Serotonergic and FMRFamidergic nervous systems in gymnolaemate bryozoan larvae

A growing body of data from nervous systems of marine invertebrate larvae provides an ideal background for comparisons among higher taxa. The currently available data from Bryozoa, however, do not allow for a consistent hypothesis of an ancestral state for this taxon, which would be necessary for phylogenetic inferences. The larval nervous systems of the four gymnolaemate species Flustrellidra hispida, Bugula fulva, Alcyonidium gelatinosum, and Bowerbankia gracilis are examined by means of antibody staining against the neurotransmitters serotonin and FMRFamide, as well as against acetylated α-tubulin. Despite considerable variation, a comparison reveals a common pattern of the distribution of serotonin. The neurotransmitter is found in at least two cells in the apical organ as well as in paired axial and lateral nerves emerging from a central nerve nodule. A ring nerve is present below the corona and at least two serotonergic cells are found between the corona cells. Serotonergic coronal cells might represent unique bryozoan features, whereas the remaining elements show resemblance to the situation found in most spiralian taxa. The data do not provide support for a closer relationship of Bryozoa to Phoronida or Brachiopoda.     

Global diversity of bryozoans (Bryozoa or Ectoprocta) in freshwater

The present study considers 88 bryozoan species occurring in freshwater: 69 phylactolaemate and 19 gymnolaemate species. Roughly 49% of these species are confined to one zoogeographical region. The cosmopolitan status of species like Fredericella sultana, Plumatella repens or P. emarginata has to be reconsidered. Among the Phylactolaemata, which are phylogenetically older than the Gymnolaemata, the gelatinous species (Lophopodidae, Pectinatellidae, Cristatellidae) are more primitive than the branching tubular species (Plumatellidae, Fredericellidae). Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

Ultrastructural study of metamorphosis in the freshwater bryozoan Plumatella fungosa (Bryozoa,Phylactolaemata)

Summary

At metamorphosis the attachment of the Plumatella larva to the substrate is effected by secretions from glandular cells in the apical plate, the leading pole during swimming. The larval mantle folds back and slides down towards the substrate. By ciliary activity an adhesive secretion is spread over the metamorphosing larva and the attachment area. Two polypides appear through the larval terminal opening. The mantle fold, together with gland cells, nerve cells, sensory cells, and muscle cells from the larva form a nutritive cell mass. Reduction of this nutritive cell mass is accomplished by autolysis and phagocytosis. An invaginated area of the nutritive cell mass is provided with a dense layer of microvilli, which seem to have an absorbtive function. The nutritive cell mass consisting of transitory larval tissues provides a significant source of nutrient for the developing polypide buds.     

Systematic studies on some Antarctic and sub-Antarctic Ascophora (Bryozoa: Cheilostomata)

Twenty-two species of ascophoran cheilostome Bryozoa are described and figured from Antarctic and sub-Antarctic localities. Ten new species are described in the genera Exochella, Buffonellodes and Hippadenella. Ralepria gen. nov. is introduced for Ralepria conforma sp. nov., and Trilochites gen. nov. is introduced for Escharoides biformata Waters, 1904. Five species described by Jullien (1888) and Calvet (1909) are redescribed following re-examination of type specimens.     

Systematic notes on some British Ascophora (Bryozoa: Cheilostomata)

A review of the British ascophoran cheilostomes has revealed several instances of synonymic confusion, and necessitated the introduction of two new generic names. Porelloides gen. nov. is instituted for two species formerly included in Porella , with P. laevis (Fleming) as type species, and Phaceostachys gen. nov. is introduced for Lepralia spinifera Johnson. Smittoidea amplissima sp. nov. was hitherto not distinguished from Smittina landsborovii (Johnston). Porella minuta (Norman), reported from localities as far afield as the western Mediterranean and the Canadian Arctic, is shown to comprise two species, and the northern records are here attributed to P. alba Nordgaard. Exharella labiosa (Busk) and E. klugei sp. nov. (=E. ventricosa var. peristomata Kluge) are redescribed, and E. laqueata and E. abyssicola are discussed. The case for retaining Cellepora Linnaeus is argued and Lepralia quincuncialis Norman is referred to Buskea Heller.     

Ultrastructure of mesoderm formation and development in Membranipora membranacea (Bryozoa: Gymnolaemata)

Mesoderm origin in Bryozoa is largely unknown. In this study, embryonic and early larval stages of Membranipora membranacea, a bryozoan exhibiting a planktotrophic cyphonautes larva, are investigated using mainly ultrastructural techniques. Shortly after the onset of gastrulation, an ectodermal cell, which is situated centrally at the prospective anterior pole of the larva, can be recognized by its constricted apical surface and enlarged basal part. It is also distinct from other ectodermal cells by the composition of its cytoplasm. In later stages, it has left the epidermis, lost its epithelial character, and is situated subepithelially, between the basal sides of the ectodermal and endodermal sheets. A blastocoelic cavity is not present at this stage. This cell divides and gives rise to a group of cells forming a muscular and neuronal strand at the anterior side of the larva. The majority of the larval musculature originates from this ingression. Despite this evidence for an ectodermal origin, additional sources of mesoderm can so far not be excluded. The literature on mesoderm origin in Bryozoa is reviewed and the results are compared to known data from other metazoan taxa.     

Ultrastructure of the body cavities in Phylactolaemata (Bryozoa)

Only species belonging to the bryozoan subtaxon Phylactolaemata possess an epistome. To test whether there is a specific coelomic cavity inside the epistome, Fredericella sultana, Plumatella emarginata, and Lophopus crystallinus were studied on the ultrastructural level. In F. sultana and P. emarginata, the epistome contains a coelomic cavity. The cavity is confluent with the trunk coelom and lined by peritoneal and myoepithelial cells. The lophophore coelom extends into the tentacles and is connected to the trunk coelom by two weakly ciliated coelomic ducts on either side of the rectum. The lophophore coelom passes the epistome coelom on its anterior side. This region has traditionally been called the forked canal and hypothesized to represent the site of excretion. L. crystallinus lacks an epistome. It has a simple ciliated field where an epistome is situated in the other species. Underneath this field, the forked canal is situated. Compared with the other species, it is pronounced and exhibits a dense ciliation. Despite the occurrence of podocytes, which are prerequisites for a selected fluid transfer, there is no indication for an excretory function of the forked canal, especially as no excretory porus was found. J. Morphol. 2009. © 2008 Wiley‐Liss, Inc.     

Asajirella gelatinosa in Panama: a bryozoan range extension in the Western Hemisphere (Ectoprocta: Phylactolaemata)

Asajirella gelatinosa, a freshwater bryozoan known previously only from eastern Asia is now reported in the Republic of Panama. Colonies were collected during April 1992 in the broad reaches of the lower Río Chagres as it enters Gatun Lake, part of the Panama Canal system. A subsequent collection in 1998 included large colonies and numerous statoblasts from a region upstream of this site in the impounded Lago Alajuela (Madden Lake). Colonies and statoblasts resemble those from Japan in almost every detail. Human transport of statoblasts is a likely cause of this disjunct distribution. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Recent species of Adeonella (Bryozoa: Cheilostomata) including descriptions of fifteen new species

The genus Adeonella Busk (1884) comprises 41 species, 15 of which are considered to be new to science. Adeonella lichenoides (Lamarck) is regarded as the senior synonym of A. platalea (Busk) (= A. polymorpha Busk), the type species of the genus. Adeonella is distributed throughout the Indo-West Pacific realm, the Mediterranean, and the South Atlantic Ocean. Its highest diversity is found off the east coasts of southern Africa. Thirty-one species (15 new to science) are described and illustrated, morphology and geographical distribution are discussed and a key is provided to all recognized species.     

Ultrastructure and Development of the Ooecial Walls in Some Calloporid Bryozoans (Gymnolaemata: Cheilostomata)

In the brood chambers (ovicells) of six calloporid cheilostomes studied each skeletal wall consists of four calcified layers: (1) a very thin superficial layer of planar spherulitic crystallites, (2) an upper (outer) layer with wall-perpendicular prismatic ultrastructure, (3) an intermediate lamellar layer, and (4) a lower (inner) wall-perpendicular prismatic layer. Comparative studies of both the ovicell wall ultrastructure and early ovicell formation showed a hypothetical opportunity for evolving complex (multilayered) skeletal walls by fusion of the initially separated gymnocystal and cryptocystal calcifications in Cheilostomata. In two species studied, a bilobate pattern in the final stage of the formation of the ooecial roof was encountered in specimens with the cuticle preserved. A possible explanation to this finding is discussed – the bilobate pattern is suggestive of the hypothetical origin of the brood chamber from (1) two flattened spines, or (2) reduction in spine number of an originally multispinous ovicell.     

The somatic musculature of Bryceella stylata (Milne, 1886) (Rotifera: Proalidae) as revealed by confocal laser scanning microscopy with additional new data on its trophi and overall morphology

The monogonont rotifer Bryceella stylata was investigated with light, electron and confocal laser scanning (CLSM) microscopy to provide detailed insights into its anatomy and new information for future phylogenetic analyses of the group. Results from CLSM and phalloidin staining revealed a total of six paired longitudinal muscles (musculi longitudinales I-VI) and eight circular muscles (musculi circulares I-VIII) as well a complex network of mostly fine visceral muscles. In comparison with other rotifer species that have been investigated so far, B. stylata shares the presence of the circular and longitudinal muscles: musculus longitudinalis ventralis, musculus longitudinalis lateralis inferior, musculus longitudinalis dorsalis, musculus longitudinalis capitis and musculus circumpedalis. However, the species lacks lateral and dorsolateral longitudinal muscles and some circular muscles (e.g., corona sphincter, musculus pars coronalis). With light and electron microscopy, we were able to document the precise number of pseudosegments and the arrangement of the chambers comprising the trophi elements. Furthermore, our observations revealed several new morphological characteristics, including a shield-like epidermal projection covering the dorsal antenna, an epidermal projection restricting the corona caudally and an unpaired hypopharynx with distinct shovel-like structures.     

Ultrastructure of the single-chamber stemmata of Arge pagana (Panzer, 1798) (Hymenoptera: Argidae)

Stemmata are peculiar visual organs of most larvae in holometabolous insects. In Hymenoptera, Symphyta larvae exclusively possess a pair of stemmata, whose cellular organizations have not been thoroughly elucidated to date. In this paper, the morphology and fine structure of stemmata were investigated in the large rose sawfly Arge pagana (Panzer, 1798) using light and electron microscopy. The larvae possess a pair of stemmata, which belong to the “unicorneal composite eye” or single-chamber stemmata. Each stemma is composed of a biconvex cornea lens, a layer of corneagenous cells, numerous pigment cells, and hundreds of retinula cells. According to the number of retinula cells forming a rhabdom, the stemma can be divided into two regions, the larger Region I and the smaller Region II. The former occupies the largest area of the stemma and contains the majority of rhabdoms, each of which is formed by the rhabdomeres of eight retinula cells. The latter occupies a narrow posterior margin, where each rhabdom consists of nine retinula cells. Based on the different cellular organizations of rhabdoms, the stemma of Argidae is likely developed by the fusion of two types of ommatidial units.     

Ganglion ultrastructure in phylactolaemate Bryozoa: evidence for a neuroepithelium

In contrast to other Bryozoa, members of the subtaxon Phylactolaemata bear a subepithelial cerebral ganglion that resembles a hollow vesicle rather than being compact. In older studies this ganglion was said to originate by an invagination of the pharyngeal epithelium. Unfortunately, documentation for this is fragmentary. In chordates the central nervous system also arises by an invagination-like process, but this mode is uncommon among invertebrate phyla. As a first attempt to gather more data about this phenomenon, cerebral ganglia in two phylactolaemate species, Fredericella sultana and Plumatella emarginata, were examined at the ultrastructural level. In both species the ganglion bears a small central lumen. The ganglionic cells are organized in the form of a neuroepithelium. They are polarized and interconnected by adherens junctions on their apical sides and reside on a basal lamina. The nerve cell somata are directed towards the central lumen, whereas the majority of nervous processes are distributed basally. Orientation of the neuroepithelial cells can be best explained by the possibility that they develop by invagination. A comparison with potential outgroups reveals that a neuroepithelial ganglion is at least derived. Since, however, a reliable phylogenetic system of the Bryozoa is missing, a decision on whether such a ganglion is apomorphic for Bryozoa or evolved within this taxon can hardly be made.