Reconstrucción tridimensional de la musculatura F-actina de Dorvillea kastjani (Dorvilleidae: Polychaeta) por medio de marcado con phalloidina y cLSM

This paper is part of a series investigating the muscular architecture of various “Polychaeta”, aiming to ascertain the presence of circular muscles in the body wall, which have recently been thought to be lacking more often than hitherto known. The F-actin muscular subset of Dorvillea kastjani was labelled with phalloidin and the architecture three-dimensionally reconstructed by means of confocal laser scanning microscopy. Three pairs of longitudinal, two transverse and numerous radial muscles ensure shape and flexibility of the prostomium. Mobility of the sub-biramous parapodia and their chaetae is achieved by seven different muscle types. The body wall contains transverse and bracing muscles and in total five longitudinal muscle strands: two dorsolateral, two ventral and one ventromedial. Numerous transverse fibres extend from the dorsal side peripherally and ventrally and become concentrated into six or seven pairs of bundles per segment on the ventral side. They terminate before reaching the midline, leaving a gap of only a few micrometres between them. Within the intersegmental furrows these fibres form complete rings in a supralongitudinal postion. Thus, true circular fibres exist in D. kastjani but are weakly developed.Este trabajo forma parte de una serie de trabajos que investigan la arquitectura muscular de diferentes especies de Poliquetos con el objetivo de comprobar la presencia de musculatura circular en su cuerpo; recientemente se piensa que dicha musculatura podría estar ausente más a menudo de lo hasta ahora pensado. La musculatura F-actina de Dorvillea kastjani fue marcada con phalloidina y su arquitectura reconstruida tridimensionalmente por medio de microscopia de scanning laser confocal. Tres pares longitudinales, dos tranversales y numerosos músculos radiales aseguran la flexibilidad y la forma del prostómio. La mobilidad de los parápodos sub-biramios y sus quetas se obtiene gracias a siete diferentes tipos de músculos. La cavidad del cuerpo contiene musculos tranversales y diagonales y en total cinco ramas de músculos longitudinales: dos dorsolaterales, dos ventrales y una medioventral. Numerosas fibras transversales se extienden desde la zona dorsal periféricamente y centralmente y se concentran en seis o siete pares de paquetes por segmento en la cara ventral. Estos terminan antes de alcanzar la línea central dejando un vacio de unas micras entre ellos. Entre los surcos entre segmentos, las fibras forman anillos completos en una posición supralongitudinal. Además, verdaderas fibras circulares existen en Dorvillea kastjani pero están débilmente desarrolladas. &nbsp

The central nervous system of Oweniidae (Annelida) and its implications for the structure of the ancestral annelid brain

Figure S1: Histology Orrhage’s Owenia fusiformis. A: slide showing sections of Owenia fusiformis. B: Intermediate filaments (if) cross the neuropil of the brain (br). The ecm of the epidermis is less prominent where the neuropil layer is above it. C: Posterior part of the brain (br). if: intermediate filaments. (JPG 10649 kb

Invertebrate neurophylogeny: suggested terms and definitions for a neuroanatomical glossary

<p>Abstract</p> <p>Background</p> <p>Invertebrate nervous systems are highly disparate between different taxa. This is reflected in the terminology used to describe them, which is very rich and often confusing. Even very general terms such as 'brain', 'nerve', and 'eye' have been used in various ways in the different animal groups, but no consensus on the exact meaning exists. This impedes our understanding of the architecture of the invertebrate nervous system in general and of evolutionary transformations of nervous system characters between different taxa.</p> <p>Results</p> <p>We provide a glossary of invertebrate neuroanatomical terms with a precise and consistent terminology, taxon-independent and free of homology assumptions. This terminology is intended to form a basis for new morphological descriptions. A total of 47 terms are defined. Each entry consists of a definition, discouraged terms, and a background/comment section.</p> <p>Conclusions</p> <p>The use of our revised neuroanatomical terminology in any new descriptions of the anatomy of invertebrate nervous systems will improve the comparability of this organ system and its substructures between the various taxa, and finally even lead to better and more robust homology hypotheses.</p

Ultrastructure and functional morphology of the appendages in the reef-building sedentary polychaete Sabellaria alveolata (Annelida, Sedentaria, Sabellida)

Background: The sedentary polychaete Sabellaria alveolata, the sandcastle or honeycomb worm, possesses four different kinds of appendages besides the parapodia: opercular papillae, tentacular filaments, palps, and branchiae. It exhibits a highly specialized anterior end, the operculum, formed by the prostomium, peristomium, and two anterior segments. The operculum comprises opercular papillae, tentacular filaments, and palps. Paired branchiae are present from the second thoracic chaetiger onwards on the posteriorly following segments except for the last ones. Ultrastructural data on these appendages are either scanty, incomplete, or even lacking in Sabellariidae. In order to analyze their functional morphology, to bridge the data gap, and providing data for future phylogenetic and evolutionary analyses, we investigated the appendages of S. alveolata by applying light microscopy, confocal laser scanning microscopy, scanning, and transmission electron microscopy. Results: In S. alveolata the entire body is covered by a thin cuticle characterized by the absence of layers of parallel collagen fibers with no differentiation between the various body regions including the branchiae. The opercular papillae bear numerous tufts of receptor cells and lack motile cilia. The tentacular filaments show a distinctive pattern of motile cilia. Their most conspicuous morphological feature is a cell-free cartilaginous endoskeletal structure enclosed by ECM. Besides musculature the filaments include a single coelomic cavity but blood vessels are absent. The palps are ciliated and possess two coelomic cavities and a single blind-ending internal blood vessel. Besides external ciliation and receptor cells, the coelomate branchiae are highly vascularized and equipped with numerous blood spaces extending deep between the epidermal cells resulting in low diffusion distances. Conclusions: All appendages, including the branchiae, bear receptor cells and, as such, are sensory. The opercular papillae resemble typical parapodial cirri. In contrast, the tentacular filaments have a triple function: sensing, collecting and transporting particles. A similarity to branchiae can be excluded. The palps are typical grooved palps. A revised classification of polychaete branchiae is suggested; thereby, the branchiae of S. alveolata belong to the most common type comprising coelom, musculature, and blood vessels. The results indicate that diffusion distances between blood and environment have been underestimated in many cases

Marine connectivity dynamics: clarifying cosmopolitan distributions of marine interstitial invertebrates and the meiofauna paradox

Many interstitial species were first described as widely distributed, often cosmopolitan or amphi-oceanic, contrasting with descriptions of a sedentary life style and the general absence of pelagic dispersal stages. These inconsistencies became known as the “meiofauna paradox”. In this review, we present a literature review investigating these inconsistencies and address the assumptions of the meiofauna paradox. We break the paradox down to two aspects including species distribution and dispersal. Focusing on distribution, we demonstrate that wide distributions are seldom given and false records likely stem from biological phenomena like stasis or recent speciation. These phenomena account for morphological similarity, ultimately represented by the pronounced occurrence of cryptic species with restricted distribution ranges. Additionally, taxonomic artefacts such as the erroneous application of taxonomic keys contribute to the report of widely distributed species. Considering dispersal, we point out the mismatch between traditional assumptions of meiofaunal sedentarism and growing experimental and empirical evidences suggesting higher dispersal potential. These evidences include not only indications for dispersal by pelagic stages, but further consider ecological and life-history traits in shaping distribution ranges. We conclude that the meiofauna paradox sensu stricto most likely does not exist and provide a roadmap for future research, suggesting a focus on morphological similarity and marine connectivity. Meiofaunal research should concentrate on evolutionary factors resulting in morphological similarity, improving the taxonomic resolution of species complexes and conducting more sophisticated experimental experiments to meiofaunal dispersal. In all cases, meiofaunal research will benefit from high-throughput sequencing such as genome scanning approaches, metagenomics or metatranscriptomics