Alexander Kieneke

Molecular surveys and studies of the muscle anatomy made evident that the mesopsammic gastrotrich Xenotrichula intermedia, previously regarded as a cosmopolitan species, comprises several distinct taxonomic units. These entities are to date referred to as cryptic species. Although other morphological traits seemed insufficient to differentiate geographically distant populations, investigations of the myomorphology displayed significant differences. Three muscular morphotypes of X. intermedia are known and distinguishable via properties of their dorsoventral and circular musculature. However, previous studies using confocal laser scanning microscopy (CLSM) conducted observations of the muscle architecture that aimed to apply older terminology of the only existing reconstruction that was based on fluorescence microscopy. Since detailed 3D reconstructions of the myoanatomy were never performed, comparisons between different morphotypes of X. intermedia stay a difficult endeavor. In this study, the muscular system of a North Sea population of X. intermedia is investigated and reconstructed using CLSM and 3D reconstruction software. Our aim is to test whether this population, adjacent to the type locality of X. intermedia, constitutes another muscular morphotype. The overall musculature of the North-Sea population is similar to that of the Mediterranean specimens. A Baltic Sea individual appears myoanatomically identical to these populations, too. This indicates a distinct morphotype with a pan-European distribution. Since the known muscular morphotypes are clearly distinguishable, we propose the presence of a species complex comprising a pan-European X. intermedia, a Persian X. aff. intermedia and a NW Atlantic X. aff. intermedia. Furthermore, our investigation demonstrates a much higher complexity of the longitudinal musculature than previously assumed, which leads us to reinterpret earlier myomorphological data, amend some terminology, and reconsider statements of homology that will provide a feasible foundation for future comparative studies.

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

Species of the marine meiofauna such as Gastrotricha are known to lack dispersal stages and are thus assumed to have low dispersal ability and low levels of gene flow between populations. Yet, most species are widely distributed, and this creates a paradox. To shed light on this apparent paradox, we test (i) whether such wide distribution may be due to misidentification and lumping of cryptic species with restricted distributions and (ii) whether spatial structures exist for the phylogeography of gastrotrichs. As a model, we used the genus Turbanella in NW Europe. DNA taxonomy using a mitochondrial and a nuclear marker supports distinctness of four traditional species (Turbanella ambronensis, T. bocqueti, T. mustela and T. cornuta) and provides evidence for two cryptic species within T. hyalina. An effect of geography on the within‐species genetic structure is indeed present, with the potential for understanding colonization processes and for performing phylogeographic inference from microscopic animals. On the other hand, the occurrence of widely distributed haplotypes indicates long‐distance dispersal as well, despite the assumed low dispersal ability of gastrotrichs.

Kieneke, A. and Hochberg, R. 2012. Ultrastructural observations of the protonephridia of Polymerurus nodicaudus (Gastrotricha: Paucitubulatina). —Acta Zoologica (Stockholm) 93: 115–124.We studied different regions of the protonephridia of the limnic gastrotrich Polymerurus nodicaudus by means of light and electron microscopy to determine how freshwater species might differ from their marine relatives. Microscopic and ultrastructural characters are in accordance with another limnic species of Paucitubulatina, Chaetonotus maximus, whose protonephridial system has been previously reconstructed. Shared protonephridial characters of both species include the presence of highly elongate terminal organ cilia, microvilli, and the canal cell lumen as well as the presence of a conspicuous anterior loop of the protonephridial lumen. These features are not present in representatives of earlier, marine, paucitubulatan lineages (i.e., Xenotrichulidae) and so are assessed as evolutionary novelties that were likely important for the successful colonization of the freshwater environment.

A new species of the marine gastrotrich taxonThaumastodermais described. A single specimen of this species,Thaumastoderma antarcticasp. nov., was extracted from silty sediment sampled at one station of the Andeep-1 cruise, about 150 km to the north of the South Shetland Islands (Drake Passage, South Atlantic Ocean). This paper provides the first record of this genus from the deep sea and the second description of a macrodasyid gastrotrich living in an abyssal habitat. The new species is characterized by several apomorphic features, among them a caudal pair of strongly elongated dorsal cirrata tubes. A phylogenetic analysis of the genusThaumastodermareveals thatTh. antarcticais closely related toTh. coronariumandTh. appendiculatum. Furthermore, the analysis offers an evolutionary scenario and a hypothesis for the internal phylogeny of this taxon while supporting its monophyly. It is the first time a cladistic analysis has been conducted for a delimited group of gastrotrichs, i.e. for all known members of a genus.