EFFECTS OF THE ENCRUSTING BRYOZOAN,MEMBRANIPORA MEMBRANACEA,ON THE LOSS OF BLADES AND FRONDS BY THE GIANT KELP,MACROCYSTIS PYRIFERA (LAMINARIALES)1

Juvenile sporophytes of the giant kelp, Macrocystis pyrifera (L.) C. A. Agardh, were transplanted from local kelp beds to stations located various distances from the outfall from an electrical generating station that was known to cause an increase in the settlement of fouling organisms. Plants near the outfall became heavily fouled by the encrusting bryozoan, Membranipora membranacea (L.), and lost about one-third of their blades during the course of the experiment. Blade loss was significantly correlated with amount of fouling. To test the hypothesis that fouling causes blade loss, we paired fouled and unfouled plants of about the same age, overall length, and number of fronds and placed them at stations in nearby kelp beds and near the outfall. At the stations in the kelp beds, the fouled plants lost blades more rapidly than the unfouled controls. However, at the station near the outfall the “control” plants quickly became fouled so there was little difference in treatments and there was no significant difference in blade loss. Plants fouled by Membranipora suffered greater blade loss than clean plants probably because fouled blades are fragile and break off easily and because fish bite off chunks of blade while foraging on the attached bryozoans.     

中国南部水域膜孔苔虫属一新种：苔藓动物门：唇口目：膜孔苔虫科

连壁膜孔苔虫Ｍｅｍｂｒａｎｉｐｏｒａｃｏｎｊｕｎｃｔｉｖａｓｐ．ｎｏｖ．群体被覆、单层。相邻个以隆起的个虫墙缘为界,无室间沟。横壁孔室单孔型,由大、中、小三种单孔组成。侧壁孔室多孔型,由一列大孔和列小孔组成。新种个虫一般形态与大室孔苔虫Ｍｅｍｂｒａｎｉｐｏｒａｇｒａｎｄｉｃｅｌｌａ的单层群体相似,但其权成相邻个虫的界限和体壁孔室的结构及排列方式与大室膜孔苔虫有显著区别。     

Density effects in a colonial monoculture: experimental studies with a marine bryozoan (Membranipora membranacea L.)

Summary Naturally occurring monocultures of plants and animals are not common, despite recent emphasis on the analysis of density effects in artificial plant monocultures. In natural populations, Membranipora membranacea, an encrusting marine bryozoan, usually forms monospecific, nearly even-aged stands on kelp blades. We experimentally manipulated the density of M. membranacea colonies and monitored the responses of individual colonies on settling panels. Colonies undergo a sub-annual cycle of growth, stasis and reproduction, shrinkage, and death. However, crowding by conspecifics accelerates the transition to stasis, triggers early onset of reproduction, and results in increased stage-specific mortality. Unlike many interactions involving colonial invertebrates, overgrowth rarely occurs at boundaries of M. membranacea colonies. Instead, colonies stop growing when they contact conspecifics; therefore more dense assemblages are populated with smaller individual colonies. At the peak in colony size during August, the mean size among colonies grown at high population densities was 300 mm² less than colonies grown at low densities or approximately 62% smaller. Mortality was concentrated in small size classes; at the end of the season colonies gradually shrank to the smallest size classes and then died. We summarized the demography of M. membranacea colonies on low- and high-density panels using size-classified transition matrices and used loglinear analysis to examine the effects of density and time on the transition patterns. As the amount of free space on panels declined, so did the frequency of upward size-class transitions. Our analysis revealed that free space declined more rapidly on panels in the high density treatment and that the transitional probabilities were sensitive to density of conspecifics and seasonal change, but only for some size classes and during some time periods.     

Biogeographic associations of Silurian bryozoan genera in North America, Baltica and Siberia

Six distinct bryozoan paleobiogeographical provinces existed during the Silurian of North America, Baltica and Siberia. These provinces are based on parsimony analysis of endemicity (PAE), each supported by a number of endemic genera only present in that assemblage. The area cladogram displays a nested pattern, permitting the clustering of assemblages into larger units that might be indicative of their areas of origin. Paired-group cluster analysis supports the existence of provincial assemblages. Relationships indicate the action of both vicariance and geodispersal. Geographic boundaries between the provinces include land, deep sea, and climate zone boundaries, including barriers created by the Iapetus Ocean and the Tornquist Sea.     

Thamniscus King, 1849 (Fenestellida: Bryozoa): William King’s original specimens and their bearing on the genus concept

Reassessment of the suite of specimens used by William King when he erected the fenestrate bryozoan genus Thamniscus in 1849 has shown that they belong to two genera. However, King’s original generic concept only allows for some of these specimens to be included within Thamniscus. These specimens are illustrated. A recent generic treatment is consistent with King’s original generic concept.     

New observations on the skeletons of the earliest bryozoans from the Fenhsiang Formation (Tremadocian,Lower Ordovician), Yichang,China

The earliest unequivocal bryozoans occurred in the Fenhsiang Formation (upper Tremadocian, Lower Ordovician) of Yichang, South China, providing important clues about the early evolution of primitive bryozoans. In this study, SEM and EDAX were used to analyze the microstructure of the walls of two bryozoan genera, Nekhorosheviella and Orbiramus, from the Fenhsiang Formation. All walls of Nekhorosheviella and endozonal walls of Orbiramus show poor preservation in thin sections, with a granular appearance reflecting extensive neomorphism, whereas exozonal walls of Orbiramus are distinctly laminated. These preservational differences may reflect skeletal chemistry, particularly the magnesium content of the calcite. Phosphatic skeletal linings were found to be distributed unevenly in the autozooecia of Nekhorosheviella, but were absent in Orbiramus.     

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.     

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.     

Estimating competition coefficients: strong competition among three species of frugivorous flies

Despite the abundance of studies on competitive interactions, relatively few experiments have been used to fit explicit competition models and estimate competition coefficients. Such estimates are valuable for making contact between theoretical and empirical studies, which tend to measure competition in different units. To quantify the strength of competitive interactions among the larvae of three species of frugivorous flies, I manipulated the densities of each species to investigate all three pairwise interactions. The densities of each species were changed independently (i.e., using a response surface experimental design), which allowed maximum likelihood estimation of the competition coefficients for each species, based on the Hassell and Comins competition model. The effects of competitor density on larval survival, time to emergence, and the weight of emerging adults were also analyzed to investigate the responses of individual species to density. The estimates of the competition coefficients suggest that the larvae of these flies experience strong asymmetric competition for resources, and raise questions as to how these species coexist. For each pair, one of the species was largely unaffected by interspecific competition, but decreased the performance of the other. Received: 8 February 1999 / Accepted: 5 April 1999     

Zooidal anatomy in Ordovician and Carboniferous trepostome bryozoans

Fossil bryozoans sometimes contain fossilised brown bodies which remain after polypide degeneration. Position and shape of brown bodies as well as different skeletal diaphragms within living chambers allow outlining of autozooid anatomy in Palaeozoic trepostome bryozoans. In some trepostome bryozoans short autozooids were restricted by complete basal diaphragms to distal parts of autozooecia. In species with alternating hemiphragms, as in the specimen ofHemiphragma sp. described here, long autozooids occupied the entire autozooecial chambers. Their short polypides were positioned in distal parts of the autozooid. Both anatomic types correspond to the progressive polypide cycle afterBoardman. For species with ring septa, non-alternating hemiphragms (studied in an example ofNipponostenopora karatauensis) as well as without any diaphragms the stationary type of polypide cycle seems also to be possible. In that case, the polypides should be as long as the cystid.      

The epizoic diatom community on four bryozoan species from Helgoland (German Bight, North Sea)

The composition of the diatom community on the bryozoans Electra pilosa, Membranipora membranacea, Flustra foliacea, and Alcyonidium gelatinosum from the German Bight was studied by light and scanning electron microscopy. In total, members of 26 diatom genera were found, with Cocconeis, Tabularia, Licmophora, Amphora, and Navicula being the most abundant. The amount and the composition of the diatom covering seem to be typical for single bryozoan species. Electra pilosa and Membranipora membranacea showed a rather dense covering with 71–547 cells/mm² and 77–110 cells/mm², respectively. The most prominent genus on Electra pilosa was Cocconeis, reaching up to 58% of all diatoms in one sample, followed by Navicula, Tabularia and Amphora. The most abundant genera on Membranipora membranacea were Tabularia and Licmophora, making up almost 70% of all diatoms in one sample, followed by Navicula, Cocconeis and Amphora. The diatom composition was very stable on all Electra samples, but varied on Membranipora samples. With <1–27 cells/mm², diatoms were much less abundant on Alcyonidium gelatinosum. Members of the genera Tabularia and Navicula were the most frequently found benthic diatoms, whereas the planktonic forms Coscinodiscus, Cyclotella, and Thalassiosira made up 35% of the diatoms. On Flustra foliacea, diatoms were virtually absent, with fewer than 5 cells/mm². The low diatom numbers are probably due to toxic metabolites produced by the host. The same may be true for Alcyonidium gelatinosum, but here they might also be a consequence of the surface properties of the bryozoan. Electronic Publication     

The polyphyletic origin of the "Cheilostomata" (Bryszoa)

The relative appearance of the parietal muscles in the development of the zooids has been studied in several ctenostomatous and “cheilostomatous” species. A comparison of the different on-togenetical sequences demonstrated that a “cheilostomatous” type of organization of the zooids with a great probability has been achieved in minimum three times independentl and originated from different ctenostomatous sub-grous: the Membranidea from plesiomorgic victorelloids (ancestors of Bulbella with not yet developed peristomial tube), the Inoviceiata (Aetea) from advanced forms of victorelloids with reduced primary parietal muscles (perhaps stcies related to Pottsiella), and Penetrantia from arachnidioid or vesicularioid ancestors (?). Therefore, the classical orders ^α“Ctenostomata” and “Cheilostomata” represent only “stage groups” but no monohyletic systematical units. Because of the new concept and interpretation I propose a new name for the united group: Cteno-Cheilostomata, supra-ord. nov.     

苔藓动物的起源与系统发生研究进展—形态学和分子生物学的证据

苔藓动物是后生动物中的一个重要类群。然而,和其它主要后生动物类群相比,长期以来对它的系统学研究却相对滞后。其起源,系统发生地位以及与其它后生物门类之间、其内部各高级分类群间的谱系发生关系一直存在争议。一般认为它是介于原口动物和后口动物之间的过渡类群。但是,近年来的分子系统学研究已经证实了它的原口归属。古生物学资料表明,虽然苔藓动物的大多数类群在奥陶纪已经分化出来,但它在寒武纪却缺乏任何化石记录。另外,苔藓动物起源的时间和方式、其内部各类群间的系统发生关系特别是现生类群和化石类群之间的关系等诸多问题的解决,还有待于大量的形态学和不同的分子数据的进一步积累,并结合其地层分布等各种相关资料进行综合研究。