ABSTRACT Micro-computed tomography is a non-invasive technique that allows 3D rendered images with anatomical information, which facilitates functional anatomy interpretations. Its usefulness has already been proven in several animal groups of relatively small size, but it has rarely been applied for the anatomical and morphological investigation of meiofaunal organisms. Here, we tested micro-CT as a potential technique for anatomical studies on Kinorhyncha, a hard-bodied meiofauna phylum. The morphological information obtained from our micro-CT images regarding the cuticle, epidermis, digestive, excretory, and reproductive systems fits with the known anatomical information on kinorhynchs through classical techniques such as Light Microscopy (LM), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM), thus presenting a valid option when few specimens are available for study, as it is practically a non-invasive technique for the morphological study of these animals.

AimBiogeography and macroecology aim to understand the processes that determine patterns in nature. In the marine environment, most of what we know has been documented for fish and macrobenthic organisms. As a result, this knowledge is negatively biased towards smaller benthic organisms, including meiofauna. In this study, we analysed the occurrence of species from the phylum Kinorhyncha, a meiobenthic group with presumably low dispersal potential.LocationAround the Iberian Peninsula. Our goal was to explore the biogeographic and macroecological patterns across the Lusitanian and Mediterranean Sea biogeographic provinces.Time Period1990-2021.Major Taxa StudiedKinorhyncha Reinhard 1885.MethodsSpecies occurrence data were examined in relation to marine biogeographical classifications, considering multiple spatial scales across the Iberian Peninsula and key environmental variables. We applied generalised linear models (GLMs), generalised additive models (GAMs), and permutational multivariate analysis of variance (PERMANOVA) to evaluate the influence of province, ecoregion, area, sediment type, depth, latitude, and longitude on Kinorhyncha species richness and composition.ResultsSpecies richness was primarily influenced by depth and biogeographic province, while species composition was better explained by area (geographic location) and sediment type. These results indicate that geographic location is a significant factor influencing the composition and distribution of Kinorhyncha. Despite their low dispersal capacity and limited mobility, we found that both provinces shared species. The Mediterranean Sea contained more exclusive species, despite being less thoroughly sampled.Main ConclusionsWe found a biogeographic affinity between Atlantic and Mediterranean kinorhynchs, suggesting their coexistence across both marine provinces. However, species associations were weak at this broader spatial scale, underscoring the need to investigate finer-scale patterns, such as areas within specific regions, to more accurately characterise meiofaunal distribution. While this study focused exclusively on Kinorhyncha, we anticipate that similar spatial patterns may be present in other meiofaunal taxa lacking planktonic larvae, given their inherently limited dispersal capabilities.

A new species of the cyclorhagid genus Meristoderes is described. Meristoderes zmaj sp. n. is distinguished from its congeners by its unique arrangement of spines and tubes. It possesses acicular spines on segments 4, 6 and 8 in middorsal position and on segments 6-9 in lateroventral position; and tubes on segment 2 in subdorsal, midlateral and ventrolateral position, on segment 5 in lateroventral position and on segment 10 in laterodorsal position. With the formal description of M. zmaj sp. n., the number of species within the genus is increased to 10. In addition, the appearance of a new species and its accompanying fauna within the North-Eastern Adriatic Sea fauna, extensively studied by Kinorhyncha taxonomists, is discussed.

Nematodes typically comprise the most abundant phylum in meiofaunal communities. We aim to characterize the specific ecological conditions that influence Nematoda communities in Posidonia oceanica grasslands focusing on three habitats: leaves, matte, and unvegetated adjacent sediment. We hypothesized that the constant flux of nutrients under the canopy would result in a higher concentration of metazoans compared to the unvegetated sediment outside; however, the hypothesis was not confirmed by the obtained results. The habitat heterogeneity played an important role in shaping the community, yielding a greater richness in the matte. The resource specificity of the leaves (microepiphytes) was also expected to shape the community by favoring nematodes capable of exploiting this resource (epistratum feeders with scraping-like structures), such as the family Chromadoridae that dominated this habitat. In addition, the high light exposure of the leaves explains the higher concentration of ocellated nematodes in this habitat. Organic carbon and nitrogen contents had an impact on the Nematoda community composition, meanwhile average grain size only affected the abundance of nematodes with elongated/filiform tails.

The coining of new species names is one of the most creative processes in science. Scientific names must be unique and stable over time to allow researchers to communicate knowledge on species unambiguously worldwide. Despite the importance of biological nomenclature, few studies analyze nomenclatural trends, which can offer interesting information. In the present paper, we explore different trends in naming Kinorhyncha species over time to answer questions related to kinorhynch nomenclatural acts, compare trends among the different specialists and discuss possible suggestions for future species discoveries. We focus on detecting the main practices followed by the phylum specialists when coining new specific names, temporal trends in the used language and etymological basis for creating the names and differences between author preferences. It is interesting that not all Kinorhyncha names correspond to valid species, although the proportion of not accepted and uncertain names is low. On the other hand, the usage of classical languages (Latin and Greek) remains temporarily stable when coining species names, but other modern languages such as English, Spanish, Danish and Japanese are on the rise, partly due to the nationality of the current kinorhynchologists. Regarding the etymological basis, a replacement of traditional categories (morphology, geography) by eponyms has not been detected, even though the usage of the latter has significantly increased in recent years. Finally, since the creation of names is undoubtedly subjective, personal trends among the authors are obvious, each one following their own style and preferences.

The scientific life of Robert P. Higgins was devoted to meiofauna, microscopically small animals living in aquatic sediments from the intertidal to hadal depths worldwide. He focused on the taxonomy, life-history, and ecology of the marine taxa Kinorhyncha, Tardigrada, and Priapulida and co-discovered the phylum Loricifera. He improved the methods for studying meiofauna and contributed significantly to spreading knowledge about these animals. Aspects of his life are described and lists of his publications, taxa described, contributions to science, and honours received are provided.

AimThe interplay between distribution ranges, species traits and sampling and taxonomic biases remains elusive amongst microscopic animals. This ignorance obscures our understanding of the diversity patterns of a major component of biodiversity. Here, we used marine Halacaridae to explore whether differences between marine provinces can explain their distribution patterns or if differential sampling efforts across regions prevent any macroecological inference. Furthermore, we test if certain functional traits influence their distribution patterns. LocationEurope. ResultsWhereas geographical variables provided a better explanation for differences in species composition, sampling effort and distance from marine biological stations accounted for the majority of differences in European Halacaridae richness. Species occurring in more habitats showed broader geographical ranges and accumulated more records. Species traits like generalism affected the distribution of halacarid species. Main ConclusionsWe propose that the sampling effort of halacarid mites in Europe might be explained by two different cognitive biases: the convenience of selecting certain sampling localities compared to others and the tendency of zoologists to scrutinise habitats where their target organisms are more common.

Six of the eight species of the genus Setaphyes have been described from Europe. In the present contribution, the European Setaphyes species are revised and two of them, S. dentatus (Reinhard, 1881) and S. kielensis (Zelinka, 1928), are redescribed following the current approaches of Kinorhyncha taxonomy. For this purpose, material from 17 localities throughout the Atlantic Ocean and the Mediterranean and Black Seas was investigated. The redescriptions of two of the most common pycnophyid species in Europe include detailed information on intraspecific variation among populations. Setaphyes dentatus is characterized by the presence of middorsal elevations on segments 2–6, and middorsal processes on segments 1, 7–9, unpaired paradorsal setae on segments 2–9; laterodorsal setae on segments 3, 5 and 7; ventromedial setae on segments 4–5, 7–8 in males and 3–5, 7–9 in females; anterior cuticular, reticulate ridges on the tergal plate of segment 1 and conspicuous patch of laterodorsal and ventrolateral longitudinal, cuticular ridges on segment 10. Setaphyes kielensis is characterized by middorsal elevations on segments 1–9; paired paradorsal setae on segments 2–9 (unpaired on segment 8); laterodorsal setae on segments 2–9; ventromedial setae on segments 3–9. Furthermore, morphometric features of the European Setaphyes are analysed. Specifically, the morphometric analyses revealed sex-specific variability in the LTS/TL proportion, with females of all the European species of Setaphyes showing smaller LTS/TL. Thus, the LTS/TL ratio unveils a conspicuous sexual dimorphism in the genus.

Taxonomic studies of the phylum Kinorhyncha follow a standardised structure, which is extremely useful in many aspects, such as making it easier to read and compare the different species descriptions. Nevertheless, the morphological measurements methods, essential for formal description of species, may differ according to the authors. In the present contribution, we propose a standardised method of taking and representing the measurements, with the aim of obtaining comparable and repeatable morphometric results. Additionally, we propose an online repository to make the measurements accessible to all researchers in the same format, facilitating future comparisons and studies. Finally, a glossary that compiles and defines all the measurements that may be included in Kinorhyncha descriptions is presented.

Polymetallic nodule fields represent a large reservoir of undiscovered biodiversity that becomes particularly evident for meiobenthic organisms, the smallest-sized faunal group. Knowledge gaps are especially noticeable for the generally low-density metazoan groups, such as Kinorhyncha, the so-called mud dragons. Using both morphological and genetic (metabarcoding) approaches, we provide a general overview and comparison of the diversity of kinorhynchs collected during nine sampling campaigns (2016–2019) that targeted abyssal environments in several contract areas for exploration in the Clarion-Clipperton Fracture Zone (CCZ) and in the Peru Basin. Our findings from morphological analyses reveal a highly diverse mud dragon community, with 16 species present in the CCZ. Of these, 12 appear in the German contract area, including three new species described in the present contribution: Echinoderes delaordeni sp. nov., Echinoderes sanctorum sp. nov., and Echinoderes zeppilliae sp. nov. Furthermore, metabarcoding data of the kinorhynch community gathered from the area is provided, together with the geographic distribution of the known species stated per contractor area, including new records and still undescribed species. Most of the identified species in the CCZ seem to have a wide distribution, with Echinoderes sp.4 being the most common and abundant species with a distribution spreading across the CCZ and also present in the Peru Basin. Metabarcoding analyses targeting the V1V2 hypervariable region of the 18S gene from the 253 stations of the CCZ revealed 14 amplicon sequence variants (ASVs) belonging to Kinorhyncha with grade values higher than 98% detected at 15 different stations within six different areas along the CCZ. Concurring with morphology, the family Echinoderidae was the most diverse as the genus Cephalorhyncha had five ASVs, followed by Echinoderes with four ASVs. Semnoderes , however, showed the widest spread ASV, being detected at six stations. In the CCZ, the metabarcoding data showed there were no shared ASVs between the CCZ areas as well as the highest number of uniques, which was 11. Our morphological study showed a low number of specimens inhabiting nodules (surface/crevices), suggesting that specific kinorhynch species do not typically inhabit the nodules in addition to the surrounding sediment.

The kinorhynch fauna from Portugal has been explored, yielding a new species of the genus Setaphyes (Kinorhyncha: Allomalorhagida). This is the first description of an allomalorhagid species from Portugal. Specimens of the new species were collected at a subtidal muddy beach in Alvor, a village located in the southernmost region of Portugal. Setaphyes algarvensis sp. nov. may be distinguished from its congeners by a unique arrangement of the setae: paired paradorsal setae on segments 2–7 and 9, paradorsal seta on segment 8 unpaired, laterodorsal setae on segments 2–3 and 6–9 in males and 2–9 in females, paralateral setae on segment 1, lateroventral setae on segments 2–10 (two pairs on segment 5), ventrolateral setae on segment 1 in males and 1–3 in females, and ventromedial setae on segments 3–9 in males and 4–9 in females. The diagnostic features of Setaphyes algarvensis sp. nov. are discussed from a comparative perspective with the congener species. Additionally, morphometric analyses of selected features, namely the total trunk length and the relation between the total trunk length and the length of lateral terminal spines, turned out to be useful to distinguish between the new species and Setaphyes kielensis (its most similar congener).

A new Dracoderidae genus, Dracophyes gen. nov., and a new species Dracophyes cepedai sp. nov. from the Peru Basin are described. The new genus is characterized by the presence of acicular spines showing conspicuous intracuticular structures on segments 1–9 (either anchor for the dorsal or groove-like for the lateral series), alternating laterally displaced dorsal spines, becoming more lateral towards the posterior segments, males with two pairs of minute, poorly sclerotized penile spines, and its conspicuous obovate trunk shape. The new genus accommodates three species: Dracophyes toyoshioae comb. nov., Dracophyes chaac comb. nov. and D. cepedai sp. nov. The latter was collected in abyssal depths in the Peru Basin (East Pacific Ocean) and is recognised by having dorsal acicular spines on segments 1 to 9, alternating laterally displaced from the middorsal line, ventral acicular spines in ventrolateral position on segment 1, lateroventral position on segments 2–4 and 6–9, and in lateral accessory position on segment 5, tubes in lateroventral position on segment 5 and in lateral accessory position on segments 2 and 8, type 2 glandular cell outlets in lateroventral position on segment 10 and extremely long lateral terminal spines. Moreover, with the erection of the new genus, emended diagnoses for the family Dracoderidae and the former single genus within the family, Dracoderes , are proposed.

We present a data set on marine mites (family Halacaridae) in European waters. The data set gathers all the published records of marine mites from the North European Seas, Lusitania, Mediterranean Sea and Black Sea marine provinces, all belonging to the temperate North Atlantic geographical realm. The database includes 3006 records collected from 260 original publications. For each record, the dataset provides complementary taxonomic, geographical, and ecological information, as well as remarks regarding the sampling methods used in each study. We use this dataset to briefly discuss potential knowledge gaps and biases across marine regions and habitats. We hope that these data will provide a baseline for further studies in biogeography and ecology.

La Colección de Invertebrados es una de las 17 colecciones científicas del Museo Nacional de Ciencias Naturales de Madrid (MNCN-CSIC). Hasta la fecha, dicha colección comprendía ejemplares pertenecientes a 27 filos animales. El presente trabajo informa de la donación de 44 ejemplares pertenecientes a 25 especies, 13 géneros y seis familias del filo Kinorhyncha, lo que amplía hasta 28 el número de filos representados en la citada colección. Para cada especie se aportan datos del lugar, fecha y proyecto de procedencia. Además, se reporta por primera vez la especie Pycnophyes giganteus en aguas baleares.

The ecosystem formed by the marine flowering plant Posidonia oceanica is a biodiversity reservoir and provides many ecosystem services in coastal Mediterranean regions. Marine meiofauna is also a major component of that biodiversity, and its study can be useful in addressing both theoretical and applied questions in ecology, evolution, and conservation. We review the meiofaunal diversity in the meadow ecosystem of P. oceanica by combining a literature review and a case study. First, we gathered records of 672 species from 71 published studies, as well as unpublished sources, highlighting 4 species exclusive to this ecosystem. Eighteen of those studies quantified the spatial and temporal changes in species composition, highlighting habitat-specific assemblages that fluctuate following the annual changes experienced by these meadows. Hydrodynamics, habitat complexity, and food availability, all three inherently linked to the seagrass phenology, are recognized in the literature as the main factors shaping the complex distribution patterns of meiofauna in the meadows. These drivers have been identified mainly in studies of Copepoda and Nematoda, and their effect may depend ultimately on species-specific preferences. Second, we tested the generality of these observations using marine mites as a model group, showing that similar ecological preferences might be found in other less abundant meiofaunal groups. Overall, our study highlights the high diversity of meiofauna in meadows of P. oceanica compared with algae and sessile macrofauna associated with this seagrass and shows the complexity of the interactions and habitat use by meiofauna associated with the seagrass.

Kinorhynchs from eight sandy, shallow water localities along the west and south coasts of Turkey were examined. The study resulted in the finding of six different species: Two species, Echinoderes gerardi and Cephalorhyncha flosculosa were known from Turkey, two species, Echinoderes riedli and Campyloderes vanhoeffeni were known from the Mediterranean, but are new to Turkey, and two species, Echinoderes sp. and E. shahmaranae sp. nov. are new to science. Echinoderes sp. resembles E. charlotteae from the Gulf of Mexico, but differs at some minor points. However, since only a single specimen was available, only diagnostic details, but no formal description, is provided. Echinoderes shahmaranae sp. nov. is described from Mugla. The species is distinguished by its unique combination of spine; tube and glandular cell type 2 distributions, as well as the presence of conspicuous, rigid, paraventral cuticular hairs. The latter character was evaluated across all echinoderid species from which information was available. It is present in only sixteen other echinoderid species, and is considered to be a character of potential phylogenetic significance. Other morphological findings include the confirmed lack of paradorsal sensory spots on segments 4 and 5, and presence of a middorsal fissure on segment 11 in C. flosculosa.

Hands-on experience is critical to teaching invertebrate zoology, as students are unfamiliar with many animals and theoretical concepts are sometimes difficult to assimilate. As part of a fully online course, we decided to give students a box of take-home materials so that they could do hands-on work in their homes under the guidance of the teacher or at their own pace following the lecture scripts and presentations. The box contained whole specimens fixed in ethanol for observation and dissection, dried material such as skeletons and shells, and microscope slides. We also included a USB digital microscope to facilitate visualization of details and slides. The experience was very satisfying and proved to be not only a good alternative for mandatory online classes in times of pandemic, but also an interesting resource to supplement face-to-face classes.

Author(s): Garcia Herrero, Alvaro; Martinez, Alejandro; Garcia-Gomez, Guillermo; Sanchez, Nuria; Bird, Graham; Fontaneto, Diego; Pardos, Fernando | Abstract: We describe a dataset on the crustacean Order Tanaidacea from the coasts of the Iberian Peninsula and surrounding seas, including the archipelagos of the Azores, Madeira, Savage, and the Canary Islands. The dataset gathers the records from all available sources published between 1828 to 2019, which were collected following a standardized Google Scholar search and cross checking each article’s reference lists. For each record, the dataset includes taxonomic, geographical, and ecological information, as well as remarks regarding the sampling methods. The dataset was further completed with 52 additional unpublished records obtained from screening the collections of the University Complutense of Madrid gathered from 35 shallow water surveys. Furthermore, 698 records from different oceanographic deep-sea campaigns have also been included. In total, 3456 records from 186 species in 22 families have been compiled. The dataset organises the current published and unpublished knowledge on tanaidaceans in the area and, by making it open access, it will allow comparisons of the distribution of tanaidaceans in zoogeographic studies.n

We are starting to appreciate that microscopic animals are not as widespread as previously thought, but we still ignore to what extent and through which mechanisms the environment selects for specific communities or traits in microscopic animals. We here analyse the functional diversity of marine mite communities living in a seagrass meadow across two habitats: the leaves and the matte. The strictly benthic lifestyle and the conserved morphology of mites allow for unambiguous characterisation of their functional traits, while the discrete nature of the two habitats alleviates the uncertainty in their ecological characterisation. Our results show that habitat filters the distribution of certain traits favouring a higher diversity, dispersion, and evenness of functional traits in the matte than in the leaves. We further observed temporal variations in the functional diversity of communities, following the changes in biomass and structure of seagrass leaves. However, despite the stark differences between the two habitats, the filtering effect is partial and affects mostly relative species abundances. Our study emphasises the need of moving from a taxonomical towards a functional view of ecological studies of microscopic organisms. This integrative approach is key to achieve a mechanistic understanding of their habitat and distribution patterns.

Size-latitude trends in the meiobenthic phylum Kinorhyncha, commonly known as mud dragons, have been explored in oceans worldwide. Generalized least squares regression was used to assess relationships between size and latitude, as well as between size, latitude, and two selected environmental variables that exhibit latitudinal gradation: the sea surface temperature and the net primary productivity. Different structures of spatial autocorrelation and potential confounding factors, such as the species richness and the number of kinorhynch records that could affect latitudinal gradients, were also addressed. In addition, generalized mixed models were used to determine the influence of the phylogeny on body size. Size-latitude relationships of Kinorhyncha were commonly found globally, as well as for particular geographic regions (hemispheres and/or coastlines), with important differences between taxonomic groups. These size-latitude trends were heterogeneous and implied the influence of the latitude itself, environmental variables, and phylogeny. These facts indicate that a single underlying process is not likely to explain the observed relationships but a complex interaction of several macroecological patterns both present and past. Perhaps, the inclusion of future new reports, conducted in undersampled areas, may shed some light on the matter and reveal more generalized size-latitude patterns. Nevertheless, it is also likely that broadly generalizable size-latitude relationships may not exist in meiofaunal communities.