Key to sessile gnesiotrochan rotifers: Families, monospecific species in Flosculariidae, species of Atrochidae, Conochilidae, and Limnias.

Accurate identification of species is key to understanding their ecological roles and evolutionary history. It is also essential in cataloging biodiversity for comparisons among habitat types, responses to climate change, effective management practices, and more. The paucity of taxonomic expertise is increasing and with it the ability to competently identify species, this is particularly true for small taxa including rotifers. In an effort to improve this situation, we collated information on morphological characters from the literature on all valid species of sessile Gnesiotrocha (phylum Rotifera) currently assigned to two orders and four families. We review Order Collothecaceae, which comprises families Atrochidae (3 spp.) and Collothecidae (50 spp.) and Order Flosculariaceae, which includes families Conochilidae (7 spp.) and Flosculariidae (71 species). Based on that information, we provide dichotomous keys to the Families, monospecific species in Flosculariidae, and species of Atrochidae, Conochilidae, and Limnias. These keys will aid researchers to identify species in these families and lead to a better understanding of freshwater biodiversity and eco-evolutionary processes.

First ultrastructural description of an apomictic opsiblastic egg in freshwater Gastrotricha.

Freshwater gastrotrichs have a biphasic lifecycle that reputedly involves the production of three types of eggs: apomictic and fast hatching (tachyblastic ova), apomictic and delayed hatching (opsiblastic ova), and plaque-bearing eggs (potentially derived from mixis). While some details of oogenesis and eggshell structure are known for tachyblastic ova, there are few details on other egg types. Here, we provide the first ultrastructural description of the oviposited opsiblastic eggs of the freshwater gastrotrich, Lepidodermella squamata. Scanning electron microscopy revealed the eggshell surface to be ornamented with long flattened pillar-like structures centered on polygonal plates that are pitted along their periphery. Transmission electron microscopy showed the pits to lead to a vast labyrinth of tubular spaces and larger cavities throughout the thick apical layer of the shell. The basal layer of the shell is amorphous and connected to a network of fine fibers that traverse an extra-oocyte space and forms a protective sheet around the uncleaved oocyte. The uncleaved oocyte has a dense layer of peripheral ooplasm surrounding a core of organelles including mitochondria, membrane-bound secretion granules, endoplasmic reticulum, and a single nucleus in a granular, ribosome-rich cytoplasm. Secretion granules are the most abundant organelles and presumably contain lipid-rich yolk that will be used as energy for delayed cleavage, thus functioning in temporal dispersal. These data are compared to the fine structure of invertebrate resting eggs across the phylogenetic spectrum to determine the novelty of opsiblastic egg structure in L. squamata.

The high biodiversity of benthic organisms in a coastal ecosystem revealed by an integrative approach / A alta biodiversidade de organismos bentônicos em um ecossistema costeiro revelada por uma abordagem integrativa

Abstract Increasing habitat modification and species loss demand consistent efforts to describe and understand biodiversity patterns. The BIOTA/FAPESP Program was created in this context and it has been a successful initiative to promote studies on biodiversity and conservation in Brazil. The BIOTA/Araçá is an interdisciplinary project that provided a detailed evaluation of the biodiversity of Araçá Bay, a coastal seascape located on the North coast of the state of São Paulo, Southeast Brazil. The bay encompasses multiple habitats, such as beaches, mangroves, rocky shores, and a tidal flat, and provides important ecosystem services. Unfortunately, the bay is the subject of complex social-environmental conflicts that oppose economic, social, and environmental demands (i.e., the expansion of neighboring harbor activities vs. small-scale artisanal fisheries and protection of biodiversity). The present study presents a survey of the benthic species occurring in the different habitats of Araçá Bay, including data obtained during the BIOTA/Araçá project and previous assessments of the area. The benthic species play an important role in marine environments and studying the diversity of these organisms that live associated with the bottom is indispensable for comprehending the environment's functioning. The macrofauna, meiofauna, and microorganisms associated with soft and hard bottom were listed, and additional information, such as the habitat and geographical distribution, were provided for each species. The checklist includes 826 species, almost 70% recorded during the BIOTA/Araçá project. The most speciose taxa were the annelids (225 spp.), mollusks (194 spp.), and crustaceans (177 spp.). Seven benthic species are endemic to Araçá Bay, 14 are considered threatened, and seven are economically exploited. Furthermore, the bay is the type locality of many taxa, and 11 new benthic species were described based on specimens sampled during the project. This project shows the importance of Araçá Bay as a unique biologically rich environment and highlights the need for conservation efforts in light of the current threats.

Resumo O aumento da modificação dos habitats e da perda de espécies demanda esforços consistentes para descrever e compreender os padrões de biodiversidade. O programa BIOTA/FAPESP foi criado nesse contexto e é uma iniciativa de sucesso para promover estudos em biodiversidade e conservação no Brasil. O BIOTA/Araçá é um projeto interdisciplinar que promoveu uma avaliação detalhada da biodiversidade da Baía do Araçá, um ecossistema costeiro localizado ao Norte do estado de São Paulo, Sudeste do Brasil. A baía engloba múltiplos habitats, tais como praias, manguezais, costões rochosos, e uma planície de maré, e também fornece importantes serviços ecossistêmicos. Infelizmente, a baía está sujeita à conflitos sócio-ambientais complexos que contrastam demandas econômicas, sociais e ambientais (i.e. a expansão das atividades do porto vizinho vs. a pesca artesanal de pequena escala e a proteção da biodiversidade). O presente estudo apresenta um levantamento das espécies bentônicas que ocorrem nos diferentes habitats da Baía do Araçá, incluindo dados obtidos durante o projeto BIOTA/Araçá e de investigações realizadas anteriormente na área. As espécies bentônicas desempenham um papel importante no ambiente marinho, e estudar a diversidade desses organismos que vivem associados ao fundo é indispensável para compreender o funcionamento do meio ambiente. A macrofauna, meiofauna, e microorganismos associados aos fundos consolidado e inconsolidado foram listados, e informações adicionais foram fornecidas para cada espécie, tais como a distribuição geográfica e nos habitats. O checklist inclui 826 espécies, quase 70% registradas durante o projeto BIOTA/Araçá. Os taxa mais especiosos foram os anelídeos (225 spp.), moluscos (194 spp.), e crustáceos (177 spp.). Entre as espécies bentônicas listadas, sete são endêmicas da Baía do Araçá, 14 são consideradas ameaçadas de extinção, e sete são exploradas economicamente. A baía é a localidade tipo de vários taxa, e 11 novas espécies bentônicas foram descritas com base em espécimes amostrados durante o projeto. Este projeto mostra a importância da Baía do Araçá como um ambiente de riqueza biológica única e demonstra a necessidade de esforços para a sua conservação considerando as atuais ameaças.

Ultrastructural characterization of the putative defensive glands (warts) in the sessile, colonial rotifer Sinantherina socialis (Gnesiotrocha; Flosculariidae).

Female Sinantherina socialis are freshwater, sessile, colonial rotifers that possess two pairs of distinctive glands (warts) located below the corona. Previous studies demonstrated that colonies are unpalatable to many invertebrate and vertebrate predators; those authors suggested that the warts were a possible source of a chemical deterrent to predation. Here we explore wart ultrastructure and cytochemisty to determine whether the warts function as exocrine glands and if their contents display any allomone-like chemistry, respectively. Externally, the warts appear as elevated bulges without pores. Internally, the warts are specialized regions of the integumental syncytium and therefore acellular. The lipid stain Nile Red labels all four warts. Two lipid membrane probes (sphingomyelin and phosphatidylinositol) also bind the warts and may be staining internal secretion vesicle membranes. In fact, wart ultrastructure is defined by hundreds of membrane-bound secretion vesicles packed tightly together. The vesicles are mostly electron-lucent and crowded into a well-defined cytoplasmic space. The cytoplasm also contains abundant ribosomes, rough endoplasmic reticulum, mitochondria, and Golgi, but nuclei are generally positioned peripheral to the packed vesicles. Absence of muscles around the warts or any signs of direct innervation suggests expulsion of gland contents is forced by general body contraction. A single specimen with 'empty' warts implies that secretions are released en masse from all glands simultaneously. The identity of the chemical secretion remains to be determined, but the lack of osmium and uranyl acetate staining suggests a low abundance or absence of phenols, unsaturated lipids, or NH2 and -COOH groups. This absence, combined with the positive Nile Red staining, is interpreted as evidence that vesicles contain saturated fatty acids such as lactones that are unpalatable to predators.

A new species of Crasiella (Gastrotricha: Planodasyidae) from Capron Shoal, Florida, USA.

A new gastrotrich species of the genus Crasiella (Macrodasyida: Planodasyidae) is described from Capron Shoal, Florida, USA. The new species is up to 520 µm long and differs from its congeners in the position of adhesive tubes and the structure of its spermatozoa. There are nine TbA that insert ventrally on the head plus an additional pair of TBA that insert medially. Up to 42 TbVL per side. Six pairs of TbP insert on a pair of caudal pedicles. Animals are simultaneous hermaphrodites with an elongated frontal organ and large caudal organ. The spermatozoa have a tripartite acrosome unlike others in the genus that have a four-part acrosome.

Elemental Enrichment of the Exoskeleton in Three Species of Tick (Arachnida: Ixodidae).

Three species of adult hard tick (Ixodidae) were examined with scanning electron microscopy-energy dispersive X-ray spectroscopy to obtain elemental profiles of their exoskeletons and determine the presence of trace elements. The scutum, tarsal claws, chelicerae, and hypostome were examined on females and males of Amblyomma americanum, Dermacentor variabilis, and Ixodes scapularis. The only trace elements present included chlorine, calcium, and sodium. Chlorine was the most abundant trace element and occurred in all examined regions. The chelicerae generally possessed the highest weight percentages of Cl (up to 11.32 ± 1.36%) across all 3 species, although high weight percentages of Cl (up to 8.78 ± 2.77%) were also present in the hypostome teeth of most specimens. All 3 trace elements were present in the hypostome of A. americanum and I. scapularis, but Ca and Na appear to be absent from the teeth of D. variabilis. In general, there were few differences in the elemental profiles of the exoskeletons between the sexes of any species. This study confirms the presence of alkali metals (Na) and alkaline earth metals (Ca) in adult ticks, which are also common in other arachnids; however, the absence of transition metals such as zinc from the exoskeletons of ticks is uncommon and only shared with species of Ricinulei and Opiliones.

Fine structure of the subitaneous eggshell of the sessile rotifer Stephanoceros millsii (Monogononta) with observations on vesicle trafficking in the integument during ontogeny.

Rotifers that engage in cyclical parthenogenesis produce two types of eggs: subitaneous eggs that hatch as clonal females and meiotic eggs that hatch as haploid males, or if fertilized, as females after a period of diapause (resting eggs). The ultrastructure of resting eggshells is known for some motile species, but there are limited data on subitaneous eggshells, and no data on any eggshells of sessile rotifers. Here, we investigated the ultrastructure of the subitaneous eggshell of the sessile rotifer Stephanoceros millsii and its potential origins of secretion, the maternal vitellarium and embryonic integument. We also explored secretory activity in the larval and adult integuments to determine whether activity changes during ontogeny. The eggshell consists of a single layer with two sublayers: an external granular sublayer apparently derived from the maternal vitellarium, and an internal flocculent sublayer secreted by the embryonic integument that may form a hatching membrane or glycocalyx. Secretory activity remains high in both the larva and adult and appears to be the source of the thickening glycocalyx. Altogether, the subitaneous eggshell of S. millsii is the thinnest among monogonont rotifers. Thin eggshells may have evolved in response to the added protection provided by the mother's extracorporeal tube.

Integrated data analysis allows the establishment of a new, cosmopolitan genus of marine Macrodasyida (Gastrotricha).

Macrodasyida (phylum Gastrotricha) comprises 365 species distributed across 34 genera and 10 families. However, current classification is under revision due to the contradictory results of molecular and morphological cladistic analyses. Studies aimed at bridging the gaps took advantage of supplementary assessments of poorly known species and particularly from observations of new taxa showing original traits that could help to identify plesiomorphic character states in these anatomically diverse micrometazoa. We follow this path by describing three new interesting macrodasyidan species respectively from Italy, Brazil and Sweden. In many respects, the new species resemble most closely species of the genus Macrodasys; however, details of the external morphology, in combination with the different lay-out of the reproductive system and the tiny spermatozoa lacking a visible flagellum, suggest they belong to a new genus, possibly in the family Macrodasyidae. These hypotheses are supported by the phylogenetic relationships of 47 taxa inferred from analyses of the 18S rRNA gene, which found the new species clustering with Thaidasys tongiorgii in a subset of a larger clade containing Macrodasys. Accordingly, the establishment of the following taxa is proposed: Kryptodasys gen. nov., K. marcocurinii sp. nov., K. carlosrochai sp. nov. and K. ulfjondeliusi sp. nov.

Erratum: Author Correction: Biodiversity estimates and ecological interpretations of meiofaunal communities are biased by the taxonomic approach.

[This corrects the article DOI: 10.1038/s42003-018-0119-2.].

Biodiversity estimates and ecological interpretations of meiofaunal communities are biased by the taxonomic approach.

Accurate assessments of biodiversity are crucial to advising ecosystem-monitoring programs and understanding ecosystem function. Nevertheless, a standard operating procedure to assess biodiversity accurately and consistently has not been established. This is especially true for meiofauna, a diverse community (>20 phyla) of small benthic invertebrates that have fundamental ecological roles. Recent studies show that metabarcoding is a cost-effective and time-effective method to estimate meiofauna biodiversity, in contrast to morphological-based taxonomy. Here, we compare biodiversity assessments of a diverse meiofaunal community derived by applying multiple taxonomic methods based on comparative morphology, molecular phylogenetic analysis, DNA barcoding of individual specimens, and metabarcoding of environmental DNA. We show that biodiversity estimates are strongly biased across taxonomic methods and phyla. Such biases affect understanding of community structures and ecological interpretations. This study supports the urgency of improving aspects of environmental high-throughput sequencing and the value of taxonomists in correctly understanding biodiversity estimates.

A new species of Cephalodasys (Gastrotricha, Macrodasyida) from the Caribbean Sea with a determination key to species of the genus.

A new marine gastrotrich species of the genus Cephalodasys is described from shallow sublittoral coralline sand sampled between Lee Stocking Island and Norman's Pond Cay (Exuma Cays), Bahamas. Cephalodasys interinsularis n. sp. reaches a body length of 471 µm and is characterized by a new combination of characters including six total anterior adhesive tubes and five pairs of ventrolateral adhesive tubes. The new species is morphologically similar to C. swedmarki but can be distinguished by the different number of anterior adhesive tubes, the spatial arrangement of the ventrolateral adhesive tubes, and a shorter pharynx. We provide an updated diagnosis of the genus and a determination key to all known species of Cephalodasys. C. interinsularis n. sp. is the third known species of Cephalodasys from the Caribbean marine province.

Capture of Prey, Feeding, and Functional Anatomy of the Jaws in Velvet Worms (Onychophora).

Onychophorans are carnivorous, terrestrial invertebrates that occur in tropical and temperate forests of the Southern Hemisphere and around the Equator. Together with tardigrades, onychophorans are regarded as one of the closest relatives of arthropods. One of the most peculiar features of onychophorans is their hunting and feeding behavior. These animals secrete a sticky slime, which is ejected via a pair of slime-papillae, to entangle the prey. After the prey has been immobilized, its cuticle is punctured using a pair of jaws located within the mouth. These jaws constitute internalized appendages of the second body segment and are innervated by the deutocerebrum; thus, they are homologous to the chelicerae of chelicerates, and to the (first) antennae of myriapods, crustaceans, and insects. The jaws are also serial homologs of the paired claws associated with each walking limb of the trunk. The structure of the jaws is similar in representatives of the two major onychophoran subgroups, the Peripatidae and Peripatopsidae. Each jaw is characterized by an outer and an inner blade; while the outer blade consists only of a large principal tooth and up to three accessory teeth, the inner blade bears numerous additional denticles. These denticles are separated from the remaining part of the inner jaw by a diastema and a soft membrane only in peripatids. The onychophoran jaws are associated with large apodemes and specialized muscles that enable their movement. In contrast to the mandibles of arthropods, the onychophoran jaws are moved along, rather than perpendicular to, the main axis of the body. Our elemental analysis reveals an increased incorporation of calcium at the tip of each blade, which might provide rigidity, whereas there is no evidence for incorporation of metal or prominent mineralization. Stability of the jaw might be further facilitated by the cone-in-cone organization of its cuticle, as each blade consists of several stacked, cuticular elements. In this work, we summarize current knowledge on the jaws of onychophorans, which are a characteristic feature of these animals.

Soft Bodies, Hard Jaws: An Introduction to the Symposium, with Rotifers as Models of Jaw Diversity.

Jaws have evolved numerous times in the animal kingdom and they display a wide variety of structural, compositional, and functional characteristics that reflect their polyphyletic origins. Among soft-bodied invertebrates, jaws are known from annelids, chaetognaths, flatworms, gnathostomulids, micrognathozoans, mollusks, rotifers, and several ecdysozoans. Depending on the taxon, jaws may function in the capture of prey (e.g., chaetognaths and flatworms), processing of prey (e.g., gnathostomulids and onychophorans), or both (e.g., rotifers). Although structural diversity among invertebrates' jaws is becoming better characterized with the use of electron microscopy, many details remain poorly described, including neuromuscular control, elemental composition, and physical characteristics, such as hardness and resistance to wear. Unfortunately, absence of relevant data has impeded understanding of their functional diversity and evolutionary origins. With this symposium, we bring together researchers of disparately jawed taxa to draw structural and mechanistic comparisons among species to determine their commonalities. Additionally, we show that rotifers' jaws, which are perhaps the best-characterized jaws among invertebrates, are still enigmatic with regard to their origins and mechanics. Nevertheless, technologies such as energy dispersive X-ray spectroscopy (EDX) and 3D modeling are being used to characterize their chemical composition and to develop physical models that allow exploration of their mechanical properties, respectively. We predict that these methods can also be used to develop biomimetic and bioinspired constructs based on the full range of the complexity of jaws, and that such constructs also can be developed from other invertebrate taxa. These approaches may also shed light on common developmental and physiological processes that facilitate the evolution of invertebrates' jaws.

Untangling the Ecology, Taxonomy, and Evolution of Chaetogaster limnaei (Oligochaeta: Naididae) Species Complex.

Within Oligochaeta, Chaetogaster limnaei is unusual in exhibiting a parasitic relationship with freshwater pulmonate snails. Taxonomic confusion has been caused by differences in what have been considered 2 subspecies of this worm: Chaetogaster limnaei limnaei is an ectosymbiont and is present inside the mantle cavity of the snail, whereas Chaetogaster limnaei vaghini is parasitic and lives in the kidney of the snail. This study explored the distribution of these annelids in central New York and used mitochondrial DNA sequence data from the COI locus to examine the relationship, evolution, and species status of the ectosymbiotic and parasitic forms of C. limnaei. Snails ( Physa gyrina ) were collected from 6 streams and lakes in central New York, with additional specimens collected from a lake in Massachusetts for comparison. One hundred and forty snails were examined, and at least 1 form of Chaetogaster was present in 88 specimens, a prevalence of 62.9%. COI sequence data from New York and Massachusetts did not reveal separate ectosymbiotic and parasitic lineages. Instead, all parasitic forms were part of a mixed clade that included both ectosymbiotic and parasitic forms. This mixed clade was nested within clades of ectosymbiotic forms only, suggesting that a plastic lineage of C. limnaei, able to be both ectosymbionts and parasites, evolved from ectoparasitic ancestors.

A new tardigrade, Mutaparadoxipus duodigifinis gen. nov., sp. nov. (Heterotardigrada: Arthrotardigrada), from the Southeastern United States.

A new genus and species of Arthrotardigrada is described from Florida, USA based on its unique adhesive pad/claw combinations. Mutaparadoxipus duodigifinis gen. nov., sp. nov., is characterized by well-developed, ventral secondary clavae that are adjacent to the mouth, pointed lateral and caudal alae, seminal receptacles with coiled ducts opening lateral to the gonopore, and all legs with digits bearing proximal adhesive pads. Distal claws are present on digits I-III of legs I-III, but are missing from digit IV. On leg IV, distal claws are present only on digits II & III. A single accessory point is present on claws II & III only. This is the fourth species discovered to date with proximal adhesive pads, increasing support for a clade of adhesive-padded arthrotardigrades, and is likely the sister taxon of Paradoxipus orzeliscoides. The incomplete set of claws may represent an evolutionary step in a progressive loss of claws hypothesized to have occurred within the Halechiniscidae. The subfamily Orzeliscinae is amended as a result.

A new species of sublittoral marine gastrotrich, Lepidodasys ligni sp. n. (Macrodasyida, Lepidodasyidae), from the Atlantic coast of Florida.

A new species of Lepidodasys is described from sublittoral sandy sediments off the Atlantic coast of Florida. Lepidodasys ligni sp. n. is a small species (≤ 450 µm) with a crossed-helical pattern of small, non-keeled, non-imbricated scales on the dorsal and lateral body surfaces, two columns of ventral, interciliary scales that form a herringbone pattern, and a series of anterior, lateral, dorsal and posterior adhesive tubes. Similar to Lepidodasys castoroides from the Faroe Islands, the new species possesses a caudal constriction that demarcates the posterior end containing the caudal organ. The frontal organ lies within the posterior constriction, which is heavily invested with somatic circular muscles. These muscles are also present throughout the trunk and represent a novel condition for species of Lepidodasys,which were previously considered to lack somatic circular muscles. Posterior of the caudal constriction is a large, barrel-shaped caudal organ that is wrapped in a series of interdigitating, spindle-shaped, incomplete circular muscle fibers. The caudal organ contains a sclerotized central canal, but the absence of distal cuticular endpieces distinguishes the new species from its morphologically similar congener, Lepidodasys castoroides.

Acanthodasys paurocactus sp. n., a new species of Thaumastodermatidae (Gastrotricha, Macrodasyida) with multiple scale types from Capron Shoal, Florida.

A new species of Acanthodasys (Gastrotricha, Macrodasyida, Thaumastodermatidae) is described from sublittoral sediments off the Atlantic coast of Florida. Acanthodasys paurocactussp. n. is a relatively small species (to 450 µm long) with a strap-shaped outline, a series of anterior, lateral, and ventrolateral adhesive tubes, paired caudal pedicles with posterior adhesive tubes, and a morphologically diverse cuticle. The cuticle contains both spined and unspined scales. Unspined scales are present in two general shapes: lanceolate and eye shaped, with some transitional shapes. All scales have a thickened rim and depressed central region; some scales of both shapes bear either one or more central bumps, a parallel ridge, or a perpendicular ridge that gives the appearance of a cross-shaped pattern under transmitted light. Spined scales are somewhat quadrangular in shape and bear uniancres to 15 µm long with a cross-shaped sectional profile. The new species is now one of five described species to possess both spined and spineless scales, and only one of two species to possess two types of spineless scales (the second species is an incompletely described specimen from Norway).

Gastrotricha: a marine sister for a freshwater puzzle.

BACKGROUND: Within an evolutionary framework of Gastrotricha Marinellina flagellata and Redudasys fornerise bear special interest, as they are the only Macrodasyida that inhabit freshwater ecosystems. Notwithstanding, these rare animals are poorly known; found only once (Austria and Brazil), they are currently systematised as incertae sedis. Here we report on the rediscovery of Redudasys fornerise, provide an account on morphological novelties and present a hypothesis on its phylogenetic relationship based on molecular data. METHODOLOGY/PRINCIPAL FINDINGS: Specimens were surveyed using DIC microscopy and SEM, and used to obtain the 18 S rRNA gene sequence; molecular data was analyzed cladistically in conjunction with data from 42 additional species belonging to the near complete Macrodasyida taxonomic spectrum. Morphological analysis, while providing new information on taxonomically relevant traits (adhesive tubes, protonephridia and sensorial bristles), failed to detect elements of the male system, thus stressing the parthenogenetic nature of the Brazilian species. Phylogenetic analysis, carried out with ML, MP and Bayesian approaches, yielded topologies with strong nodal support and highly congruent with each other. Among the supported groups is the previously undocumented clade showing the alliance between Redudasys fornerise and Dactylopodola agadasys; other strongly sustained clades include the densely sampled families Thaumastodermatidae and Turbanellidae and most genera. CONCLUSIONS/SIGNIFICANCE: A reconsideration of the morphological traits of Dactylopodola agadasys in light of the new information on Redudasys fornerise makes the alliance between these two taxa very likely. As a result, we create Anandrodasys gen. nov. to contain members of the previously described D. agadasys and erect Redudasyidae fam. nov. to reflect this novel relationship between Anandrodasys and Redudasys. From an ecological perspective, the derived position of Redudasys, which is deeply nested within the Macrodasyida clade, unequivocally demonstrates that invasion of freshwater by gastrotrichs has taken place at least twice, in contrast with the single event hypothesis recently put forward.

Acanthodasys caribbeanensis sp. n., a new species of Thaumastodermatidae (Gastrotricha, Macrodasyida) from Belize and Panama.

We describe one new species of Acanthodasys (Gastrotricha, Macrodasyida, Thaumastodermatidae) collected from sublittoral sites around Carrie Bow Cay, Belize and Isla Colón in the Bocas del Toro archipelago, Panama. Though eight species of Acanthodasys are currently recognized, no species has yet been reported from the Caribbean. Acanthodasys caribbeanensissp. n. is characterized by the lack of lateral adhesive tubes, the presence of ventrolateral adhesive tubes, and with cuticular armature in the form of both spineless and spined scales. The spineless scales are not elliptical as in other species of Acanthodasys, but are instead variable in shape and closely resemble the spineless scales of species of Diplodasys. Spined scales bear uniancres up to 50 µm long and are the largest reported in the genus. Uniancres are arranged dorsally around the mouth rim and distributed in five distinguishable columns. Adult size varies from 325-625 µm long.

Three-dimensional reconstruction and neural map of the serotonergic brain of Asplanchna brightwellii (Rotifera, Monogononta).

The basic organization of the rotifer brain has been known for nearly a century; yet, fine details on its structure and organization remain limited despite the importance of rotifers in studies of evolution and population biology. To gain insight into the structure of the rotifer brain, and provide a foundation for future neurophysiologic and neurophylogenetic research, the brain of Asplanchna brightwellii was studied with immunohistochemistry, confocal laser scanning microscopy, and computer modeling. A three-dimensional map of serotonergic connections reveals a complex network of approximately 28 mostly unipolar, cerebral perikarya and associated neurites. Cells and their projections display symmetry in quantity, size, connections, and pathways between cerebral hemispheres within and among individuals. Most immunopositive cells are distributed close to the brain midline. Three pairs of neurites form decussations at the brain midline and may innervate sensory receptors in the corona. A single neuronal pathway appears to connect both the lateral horns and dorsolateral apical receptors, suggesting that convergence of synaptic connections may be common in the afferent sensory systems of rotifers. Results show that the neural map of A. brightwellii is much more intricate than that of other monogonont rotifers; nevertheless, the consistency in neural circuits provides opportunities to identify homologous neurons, distinguish functional regions based on neurotransmitter phenotype, and explore new avenues of neurophylogeny in Rotifera.