Colony Growth Pattern in Electra pilosa (Linnaeus) and Comparable Encrusting Cheilostome Bryozoans

Colony growth pattern is described in E. pilosa, an abundant cheilostome bryozoan commonly found as an epiphyte of Laminaria. Each zooid has 4 potential budding loci—one distal, two lateral and one proximal. The ancestrula buds daughter zooids from all of these loci; the two lateral buds appear first, followed by the distal bud and, after a long delay, the proximal bud. The laterally budded zooids curve inwards as they grow to form a triad with their distally budded sibling zooid. ‘Mature’ multiserial colonies growing on flat substrata consist of a series of radially diverging sectors. Each sector has an axis, generally of 3 parallel rows of zooids, flanked by wings consisting of rows of zooids originating as lateral buds from the section axis which infills the area between the axes. Occasional colonies occur with uniserial or semiuniserial growth patterns. These resemble colonies of the obligatory uniserial species Pyripora catenularia and poorly fed colonies of the related Conopeum tenuissimum, which is normally multiserial like E. pilosa. The ‘composite multiserial’ colonies of E. pilosa differ in several respects from ‘unitary multiserial’ colonies characteristic of most sheet-like cheilostomes, including the well-known Membranipora membranacea. Composite and unitary multiserial growth patterns may have evolved independently from uniserial ancestors.     

Polymorphism and vestigiality: comparative anatomy and morphology of bryozoan avicularia

Avicularia are polymorphic zooids characteristic of cheilostome bryozoans. Avicularia are assumed to have a defensive role yet ascertaining the presence of sensory structures to support this theory has been overlooked. We examine palatal morphology of the avicularia from five species of cheilostome bryozoans and compare the ultrastructural anatomy of the avicularia from two bugulid species from different habitats. SEM analysis revealed an array of palatal morphologies. Small tufts of cilia emerge from the orifice in the palate of the avicularia of Tricellaria catalinensis, Arachnopusia unicornis and Catenicella pseudoelegans. A ciliated vestigial polypide emerges from the orifice in the palate of Rhynchozoon zealandicum and comprises eleven papillae, or vestigial tentacles, seven of which are covered in microvilli. The vestigial polypide of the bird’s head avicularium of the cosmopolitan Bugula flabellata consists of a mass of ciliated and unciliated cells containing numerous granular vesicles. The avicularium of B. flabellata is capable of detecting tactile stimulation by virtue of the tuft of sensory cilia and is proactive in the capture of invertebrate epibionts. In contrast, in the deep-sea Nordgaardia cornucopioides, the vestigial polypide consists of a ciliated vestigial tentacle encased by glandular secretory cells. Avicularia possess structures derived from a feeding autozooid, and we show how the homologous structures have evolved and suggest that avicularia have been modified to carry out a variety of specific functions.     

Comparative anatomical study of internal brooding in three anascan bryozoans (Cheilostomata) and its taxonomic and evolutionary implications

The anatomical structure of internal sacs for embryonic incubation was studied using SEM and light microscopy in three cheilostome bryozoans-Nematoflustra flagellata (Waters,1904), Gontarella sp., and Biflustra perfragilis MacGillivray, 1881. In all these species the brood sac is located in the distal half of the maternal (egg-producing) autozooid, being a conspicuous invagination of the body wall. It consists of the main chamber and a passage (neck) to the outside that opens independently of the introvert. There are several groups of muscles attached to the thin walls of the brood sac and possibly expanding it during oviposition and larval release. Polypide recycling begins after oviposition in Gontarella sp., and the new polypide bud is formed by the beginning of incubation. Similarly, polypides in brooding zooids degenerate in N. flagellata and, sometimes, in B. perfragilis. In the evolution of brood chambers in the Cheilostomata, such internal sacs for embryonic incubation are considered a final step, being the result of immersion of the brooding cavity into the maternal zooid and reduction of the protecting fold (ooecium). Possible reasons for this transformation are discussed, and the hypothesis of Santagata and Banta (Santagata and Banta1996) that internal brooding evolved prior to incubation in ovicells is rejected.     

Zooid size and growth rate of the bryozoan Cryptosula pallasiana Moll in relation to temperature, in culture and in its natural environment

The size of cheilostome bryozoan zooids has been widely discussed for its potential in inferring palaeotemperatures, based on correlations between zooid size and temperature. Studies in both the natural environment and under experimental laboratory conditions have shown that an increase in temperature significantly decreases zooid size in a range of bryozoan taxa. In order to test the effect of temperature on zooid size, the cheilostome bryozoan Cryptosula pallasiana was for the first time successfully cultured under laboratory conditions. C. pallasiana was grown at 14 °C and 18 °C using Rhodomonas sp. as a food organism. Zooid size, tentacle number and growth rate were measured over a period of 26 days. For comparison, zooids from colonies of C. pallasiana collected from the natural environment were measured in winter and summer months. Results showed that colonies grown in laboratory culture had significantly longer and wider zooids at 14 °C than at 18 °C. The specific growth rate of C. pallasiana doubled from 14 °C to 18 °C. Comparison of tentacle number in culture showed a significantly higher value at lower temperatures. This may be related to differing food availability, longer polypide life spans, or a shift of energy use at colder temperatures. In nature the zooids were significantly longer in colonies sampled in July than in January, a clear difference from laboratory results. The utility of cheilostome Bryozoa as indicators of environmental change and their potential for studies of paleotemperature are highlighted.     

Prudent female allocation by modular hermaphrodites: female investment is promoted by the opportunity to outcross in cyclostome bryozoans

Many sessile, suspension‐feeding marine invertebrates mate by spermcasting: aquatic sperm are spawned and gathered by conspecific individuals to fertilize eggs that are generally retained during development. In two phylogenetically distant examples, a cheilostome bryozoan and an aplousobranch ascidian, the receipt of allosperm has previously been shown to alter sex allocation by triggering female investment in eggs and brooding. Here we report experiments demonstrating that two species of cyclostome bryozoan also show restrained female investment in the absence of mating opportunity. In Tubulipora plumosa, the production of female zooids and progeny is much reduced in reproductive isolation. In Filicrisia geniculata, development of distinctive female zooids (gonozooids) begins but halts in the absence of mating opportunity, and no completed gonozooids or progeny result. Reduced female investment in the absence of a mate thus occurs in at least two orders of Bryozoa, but significant differences in detail exist and the evolutionary history within the phylum of the mechanism(s) by which female investment is initiated might be complex. The broadening taxonomic spectrum of examples where female investment appears restrained until allosperm becomes available may signify a general adaptive strategy among outcrossing modular animals, analogous to similarly adaptive sex allocation typical of many flowering plants.     

Variation in reproductive characteristics of colonies of the freshwater bryozoan Cristatella mucedo

1. We studied relationships between different forms of reproduction and local variation in the reproductive state of colonies of a common freshwater bryozoan Cristatella mucedo Cuvier (Bryozoa: Phylactolaemata). Four sampling locations in central Finland, including both lotic and lentic habitats, were sampled by scuba diving. The traits studied were occurrence of sexual larvae, colony size, number of resting stages (statoblasts) and number of zooids. 2. While 76.9% of the sampled colonies carried statoblasts at the time of sampling, only 4.5% of the colonies were brooding sexual larvae. Most of the colonies were relatively small with a mean colony size of 16.6 mm. 3. In colonies brooding larvae, the number of statoblasts was positively correlated with the number of larvae. We did not detect a colony size threshold for sexual reproduction or formation of statoblasts. Colonies carrying statoblasts had a lower number of zooids per unit dry weight. 4. We found significant variation in reproductive traits of colonies among the sampling locations, and among lotic and lentic habitats. The observed phenotypic differences may reflect broadly distributed, phenotypically plastic clones. Differences in clonal composition of local populations cannot, however, be ruled out and factors that may provide clonal diversity are discussed.     

Zooid individuality and brooding organs (Bryozoa)

Summary In the Bryozoa neither an extreme accentuation nor an extreme denial of the individuality of the zooids in the colonies is in accordance with the observed facts. The brooding organs of the Gymnolaemata have developed independently from the brooding organs of the Phylactolaemata.     

Skeletal alterations and polymorphism in a Mediterranean bryozoan at natural CO<Subscript>2</Subscript> vents

Colonies of the cheilostome bryozoan Schizoporella errata were grown at a site near Ischia Island (Tyrrhenian Sea, Italy) where volcanogenic CO₂ emissions lower seawater pH to 7.76, simulating levels of ocean acidification predicted for the end of the present century. Compared with colonies from a control site (mean pH = 8.09), putative defensive polymorphs (avicularia) were significantly fewer, and retarded growth of zooidal basal and lateral walls was evident at the low pH site. The lower proportion of avicularia suggests a switch in resource allocation away from defence to favouring rapid growth. In addition, corrosion of the skeleton was observed in both new and old zooids at the low pH site, and feeding zooids were slightly smaller but had larger orifices for the protrusion of feeding lophophores. These findings corroborate previous studies demonstrating potential dissolution of carbonate skeletons in low pH seawater, while providing new insight into the possible ability of colonial species to respond to ocean acidification by adjusting resource allocation between zooids of different types.     

Sexual reproduction of the placental brooder Celleporella hyalina (Bryozoa,Cheilostomata) in the White Sea

The evolution of parental care is a central field in many ecological and evolutionary studies, but integral approaches encompassing various life-history traits are not common. Else, the structure, development and functioning of the placental analogues in invertebrates are poorly understood. Here, we describe the life-history, sexual colony dynamics, oogenesis, fertilization and brooding in the boreal-Arctic cheilostome bryozoan Celleporella hyalina. This placental brooder incubates its progeny in calcified protective chambers (ovicells) formed by polymorphic sexual zooids. We conducted a detailed ultrastructural study of the ovary and oogenesis, and provide evidence of both auto- and heterosynthetic mechanisms of vitellogenesis. We detected sperm inside the early oocyte and within funicular strands, and discuss possible variants of fertilization. We also detail the development and functioning of the placental analogue (embryophore) in the various stages of embryonic incubation as well as embryonic histotrophic nourishment. In contrast to all known cheilostome placentas, the main part of embryophore of C. hyalina is not a single cell layer. Rather, it is a massive “nutritive tissue” whose basal part is associated with funicular strands presumably providing transport function. C. hyalina shows a mixture of reproductive traits with macrolecithal oogenesis and well-developed placenta. These features give it an intermediate position in the continuum of variation of matrotrophic provisioning between lecithotrophic and placentotrophic cheilostome brooders. The structural and developmental differences revealed in the placental analogue of C. hyalina, together with its position on the bryozoan molecular tree, point to the independent origin of placentation in the family Hippothoidae.     

The distribution of colonies of the bryozoan Antarctothoa bougainvillei on the red alga Hymenena laciniata

The cheilostome bryozoan Antarctothoa bougainvillei (d’Orbigny) is the most frequent epibiont on the ribbon-like red alga Hymenena laciniata (Hooker f. & Harvey) Kylin in San Sebastián Bay (Tierra del Fuego, Argentina). Twenty-one thalli and 1,484 colonies were examined to analyse the relationship between both species. In most cases, number and area of colonies did not differ significantly at both sides of the thallus. Ancestrulae (i.e., founder zooids originating colonies by asexual budding) were mostly oriented facing the algal growing edge. Colonies were more frequent on central than on marginal zones of the thalli. The population of A. bougainvillei was mainly composed of very small colonies (<10 mm²). Larger colonies predominated and intraspecific competition was more intense near the basal portions of the thalli. Fecundity (number of ovicells) increased at a significantly higher rate in colonies with margins obstructed by conspecific neighbours than in free-growing colonies. Colonies were significantly larger on somatic than on reproductive algal tissues. As total and reproductive surfaces covered by colonies of A. bougainvillei were on average very low (4.43% and 0.53%, respectively), this epibiont is not supposed to produce a negative effect on H. laciniata. Handling editor: T. P. Crowe     

Operculate cyclostome bryozoans (Eleidae) from the Bohemian Cretaceous

Eleidae (‘melicerititids’) are unusual cyclostome bryozoans possessing operculate zooids and mandibulate polymorphs (‘eleozooids’) resembling the avicularia of cheilostome bryozoans. Here we describe 13 eleid species from the Cenomanian-Turonian of the Bohemian Cretaceous basin in the Czech Republic. Three species of Meliceritites are new: Meliceritites kankensis, M. stillativa and M. upohlavyensis. Reptoforicula gen. nov. is introduced for free-walled eleids with multilamellar encrusting colonies, containing the type species Reptoforicula zbyslavensis sp. nov. and R. vodrazkai sp. nov. Type specimens of three species erroneously assigned to Eleidae are refigured and their true affinities discussed. This study underscores the value of eleozooids in distinguishing between otherwise closely similar eleid species. The Bohemian late Cenomanian-early Turonian eleid fauna is dominated by encrusting species, a pattern that is typical of nearshore localities and contrasts with offshore chalks where erect, vincularian species are more numerous.     

Comparative anatomy of internal incubational sacs in cupuladriid bryozoans and the evolution of brooding in free‐living cheilostomes

Numerous gross morphological attributes are shared among unrelated free‐living bryozoans revealing convergent evolution associated with functional demands of living on soft sediments. Here, we show that the reproductive structures across free‐living groups evolved convergently. The most prominent convergent traits are the collective reduction of external brood chambers (ovicells) and the acquisition of internal brooding. Anatomical studies of four species from the cheilostome genera Cupuladria and Discoporella (Cupuladriidae) show that these species incubate their embryos in internal brooding sacs located in the coelom of the maternal nonpolymorphic autozooids. This sac consists of a main chamber and a narrow neck communicating to the vestibulum. The distal wall of the vestibulum possesses a cuticular thickening, which may further isolate the brood cavity. The presence of this character in all four species strongly supports grouping Cupuladria and Discoporella in one taxon. Further evidence suggests that the Cupuladriidae may be nested within the Calloporidae. Based on the structure of brooding organs, two scenarios are proposed to explain the evolution of the internal brooding in cupuladriids. The evolution of brood chambers and their origin in other free‐living cheilostomes is discussed. Unlike the vast majority of Neocheilostomina, almost all free‐living cheilostomes possess nonprominent chambers for embryonic incubation, either endozooidal and immersed ovicells or internal brooding sacs, supporting the idea that internal embryonic incubation is derived. We speculate that prominent skeletal brood chambers are disadvantageous to a free‐living mode of life that demands easy movement through sediment in instable sea‐floor settings. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Two new species of Electra (Bryozoa, Cheilostomata) from the Miocene of the Aquitaine Basin, France

Post-Cretaceous examples of Electridae, a primitive family of cheilostome bryozoans, are poorly represented in the fossil record, probably because of their thinly calcified zooids and preference for nearshore environments. Two new electrid species are here described from the Lower Miocene (Burdigalian) of Pontpourquey, Aquitaine, France: Electra triaurata nov. sp. and Electra aquitanica nov. sp. Both species belong to extant species groups, the E. indica and E. biscuta groups, respectively, that presently occur in the Indo-Pacific; both are the only fossil examples of these species groups. Whereas E. triaurata nov. sp. has uniserial colonies, zooids with porous gymnocysts, three flattened spines and basal windows allowing etching of the substrate to produce the trace fossil Leptichnus, E. aquitanica nov. sp. has multiserial colonies and zooids with a proximal gymnocyst bearing 2 to 5 spines.     

Epidermal structure of the scleractinian coral Mycetophyllia ferox: light-induced vesicles,copious mucocytes,and sporadic tentacles

Three colony fragments of the scleractinian coral Mycetophyllia ferox Wells from Florida were observed in flow-through seawater aquaria under light and dark conditions. The colonies were then anesthetized and fixed for microscopic examination. Small vesicles formed across the epidermis in response to light as gastrodermis containing approximately 1.9 × 10⁶ zooxanthellae cm⁻² migrated into them. The vesicles flattened in the dark and the gastrodermis retreated to a clumped position. The epidermis is dominated by mucus cells with more than 6300 per mm². In contrast, there are very few epidermal cnidae. The polyps lack tentacles entirely, though small tentacles do occur, albeit sporadically, along the colline walls. Colline tentacles are expanded both day and night, and there is considerable intracolonial variability in the number of cnidae within them, ranging from as few as 316 to more than 3200 per mm² tentacle. There may be several small cnidocyst batteries containing both spirocysts and nematocysts (all microbasic p-mastigophores), but the principal battery is at the tentacle tip where cnidae are much more densely packed. There is considerable variation in the ratio of the two cnidae among tentacles in the same colony. Since the tentacles occur inconsistently and do not appear to expand, their functional role is unclear. Comparisons of epidermal characters are made with other members of the genus Mycetophyllia.     

拟柄突和平水母在中国的首次发现及其生活史观察

报道青岛海洋科技馆培养的和平水母属(软水母亚纲,和平水母科)一种我国的新纪录--拟柄突和平水母西 Eirene lacteoides Kubota and Horita,1992.首次提供该种水母水螅体的形态,并对各期水母体的特征进行描述,为编写水螅水母动物志提供参考.     

Functional significance of contrasting colony form in two mesozoic encrusting bryozoans

Mesozoic bryozoan faunas are dominated by two cyclostome form-genera, Stomatopora and Berenicea. Encrusing colonies of Stomatopora and Berenicea are respectively linear with zooids arranged in branching uniserial rows, and discoidal with zooids arranged in a multiserial sheet. Functional morphological analysis indicates that Berenicea colonies were physiologically and hydrodynamically better integrated than Stomatopora colonies and were also more successful at competing for substrate space. However, Stomatopora colonies had the abilitu to locate spacial refuges where mortality was decreased. The comparatively opportunistic mode of life inferred for Stomatopora is substantiated by apparent absence of larval brooding. Stomatopora was propably an early successional genus normally replaced by Berenicea during later ecological succession except in palaeoenvironments experiencing high levels of disturbance. Stomatopora is more like to have been ancestral to Berenicea than vice-versa.     

Pseudolunularia gen.n. (Cheilostomata), a IunuIitiform bryozoan from the Indo-West Pacific

A new genus of anascan lunulitiform bryozoan, Pseudolunularia . is introduced for two new species, P. enigma and P. unguis . It is inferred that live colonies both possess basal rhizoids and are supported and stabilized by elongate avicularian mandibles. The autozooids, brooding zooids and avicularia of both species bear a striking resemblance to a parallel pair of species belonging to the genus Lunularia, L. repandus and L. cupulus .     

Developmental pattern of colonies in the polystyelid ascidian,Polyandrocarpa misakiensis

Summary

The growth pattern of zooids formed asexually by budding was studied in the colonial ascidian, Polyandrocarpa misakiensis. Each colony started from a blas- tozooid (the first generation) on the glass plate in two series of experiments. To evaluate the growth of colonies, lineage of all the zooids of three successive generations was traced on photographs which were taken once a week. The zooids of the first generation produced many buds from any basal margin of the zooidal body, and those of the second generation produced a small number of buds mainly from anterior parts of the zooidal body. The zooids of the second generation produced by early budding of mother zooids were clearly more prolific than those produced by late budding. Circular colonies which developed around a zooid of the first generation consisted of stratified zones of successive generations. Each zone was composed of two subzones; the outer one mainly containing early-produced zooids, and the inner one mainly containing late-produced zooids. The zooids in the marginal area of colony are early-produced ones from generation to generation. The seawater temperature may influence the growth of zooids and/or the frequency of budding.     

Studies on Japanese botryllid ascidians. IV. A new species of the genus Botryllus with a unique colony shape, from the vicinity of Shimoda

The morphology and life history of a strange and unidentified botryllid ascidian were investigated. This ascidian was first collected from the stony shore of Ebisu Island in Shimoda, a city on Izu peninsula in central Japan. Unlike other botryllid ascidians, whose colonies are flat and smooth, this ascidian's colonies are rugged. In each colony, zooids are arranged into several oval systems, each of which has a thick part containing zooids and very thin parts that do not. The arrangement of ovary and testis in this species is the same as in other species of the genus Botryllus; the ovary is situated anterior to the testis. The embryo of this ascidian develops in the peribranchial cavity of its mother zooid without any brooding organs, as is the case with Botryllus scalaris and Botryllus puniceus. Meanwhile, the results of cut colony assay experiments did not show the existence of colony specificity in this ascidian. Even when two syngeneic colonies were brought into contact at their growing edges, none fused together. On the other hand, when two colonies were brought into contact with each other at their cut surfaces, they always fused into a single colony, regardless of their origin. Therefore, this species may be the only species that lacks colony specificity among the botryllids studied so far.     

A rare form of frontal shield development in the new cheilostome bryozoan genusUharella from the Eocene of Antarctica

A new cheilostome bryozoan,Uharella seymourensis n. gen., n. sp., is described from the Eocene of Seymour Island, Antarctic Peninsula. Colonies ofU. seymourensis encrust lithoclasts, locally in high densities with 1–2 mm-wide strips of unencrusted substrate between neighbouring colonies. This unusual patterning could indicate chemical defence against encroaching colonies or may have resulted from grazing.U. seymourensis is an ascophoran-grade cheilostome with an unusual umbonuloid frontal shield apparently derived entirely or in part from kenozooidal overgrowth. The most closely related genus appears to be the European Maastrichtian and Danian genusBrydonella Berthelsen, 1962 with whichUharella is here united in Brydonellidae n. fam.