se caracterizan por un muy alto nivel de endemismo de nudibranquios (ca. 80%). De las diez especies de nudibranquios citadas en Georgia del Sur, dos son comunes con áreas magallánicas exclusivamente, dos con la Antártida y tres con aguas antárticas y magallánicas, señalando condiciones de transición, subantárticas. Una espécie es endémica de Georgia del Sur, otras dos se conocen de manera deficiente, por lo que existe la posibilidad de que también sean endémicas. En general, la Convergencia Antártica parece un límite distribucional para nudibranquios magallánicos. Sin embargo, algunas especies de nudibranquios antárticos se extienden mucho hacia el Atlántico, obviamente con aguas antárticas profundas. Los nudibranquios magallánicos de las zonas templadas-frías sublitorales tienen relativamente poca afinidad con la fauna del talud argentino, que parece dominada por especies antárticas sumergidas, pero esta zonación batimétrica necesita ser estudiada de forma más extensa en el futuro

Cryptic species in tropic sands--interactive 3D anatomy, molecular phylogeny and evolution of meiofaunal Pseudunelidae (Gastropoda, Acochlidia)

Towards realistic estimations of the diversity of marine animals, tiny meiofaunal species usually are underrepresented. Since the biological species concept is hardly applicable on exotic and elusive animals, it is even more important to apply a morphospecies concept on the best level of information possible, using accurate and efficient methodology such as 3D modelling from histological sections. Molecular approaches such as sequence analyses may reveal further, cryptic species. This is the first case study on meiofaunal gastropods to test diversity estimations from traditional taxonomy against results from modern microanatomical methodology and molecular systematics

How to describe a cryptic species? Practical challenges of molecular taxonomy

Background: Molecular methods of species delineation are rapidly developing and widely considered as fast and efficient means to discover species and face the `taxonomic impediment' in times of biodiversity crisis. So far, however, this form of DNA taxonomy frequently remains incomplete, lacking the final step of formal species description, thus enhancing rather than reducing impediments in taxonomy. DNA sequence information contributes valuable diagnostic characters and - at least for cryptic species-could even serve as the backbone of a taxonomic description. To this end solutions for a number of practical problems must be found, including a way in which molecular data can be presented to fulfill the formal requirements every description must meet. Multi-gene barcoding and a combined molecular species delineation approach recently revealed a radiation of at least 12 more or less cryptic species in the marine meiofaunal slug genus Pontohedyle (Acochlidia, Heterobranchia). All identified candidate species are well delimited by a consensus across different methods based on mitochondrial and nuclear markers. Results: The detailed microanatomical redescription of Pontohedyle verrucosa provided in the present paper does not reveal reliable characters for diagnosing even the two major clades identified within the genus on molecular data. We thus characterize three previously valid Pontohedyle species based on four genetic markers (mitochondrial cytochrome c oxidase subunit I, 16S rRNA, nuclear 28S and 18S rRNA) and formally describe nine cryptic new species (P. kepii sp. nov., P. joni sp. nov., P. neridae sp. nov., P. liliae sp. nov., P. wiggi sp. nov., P. wenzli sp. nov., P. peteryalli sp. nov., P. martynovi sp. nov., P. yurihookeri sp. nov.) applying molecular taxonomy, based on diagnostic nucleotides in DNA sequences of the four markers. Due to the minute size of the animals, entire specimens were used for extraction, consequently the holotype is a voucher of extracted DNA ('DNA-type'). We used the Character Attribute Organization System (CAOS) to determine diagnostic nucleotides, explore the dependence on input data and data processing, and aim for maximum traceability in our diagnoses for future research. Challenges, pitfalls and necessary considerations for applied DNA taxonomy are critically evaluated. Conclusions: To describe cryptic species traditional lines of evidence in taxonomy need to be modified. DNA sequence information, for example, could even serve as the backbone of a taxonomic description. The present contribution demonstrates that few adaptations are needed to integrate into traditional taxonomy novel diagnoses based on molecular data. The taxonomic community is encouraged to join the discussion and develop a quality standard for molecular taxonomy, ideally in the form of an automated final step in molecular species delineation procedures

Origin and significance of two pairs of head tentacles in the radiation of euthyneuran sea slugs and land snails

The gastropod infraclass Euthyneura comprises at least 30,000 species of snails and slugs, including nudibranch sea slugs, sea hares and garden snails, that flourish in various environments on earth. A unique morphological feature of Euthyneura is the presence of two pairs of sensory head tentacles with different shapes and functions: the anterior labial tentacles and the posterior rhinophores or eyestalks. Here we combine molecular phylogenetic and microanatomical evidence that suggests the two pairs of head tentacles have originated by splitting of the original single tentacle pair (with two parallel nerve cords in each tentacle) as seen in many other gastropods. Minute deep-sea snails of Tjaernoeia and Parvaplustrum, which in our phylogeny belonged to the euthyneurans' sister group (new infraclass Mesoneura), have tentacles that are split along much of their lengths but associated nerves and epidermal sense organs are not as specialized as in Euthyneura. We suggest that further elaboration of cephalic sense organs in Euthyneura closely coincided with their ecological radiation and drastic modification of body plans. The monotypic family Parvaplustridae nov., superfamily Tjaernoeioidea nov. (Tjaernoeiidae + Parvaplustridae), and new major clade Tetratentaculata nov. (Mesoneura nov. + Euthyneura) are also proposed based on their phylogenetic relationships and shared morphological traits

Really a “secondary gill under the skin”? Unveiling “dorsal vessels” in freshwater slugs (Mollusca, Panpulmonata, Acochlidimorpha)

The freshwater slugs of the genus Acochlidium (Heterobranchia, Gastropoda, and Acochlidimorpha) are peculiar, one to two centimeter sized animals found only in small coastal rivers and streams of Southeast Asian and Western Pacific islands. When first described by Bücking, the author observed a branching “net of dendritic vessels connected to the heart,” which he assumed to have replaced the original gastropod gill. In the present study, we compare the renopericardial systems of four Acochlidium species in microanatomical, histological and ultrastructural detail and identify where exactly the enigmatic, subepidermal “dorsal vessels” connect to the renopericardial system to examine if they can really function as a gill. Acochlidium have elaborate renopericardial systems compared to their ancestrally marine and also freshwater relatives. The primary site of ultrafiltration is the epicardium of the atrium with podocytes as usual for gastropods. The “dorsal vessels” in Acochlidium are extensions of the outer epithelium of the pericardial cavity and represent true vessels, that is, coelomatic channels, having an endothelium with podocytes. Hence, they considerably enlarge the site of ultrafiltration increasing the pericardial surface. “Dorsal vessels” in Acochlidium are therefore not homologous to externally similar morphological structures in Sacoglossa (marine panpulmonate slugs and snails). The multiplication of renopericardioducts in Acochlidium is a unique feature within Mollusca that enhances the negative pressure necessary for ultrafiltration in the thin, tube-like dorsal vessels and as a consequence the transport of primary urine from the pericardium to the kidney. The circulatory and excretory systems in Acochlidium are adaptations to a lifestyle in their freshwater environment in which snail bodies are hyposmotic and accrue considerable influx of surplus water into the body, which needs to be expelled

Undersized and underestimated: 3D visualization of the Mediterranean interstitial acochlidian gastropod Pontohedyle milaschewitchii (Kowalevsky, 1901)

AbstractPontohedyle milaschewitchii (Kowalevsky, 1901) is one of the most common mesopsammic opisthobranchs in the Mediterranean and Black Seas and has been considered as a comparably well-described acochlidian species. However, data on its complex internal anatomy were fragmentary and little detailed due to inadequate methodology available, and contradictory between different sources. The present study redescribes all major organ systems of P. milaschewitchii in full detail by three-dimensional reconstruction from serial semithin sections using AMIRA software. The prepharyngeal central nervous system (cns) of P. milaschewitchii is highly concentrated and shows a euthyneurous and epiathroid condition. Contrary to earlier reports, the cerebral and pleural ganglia are not fused. Aggregations of precerebral accessory ganglia can be grouped into three complexes supplied by distinct cerebral nerves. Rhinophoral ganglia with thin, double cerebro-rhinophoral connectives are described for the first time in acochlidians. A Hancock's organ is present in the form of a conspicuous, curved fold in the epidermis posterior to the oral tentacles. Cerebral nervous features and sensory structures are discussed comparatively. Our study confirms P. milaschewitchii as having the male genital opening in an unusual position above the mouth. Homology of the ciliated vas deferens of the gonochoristic and aphallic P. milaschewitchii with that of hermaphroditic acochlidian species with cephalic male genitals is discussed. The radula formula of P. milaschewitchii is 41–54×1-1-1, i.e. the single lateral teeth are broad and, contrary to previous descriptions, undivided. SEM examination of the body wall of entire specimens revealed a special and constant ciliary pattern. Providing a novel additional set of characters for taxonomic and phylogenetic purposes, external SEM examination is suggested as the standard method for describing acochlidian species in the future