Female genital structures of Metridinidae (Copepoda: Calanoida)

The female genital structures of six calanoid copepod species, belonging to the genera Gaussia, Metridia and Pleuromamma, were studied using light and scanning electron microscopy (SEM). The copulatory pores and seminal receptacles are paired in Gaussia and Metridia, but unpaired in Pleuromamma. A thin epicuticle and a spermatophoral plug are the mechanisms by which the pores are closed before and after copulation. The pores open directly into the receptacles, which are reduced to shallow integumentary depressions in Gaussia. The mode of insemination suggests two matings in females of Gaussia and Metridia, but only one in Pleuromamma. Paired gonopores and egg-laying ducts are present in the three genera, with a characteristic, closed semicircular configuration; these are opened during egg-laying by the action of retractor muscles of the gonoporal plates. The seminal ducts, which open into the gonopores, are long, thin and paired in Gaussia and Metridia, whereas in Pleuromamma they are short, broad and unpaired. The opening of the seminal and egg-laying ducts is synchronized. The shell ducts are paired in Gaussia and Metridia, unpaired in Pleuromamma; these arise from glands situated in the lateral expansions of the last prosomite and lead into the distal part of each egg-laying duct in Gaussia and Metridia and of the egg-laying duct receiving the seminal duct in Pleuromamma. The position and anatomy of these structures are compared to those of other families and genera, and a functional interpretation of their morphology is proposed. The main evolutionary trends of the different structural patterns of female calanoid genitalia are presented in tabular form. Received: 30 December 1996 / Accepted: 11 February 1997     

Turbulent air–water flows in hydraulic structures: dynamic similarity and scale effects

In hydraulic structures, free-surface aeration is commonly observed: i.e., the white waters. The air bubble entrainment may be localised (hydraulic jumps, plunging jets) or continuous along an interface (water jets, chutes). Despite recent advances, there are some basic concerns about the extrapolation of laboratory results to large size prototype structures. Herein the basic air bubble entrainment processes are reviewed and the relevant dynamic similarities are discussed. Traditionally, physical studies are conducted using a Froude similitude which implies drastically smaller laboratory Reynolds numbers than in the corresponding prototype flows. Basic dimensional analyses are developed for both singular and interfacial aeration processes. The results are discussed in the light of systematic investigations and they show that the notion of scale effects is closely linked with the selection of relevant characteristic air–water flow properties. Recent studies of local air–water flow properties highlight that turbulence levels, entrained bubble sizes and interfacial areas are improperly scaled based upon a Froude similitude even in large-size models operating with the so defined Reynolds numbers ρ _w × q _w/μ _w up to 5 E+5. In laboratory models, the dimensionless turbulence levels, air–water interfacial areas and mass transfer rates are drastically underestimated.     

Taxonomic revisions in the marine biflagellate fungi: The ultrastructural evidence

The ultrastructure of the genera Althornia, Aplanochytrium, Japonochytrium, Schizochytrium and Thraustochytrium is described, and all are regarded as members of the new order Thraustochytriales Sparrow. Species considered are Althornia crouchii, Aplanochytrium kerguelensis, Hyalochlorella marina, Japonochytrium sp., Schizochytrium aggregatum, Thraustochytrium kinnei and T. striatum. All but H. marina are, on ultrastructural evidence, related genera, and some speculative suggestions are made about possible interrelationships both between the species discussed, between the Thraustochytriales and Labyrinthulales, and between these two and other major taxa.     

A stereoscan electron microscope study of male reproductive characters in the Jaera albifrons group of species (Crustacea: Isopoda)

The male secondary sex characters of Jaera albifrons Leach, Jaera ischiosetosa Forsman, Jaera praehirsuta Forsman and Jaera forsmani Bocquet are described with the Stereoscan electron microscope (S.E.M.). These characters, which are present on the peraeopods, are the only means of identification for these Jaera species which together form the Jaera albifrons group (Isopoda, Asellota). The male praeoperculum (modified, fused, first pair of pleopods) and appendix masculinae (modified endites of the second pair of pleopods) have also been studied with the S.E.M. and possible functions of the various sex characters are discussed. Both the male operculum and appendix masculinae are similar for each species, suggesting that copulation with females of a different species is anatomically possible. The fact that hybrids are rarely collected in ecological investigations is discussed with reference to the present known information. Two methods of copulation for the members of this group have been proposed and these are discussed. A method of sperm transfer along the male operculum is outlined.     

Microbial associations in sponges. III. Ultrastructure of the in situ associations in coral reef sponges

Symbiotic cyanobacteria are associated with marine sponges in three ways: the majority are free-living in the mesohyl; large aggregates occur in cyanocytes (specialized, vacuolated archeocytes); and few are present in digestive vacuoles. The cyanobacteria in Jaspis stellifera and Neofibularia irata are morphologically similar to those described in Mediterranean sponges, whereas those in Pericharax heteroraphis are different. The freeliving bacterial populations are morphologically similar, although the number of bacteria varies between the species. The fourth sponge Ircinia wistarii contains a mixed bacterial population unlike those in the other sponges. Sponge digestion of microbial associates is rare and not considered to contribute significant nutrients.     

Notes on the Nerita (Archaeogastropoda) populations of Aldabra Atoll,Indian Ocean

Nerita undata, N. plicata, N. polita, N. albicilla and N. textilis are common intertidal gastropods on Aldabra Atoll. Each species prefers a different level on the shore and/or different degrees of exposure to wave action. Patterns of zonation, population size-frequency structure and biomass are given. N. undata exhibits 2 distinct ecophenotypes. Normal types occur on expsed to moderately sheltered shores but are replaced by type B in extremely sheltered conditions. Differences in shell morphology and population structure are also noted. Foraging by all species was confined to hours of darkness, generally at low tide. Activity of N. polita was induced slightly on overcast days. N. undata and N. textilis are cryptically coloured and often visible during the day. N. plicata is conspicuous, but is protected by a strong shell. N. polita and N. albicilla are often brightly and variably coloured, but both are concealed during daylight. No Nerita were found infected with trematodes, suggesting that the degree of infection was extremely low. Habitats of the Aldabran Nerita are compared with 3 species on Barbados, West Indies.     

Anchorage of embryos in Spirorbinae (Polychaeta)

Methods of incubation are taxonomically important in Spirorbinae. About half of the known species incubate in the operculum, but the remainder are usually described simply as incubating within the tube. Studies of tube incubation show that the embryos are anchored in various ways. They form an egg string, which is attached to the tube by a posterior filament in Spirorbis and Spirorbella; they adhere more generally to the tube wall in Circies and Paradexiospira; they are attached to specialised thoracic stalks in Protolaeospira, Helicosiphon and Romanchella; they adhere to the body surface in Metalaeospira and probably in Eulaeospira; they are not attached to either body or tube in Paralaeospira. Tube incubation is found predominantly in temperate or cold waters. In most species from the southern hemisphere, embryos are anchored to the bodies of the parents, but in most species from the northern hemisphere, embryos are fixed to the walls of the parent tubes.     

Mechanistic aspects of the thermal formation of halogenated organic compounds including polychlorinated dibenzo‐p‐dioxins. Part V†: Hypotheses and summary

The hypotheses on the de novo syntheses of polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo‐p‐dioxins (PCDDs), based on known literature, are presented. Polychlorinated benzenes and polychlorinated phenols are probably key intermediates.

In the present article, hypotheses that may account for the presence of polychlorinated dibenzofurans (PCDFs) and dibenzo‐p‐dioxins (PCDDs) in the effluents from municipal and industrial incinerators are put forward. These hypotheses are based on the previously surveyed literature (Ref. 203–206) and experimental results on laboratory scale and thermodynamic calculations are considered. The interconnections of various reaction steps are speculative and no technological information was added to account for conditions in real incinerators. Conclusion of the discussions on the related subject matter, presented in the Parts I‐IV (Ref. 203–206), are also described in this paper.     

A further contribution to the study of fish populations by capture-recapture experiments

In capture-recapture experiments, fish populations can be studied by two different sampling procedures. In both procedures, tagged fish are released on capture, but untagged fish are in one procedure released after tagging, in the second procedure they are retained. Using the two sampling techniques, Rafail (1971a,b) gave expressions for the estimation of an assumed constant (C) of proportionality between probabilities of capture of tagged to untagged fish which are simplified here to forms easier for calculation. The estimation of this constant (C) aids in estimation of abundance and mortality rates of untagged fish which are assumed to differ from those of tagged fish.     

The histology,histochemistry and ultrastructure of the cement apparatus of three adult sessile barnacles,Elminius modestus,Balanus balanoides and Balanus hameri

The histology, histochemistry and ultrastructure of the cement gland cells of 3 species of sessile barnacles are described. Cells of both Elminius modestus Darwin and Balanus balanoides (L.) (membranous bases) are similar histologically and ultrastructurally, and within the cells there are 2 distinct regions. One is the site of secretion accumulation, the other the site of secretion synthesis. In Balanus hameri Ascanius (calcareous base) the cells are different in that the cytoplasm is more homogeneous. In all 3 species protein is the final secretion product (cement) of the cement cells. The mode of discharge of secretion from the cells differs between the membrane based and calcareous based barnacles. In the former, there is a series of collecting canals within the cytoplasm of the cement cells (intracellular canals) which join with the larger extracellular cement ducts. Secretion passes into the intracellular canals and is moved along to the larger cement ducts, which have an inner chitin lining. In Balanus hameri (calcareous base) there are no intracellular collecting canals. Secretions are thought to pass from the cement cells into the cement duct cells direct. The cement ducts in this species are not chitin lined.     

Gametogenesis in Harmothoe imbricata (Polychaeta: Polynoidae)

The processes of gametogenesis in Harmothoe imbricata are described and illustrated. For most of their development the gametes are attached to the walls of segmental blood vessels. In males, only meiosis and sperm differentiation occur while the cells are free in the coelom. In females, oocytes are only released into the coelom briefly, after vitellogenesis has been completed. H. imbricata thus differs from most polychaete species so far described — where in males the spermatogonia divide mitotically to form rosettes after they have been released into the coelom, and in females the whole of vitellogenesis occurs after release of oocytes into the coelom. The oocytes of H. imbricata enter the first metaphase of meiosis before they are shed at spawning. The elongated head of the sperm in H. imbricata is atypical of polychaetes in general.     

Functional morphology of the gonads of the articulate brachiopodTerebratulina retusa

The reproductive anatomy, and ultrastructural features of the gonads of the articulate brachiopodTerebratulina retusa (Linnaeus), are documented based on collections made between October 1985 and October 1986 from the Firth of Lorn, west coast of Scotland. This species is dioecious, and maturity is achieved in both sexes at shell lengths greater than ~5.5 mm. There is no obvious external sexual dimorphism except for slight differences in the coloration of the gonads; testes are white/cream, ovaries are yellow/orange. The gonads occur as four palmate lobes, a pair in each valve. Gonads are formed within a mantle sinus (vascula genitalia), which is an anterior extension of the coelom, that opens posteriorly into the visceral cavity and to the exterior via a pair of metanephridia. The latter serve as gonoducts during spawning. Gametes are borne on genital lamellae formed from a reticulate lattice of connective tissue. The lamellae are an extension of the ileoparietal band and are fused along one margin to the inner mantle membrane. Developing oocytes are closely affixed to the genital lamellae and originate from a pool of proliferating germ cells at its base. Vitellogenic oocytes that are at an advanced stage are released from the genital lamellae, but are retained within thevascula genitalia. Liberated oocytes continue to accumulate yolk and eventually occlude thevascula genitalia, before being spawned. Coelomocytes were identified within the gonads. In spent females these cells appear to be phagocytic and involved in the resorption of necrotic material, while in the male they may serve as nutritive cells.     

Defenses and refuges: alternative mechanisms of coexistence between a predatory gastropod and its ascidian prey

Only five of the 14 species of solitary ascidians in the San Juan Islands, Washington, USA commonly co-occur with an abundant predator of the rocky subtidal, the gastropod Fusitriton oregonensis. None of the common subtidal species is defended by vanadium or sulfuric acid; concentrations of these substances are highest in species that are eaten readily by F. oregonensis and are uncommon in the rocky subtidal. Experimental manipulations indicate that Halocynthia igaboja are protected by stiff spines of the tunic. The defense mechanism of Pyura haustor consists of a tough, leathery tunic with inorganic inclusions, and microscopic spines around the siphons. Boltenia villosa and Styela gibbsii are eaten by snails in the laboratory, but live in areas where the predator is abundant. Both find refuge as epizooites on P. haustor and H. igaboja. The mechanisms by which Cnemidocarpa finmarkiensis persists in the presence of F. oregonensis is unknown.     

On the use of nearest neighbor contingency tables for testing spatial segregation

For two or more classes (or types) of points, nearest neighbor contingency tables (NNCTs) are constructed using nearest neighbor (NN) frequencies and are used in testing spatial segregation of the classes. Pielou’s test of independence, Dixon’s cell-specific, class-specific, and overall tests are the tests based on NNCTs (i.e., they are NNCT-tests). These tests are designed and intended for use under the null pattern of random labeling (RL) of completely mapped data. However, it has been shown that Pielou’s test is not appropriate for testing segregation against the RL pattern while Dixon’s tests are. In this article, we compare Pielou’s and Dixon’s NNCT-tests; introduce the one-sided versions of Pielou’s test; extend the use of NNCT-tests for testing complete spatial randomness (CSR) of points from two or more classes (which is called CSR independence, henceforth). We assess the finite sample performance of the tests by an extensive Monte Carlo simulation study and demonstrate that Dixon’s tests are also appropriate for testing CSR independence; but Pielou’s test and the corresponding one-sided versions are liberal for testing CSR independence or RL. Furthermore, we show that Pielou’s tests are only appropriate when the NNCT is based on a random sample of (base, NN) pairs. We also prove the consistency of the tests under their appropriate null hypotheses. Moreover, we investigate the edge (or boundary) effects on the NNCT-tests and compare the buffer zone and toroidal edge correction methods for these tests. We illustrate the tests on a real life and an artificial data set.     

How do slugs cope with toxic alkaloids?

Summary. Arion lusitanicus and other slugs are able to feed on a variety of plants, even those containing toxic secondary metabolites, such as alkaloids. Alkaloids, like sparteine, lupanine, quinidine and atropine are avoided in no-choice feeding experiments only when they are present in concentrations above 1 mg/g food pellet. Alkaloids (sparteine, lupanine, cytisine, quinidine, atropine, senecionine, eserine, and harmaline) are toxic to Arion lusitanicus when injected. LD₅₀ values are 10 to 20 fold higher than in vertebrates indicating that slugs have a high tolerance towards food toxins. The tolerance is higher in young animals than in adult slugs. Injected alkaloids are rapidly detoxified within 72 h. Tolerance and detoxification can be induced by feeding slugs on non-lethal doses of lupin alkaloids. Using isolated microsomal preparations from the digestive gland, active detoxification was observed in vitro. Evidence is presented that cytochrome p450 plays an important role in detoxification of the applied alkaloids. A powerful and inducible detoxification systems appears to be the main mechanism that allows slugs to feed on plants rich in secondary metabolites (when no other food is available), that are usually avoided by other herbivores.     

Water pollutant monitoring with aquatic bryophytes: a review

Bryophytes are non-vascular plants with large biomass and high production level in freshwaters. Aquatic bryophytes are used to assess the ecological status. They are a stress-tolerant group, and many species have a wide trophic range. Aquatic bryophytes are used as indicators by the presence or absence of a pollutant, or as monitors to measure pollutant concentrations. Here, we review major advances in bryomonitoring from a range of countries, mainly in Europe. Monitored elements include Ba, Cd, Cr, Cu, Co, Ni, Pb, Zn, Fe, Mn, V, ¹³⁷Cs, ¹³⁴Cs, ²³⁵U, ²³⁶Ra, ²³²Th and ⁴⁰K. We illustrate the advantages of low-cost methods for monitoring water quality. Biomonitoring includes (1) passive observation and analysis of native bryophytes and (2) active biomonitoring based on species transplantation for a fixed exposure period. Two widespread northern hemisphere aquatic mosses, Fontinalis antipyretica and Platyhypnidium riparioides, are the most common biomonitors.     

Analyzing and quantitatively evaluating the organic matter source at different ecologic zones of tidal salt marsh, North Jiangsu Province, China

In order to explore the effect of different ecological zones and their above plants in the organic matter cycling of the whole tidal salt marsh, indicators such as total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ¹³C and δ¹⁵N of surface, core sediments, and plants of tidal salt marshes in North Jiangsu Province are analyzed. Subsequently, distribution regularities of these measurement indicators are discussed, and the biogeochemistry processes between sediments and plants are also analyzed. Lastly, the organic matter sources of different ecologic zones in tidal salt marsh are evaluated, and the organic matter accumulations in different ecologic zones induced by their plants are also compared. These results indicate that TOC, TN, C/N ratio and δ¹³C showed obvious zonal distribution. The organic matter sources are dominated by marine input in the silt flat, artemisia schrenkiana flat, and the transition zone between silt and spartina alterniflora flat, and are controlled by terrigenous input in spartina alterniflora flat. Spartina alterniflora plays an important role in the accumulation of organic matter in the whole tidal salt marshes ecosystem. In the study area, the annually increased TOC, organic matter and TN in the spartina alterniflora, artemisia schrenkiana and reed flats reach 6,451, 12,043 and 536 t, respectively. The amount of TOC, organic matter and TN accumulated in the spartina alterniflora flat is more than that in other ecological zones, which shows that the spartina alterniflora flat exert a non-replaceable effect on the material cycle and exchange in the whole tidal salt marshes ecosystem.     

Bacteria on the surface of crustose coralline algae induce metamorphosis of the crown-of-thorns starfish Acanthaster planci

The crustose coralline alga Lithothamnium pseudosorum induces high rates of settlement and metamorphosis of larvae of the coral-eating crown-of-thorns starfish (Acanthaster planci). In cases where crustose coralline algae (CCA) induce metamorphosis of marine invertebrate larvae it is normally assumed that the inductive molecules are produced by the alga, but an alternative is that they originate from bacteria on the plant surface. Bioassays using shards of L. pseudosorum treated with several antibiotics, whereby some shards were reinfected with bacteria from the alga, showed that if bacteria populations are depleted then settlement and metamorphosis of larvae of A. planci are inhibited. This demonstrates that bacteria are necessary for induction and suggests that morphogenic substances are produced by bacteria on the surface of the alga and not directly by the alga itself. However, surface bacteria are not inductive if they are isolated from soluble algal compounds, suggesting either that they require a substrate from the alga to produce the inductive agents or, alternatively but less likely, that compounds from both the alga and bacteria are required. There is no evidence that inductive compounds derive from the alga, since algal cell debris and soluble extracts prepared from the alga do not induce metamorphosis of A. planci. This is the first time that induction of metamorphosis in a marine invertebrate by CCA has been shown to be mediated by bacteria associated with the alga.     

Evolution of reproductive features and larval development in the genus Amphiglena (Polychaeta: Sabellidae)

Larval development in Amphiglena mediterranea is direct in the parental tube, and larvae crawl away as young juveniles with a radiolar crown capable of feeding. The non-feeding larvae of A. nathae are initially brooded in the parental tube, and then have a swimming phase before settling and developing a radiolar crown. Developmental data and reproductive features such as sperm structure are combined with other morphological data for an assessment of the cladistic relationships of the species in the genus Amphiglena. Two species of Laonome are included as part of the ingroup. Six genera, representing a sister group to the Laonome/Amphiglena clade, are used as an outgroup. Two most-parsimonious cladograms were found, and the evolution of reproductive features are discussed. The monophyly of Amphiglena is indicated by features previously identified, as well as two features based on sperm morphology. At present a plesiomorphic larval form cannot be identified for the genus Amphiglena. Received: 16 June 1997 / Accepted: 29 January 1998     

The occurrence and need for conservation of metallophytes on mine wastes in Europe

Metalliferous substrates are important in the distribution of various plants such asArmeria maritima, Minuartia verna, Thlaspi alpestre, Silene maritima andCochlearia officinalis, in parts of the United Kingdom. Metalliferous substrates are similarly important for a slightly different assemblage of metallophytes in the Aachen-Liège orefield in Belgium and Germany. The significance of metalliferous substrates in the distribution of the metallophytes varies from orefield to orefield and this is investigated. Certain sites, by virtue of their environmental and species diversity, are outstanding as habitats for the metallophytes and some of these are described. Observations on the importance and problems of the conservation of the metallophyte habitats are included.