No abstract

The morphology of ctenostome bryozoans remains little investigated with only few species having been subject to more detailed studies. From all the seven main different superfamilies, only few representatives have been studied. The superfamily Arachnidioidea has particularly been neglected concerning detailed morphological and histological details. So far, not a single analysis specifically studied a representative of the family Arachnidiidae. Arachnidium-like forms have, however, often been regarded as potential cheilostome ancestors, the most successful group of bryozoans to date. The lack of any morphological data on this family called for a detailed investigation of one of its representatives. Hence, we analysed the general morphology and histology of Arachnidium fibrosum. Most striking morphological features previously unrecognized are a cardiac constrictor, previously almost unknown in the family, a single pair of apertural muscles consisting of proximal parieto-diaphragmatic and distal parieto-vestibular muscles, six pairs of duplicature bands, a lophophoral anus and retractor muscles attaching to the foregut. Although comparative data are limited, there seem to be two distinct different clades of arachnidiid ctenostomes that are characterized by their aperture and details of gut morphology. Further analysis of additional arachnidioidean species are required to confirm this.

We report the introduction of the encrusting bryozoan Watersipora subtorquata to Atlantic coasts of Europe. This species is highly invasive, having become common on coastlines throughout cool-temperate areas of the world since the 1980s. Confusion exists over the identity of this and other Watersipora species, which lack characters that are conventionally used in bryozoan systematics. W. subtorquata has not been well distinguished from W. cucullata which, reports dating back to the mid 1800s suggest, is native to the Mediterranean Basin or represents an early shipping introduction. W. cucullata has been placed in synonymy with W. subovoidea, a taxon lacking a holotype. We designate a neotype for W. subovoidea, recognizing its conspecificity with W. cucullata, and demonstrate a simple morphometric means of separating this species from W. subtorquata using zooid feature ratios (operculum area versus total frontal shield). An orange watersiporid population that was first recognized in Guernsey, in the European-Atlantic, in 2007, is shown by morphometric and mitochondrial genetic analysis to match W. subtorquata. It contains the commonest, widely introduced COI haplotype that, along with other evidence, suggests recent transfer via shipping traffic to Europe. A second population (previously referred alternatively to W. aterrima or W. subovoidea) has been reported from Brittany and Bordeaux (Atlantic coastline, France). This population is also aligned with W. subtorquata based on morphometrics and COI haplotype. In contrast to the Guernsey introduction, the earlier French-Atlantic introduction appears related to oyster imports from Japan.

The invasive ctenophore, Mnemiopsis leidyi, which had its first mass occurrence in Limfjorden (Denmark) . During that period, copepods and other mesozooplankton organisms were virtually absent while ciliates were a substantial part of the zooplankton biomass. In "pre-Mnemiopsis years", there seems to have been large variability in the grazing impact on zooplankton depending on the seasonal abundance of A. aurita. With the addition of the second carnivore M. leidyi, however, additional predation pressure caused the zooplankton stocks to be severely depressed throughout 2008 and 2009 when copepods and cladocerans no longer showed the high seasonal peaks in abundance typical of previous years.

Ctenostome bryozoans are unmineralized and mostly marine. Their lack of calcified skeletal features requires other characters to be considered for systematic and phylogenetic considerations. As a continuation of an ongoing series of studies, we herein investigate the morphology of Amphibiobeania epiphylla, a unique bryozoan inhabiting mangrove leaves that are highly exposed to tidal cycles and regular dry events according to the tidal cycle. Besides this interesting mode of life, the species was originally interpreted to be a weakly mineralized cheilostome bryozoan, whereas molecular data place it among ctenostome bryozoans. To elucidate the systematic and phylogenetic position of the genus and also find morphological adaptations to an extreme habitat, we investigated the morphology of A. epiphylla in detail. Zooids show a lophophore with eight tentacles and a simple gut with a prominent caecum, lophophoral anus and most notably a distinct gizzard in the cardiac region. Gizzard teeth are multiple, simple homogeneous cuticular structures. The cuticle of the zooid is rather uniform and shows no respective thickenings into opercular flaps or folds.Likewise, apertural muscles are represented by a single pair of muscles. There are no specific closing muscles in the apertural area like the operculum occlusors of cheilostomes. Most prominent within zooids is a spongiose tissue filling most of the body cavity. Although not properly understood, this tissue may aid in keeping animals moist and hydrated during prolonged dry times. In summary, all morphological characters support a ctenostome rather than a cheilostome affinity, possibly with Vesicularioidea or Victorelloidea. In addition, we provide new molecular data that clearly supports such a closer relationship.