A review of the biology, ecology and potential use of the common ragworm Hediste diversicolor (O.F. Müller) (Annelida: Polychaeta)

The common ragworm Hediste diversicolor inhabits the shallow marine and brackish waters in the North Temperate Zone of the Atlantic. This infaunal species builds U or Y-shaped burrows in the soft sediments. H. diversicolor is gonochoristic and remains atokous throughout its life. Due to the facility of harvesting of individuals by hand and their maintenance, this species represents a good biological material for experimental studies. In consequence, the common ragworm served as a model for endocrine control of reproduction in Polychaeta and played a fundamental role in the study of immune defence in Polychaeta.Life history characteristics (longevity, spawning season, feeding tactics and growth) and population dynamics (sex ratio, density and biomass) vary greatly according to geographical location of the populations. In addition, inter-population morphological, biochemical and physiological differences have been noticed in individuals from different areas and different environmental conditions in the same areas and could be related to the limited dispersal capacity of the species. H. diversicolor interacts with its environment. The construction of burrows by individuals increases the sediment–water interface. When they ventilate their burrows, individuals verticalize oxic zones into the sediment and promote microbial and meiofaunal growth alongside their burrows. Moreover, the common ragworm is a species of commercial interest because of its use as bait in recreational fishing and as food in aquaculture. In order to alleviate environmental pressure caused by excessive demand over optimal sustainable yield of bait fisheries, intensive aquaculture has been proposed. The common ragworm could be also used as biomonitor of pollution in estuarine ecosystems.     

Immunohistochemical demonstration of a CCK-like peptide in the nervous system of a marine annelid worm,Nereis diversicolor O.F. Müller

Summary Perikarya and nerve fibers containing a substance immunologically related to CCK-8 were detected in the nervous system of Nereis, a marine annelid worm. The most noteworthy immunostaining was seen in cell bodies, localized at the periphery of the brain, within nuclei 5, 6, 7, 9, 10, 13, 14, 15, 17, 20, 23–24. Immunoreactive fibers were also found in the neuropile without any particular grouping. Numerous other positive perikarya occur in the medio-ventral portion of the ventral nerve cord, and in the ventral and dorsal parts of the suboesophageal ganglion. In addition to the cell bodies in the cerebral external layer, immunoreactive axons were abundantly observed in the connectives between the ganglia. Moreover, our results demonstrate CCK-like staining in neurons showing variations in size and shape, and in affinity for paraldehyde fuchsin. The present results support the hypothesis that this peptide may exert a role as neurotransmitter or neuromodulator in annelids.     

Effects of tissue extract of adults on metamorphosis in Ascidia mentula O.F. Müller and Ascidiella scabra (O.F. Müller)

Unhatched, but fully developed larvae of two solitary ascidians Ascidia mentula O.F. Müller and Ascidiella scabra (O.F. Müller) were incubated in a variety of adult tissue extracts, which an earlier study had shown to accelerate metamorphosis. Our study confirmed this observation and showed, furthermore, that tissue extracts induce tail resorption in unhatched larvae of Ascidiella. For both species, the most active induction of metamorphosis was obtained with tunic tissue extracts. The results indicate that chemical stimulation without the presence of tactile cues may initiate metamorphosis. We suggest that the ability of tunic extracts to induce metamorphosis may explain juvenile establishment on adult ascidians and their aggregated distribution found in nature.     

Smelling Danger – Alarm Cue Responses in the Polychaete Nereis (Hediste) diversicolor (Müller, 1776) to Potential Fish Predation

The harbour ragworm, Nereis (Hediste) diversicolor is a common intertidal marine polychaete that lives in burrows from which it has to partially emerge in order to forage. In doing so, it is exposed to a variety of predators. One way in which predation risk can be minimised is through chemical detection from within the relative safety of the burrows. Using CCTV and motion capture software, we show that H. diversicolor is able to detect chemical cues associated with the presence of juvenile flounder (Platichthys flesus). Number of emergences, emergence duration and distance from burrow entrance are all significantly reduced during exposure to flounder conditioned seawater and flounder mucous spiked seawater above a threshold with no evidence of behavioural habituation. Mucous from bottom-dwelling juvenile plaice (Pleuronectes platessa) and pelagic adult herring (Clupea harengus) elicit similar responses, suggesting that the behavioural reactions are species independent. The data implies that H. diversicolor must have well developed chemosensory mechanisms for predator detection and is consequently able to effectively minimize risk.     

Versuche über die Phototaxis von Nereïs diversicolor O. F. Müller

Ohne Zusammenfassung     

The reproductive morphology of Dumontia incrassata (O. F. Müller) Lamouroux

The reproductive morphology of Dumontia incrassata (O. F. Müller) Lamouroux is described from New Hampshire, U.S.A. populations. Mature carpogonial and auxiliary branches are usually 5 and 6 celled, respectively, but both may range from 4 to 9 cells. Auxiliary branches are more numerous than carpogonial branches; however, the ratio of carpogonial to auxiliary branches increases towards the apex of the frond. A linear relationship exists between the position of the generative auxiliary cell and the number of cells in the auxiliary branches. In most cases the third cell from the top of the auxiliary branch becomes the generative auxiliary cell. The probabilities for different positions of the generative auxiliary cells are summarized. During spermatangial development, four mother cells are initially produced per cortical cell initial; subsequently, successive spermatangia are cut off obliquely and on opposite sides of each mother cell. Monoecious asexual plants of D. incrassata are described, as well as an irregular tetraspore development.Scientific Contribution Number from the New Hampshire Agriculture Experiment Station; also issued as contribution No. 81 of the Jackson Estuarine LaboratoryScientific Contribution Number from the New Hampshire Agriculture Experiment Station; also issued as contribution No. 81 of the Jackson Estuarine Laboratory     

Distribution pattern of the dinoflagellateCeratium hirundinella (O. F. Müller) Bergh in a reservoir

Horizontal distribution of the dinoflagellateCeratium hirundinella (O. F. Müller) Bergh in the Ishitegawa Reservoir, Ehime Prefecture, Japan, was investigated. Water quality was also surveyed. It was observed that the population ofC. hirundinella exponentially decreased in number from the head of the reservoir to the dam site. Further investigation proved thatC. hirundinella initiated growth at the head of the reservoir, and later gradually expanded downstream. It was found during the period of increase in water temperature that the cell density ofC. hirundinella at the uppermost station exponentially increased.     

Possible sites of ultrafiltration in Tubifex tubifex Müller (Annelida,Oligochaeta)

Summary The endothelia of Tubifex tubifex Müller consist of myoendothelial cells, chloragocytes, or podocytes. The latter seem to occur only as windows on the ventral vessel which has an endothelium of myoendothelial cells elsewhere. The podocytes are large cells, with several processes on the inner side which ramify into several pedicels. These are aligned upon the outside of the basement membrane which lines the inside of the endothelium. The gaps between adjacent pedicels are about 40 nm wide. In capillaries fenestrated endothelia occur with irregular spacings measuring up to 0.4–1 m. A diaphragm in podocytes or capillary fenestrations do not seem to exist. The basement membrane is the only continuous layer lining the blood vessels and capillaries of Tubifex with a rather uniform diameter in the range of 50 nm. It is the only permeability barrier between blood and coelomic fluid.     

Observations on the clypeasteroid Echinocyamus pusillus (O. F. Müller)

The tiny echinoid Echinocyamus pusillus (O. F. Müller) is equipped with specialized external structures that suit it for a wide variety of environments. Special features include the ability to burrow in sediments of fine sand to shell gravel and to climb vertically.Specimens dredged off the west coast of Scotland were observed in aquaria and with the SEM. E. pusillus is characterized by three kinds of spines, and by two of pedicellariae. In contrast to sand dollars, the spines play a passive rôle in the feeding and burrowing operation, probably retaining a defensive nature as in the regular urchins. It is the podia that are chiefly involved in climbing, burrowing, righting, and probably feeding. Surface ciliary currents transport particles, but not to the mouth; they may have a respiratory or cleansing function. Experimental animals did not burrow in either very fine or very coarse sand, probably because a certain relationship exists between particle weight and podia size.E. pusillus shares behavioural and structural characteristics with regular and irregular urchins. It is not a true sand dollar, but may illustrate an evolutionary stage towards such a form.     

Population dynamics and estimation of production in Bosmina longirostris (O. F. Müller) in the River Danube (Danubialia Hungarica,CVIII)

Analysis of the population dynamics of Bosmina longirostris (O. F. Müller) was carried out in the River Danube in the years 1981 and 1982. An estimation method of secondary production elaborated far standing waters was adapted to river conditions. In the River Danube, compared to lakes, standing crop and production values were smaller, while fecundity, P/B values were larger and turnover time was shorter. Possible reasons for this are discussed.     

The morphology and fine structure of the colourless colonial flagellate Anthophysa vegetans (O. F. Müller) Stein

A strain of Anthophysa vegetans (O. F. Müller) Stein (Chrysophyceae or Chrysomonadida) was grown in culture and examined in detail by light and electron microscopy. It was shown to be a typical, though apochlorotic, member of its class; features of interest include a well-developed leucoplast and a starch-like reserve product. Aspects of the largely inorganic stalk are also discussed.     

On barriers to hybridization between Strongylocentrotus droebachiensis (O.F. Müller) and S. Pallidus (G.O. Sars)

Strongylocentrotus droebachiensis (O. F. Müller) and Strongylocentrotus pallidus (G. O. Sars) occur together over much of their ranges in both the Atlantic and Pacific Oceans and remain distinct species, but no strong barrier to genetic exchange has been found in a study in the San Juan Islands. Co-occurrence of embryos of both species in the plankton indicates similar times of spawning. Ova of S. droebachiensis are fertilized by sperm of S. pallidus but the reciprocal cross gives a percent fertilization near zero. Hybrids of both crosses are viable with pigmentation resembling S. pallidus in the larval stage and S. droebachiensis in the adult stage. Ova of first generation female hybrids are more readily fertilized by sperm of S. pallidus, so that gene flow through female hybrids is more likely to be from S. droebachiensis to S. pallidus than the reverse. Male hybrids were not tested. S. droebachiensis and S. pallidus from deeper waters have lower fecundity than shallow water S. droebachiensis, which suggests that in the deeper waters individuals are food limited. The hypothesis that S. pallidus uses the sterile male technique to reduce reproductive output of S. droebachiensis is considered and rejected.     

General morphology and ultrastructure of the radula of Testudinalia testudinalis (O. F. Müller, 1776) (Patellogastropoda,Gastropoda)

The radular morphology of the patellid species Testudinalia testudinalis (O. F. Müller, 1776) from the White Sea was studied using light, electron, and confocal microscopy. The radula is of the docoglossan type with four teeth per row and consisting of six zones. We characterize teeth formation in T. testidinalis as follows: one tooth is formed by numerous and extremely narrow odontoblasts through apocrine secretion; this initially formed tooth consists of numerous vesicles; the synthetic apparatus of the odontoblasts is localized in the apical and central parts of the cells throughout the cytoplasm and is penetrated by microtubules which are involved in the transport of the synthesized products to the apical part of the odontoblast; the newly formed teeth consist of unpolymerized chitin. Mitotic activity is located in the lateral parts of the formation zone. The first four rows contain an irregular arrangement of teeth, but the radular teeth are regularly arranged after the fifth row. The irregularly arranged teeth early on could be a consequence of the asynchronous formation of teeth and the distance between the odontoblasts and the membranoblasts. The morphological data obtained significantly expands our knowledge of the morphological diversity of the radula formation in Gastropoda.     

Physiological adaptations in the survival of rotifers (Brachionus plicatilis,O. F. Müller) at low temperatures

The biology of the rotifer Brachionus plicatilis has been studied extensively in recent years, due to its importance in aquaculture. Today, the culture of several marine fish species relies completely on the daily production of live rotifers.In the present paper we explore the conditions that facilitate maintaining live rotifers for extensive periods at low temperatures. In addition to its possible contribution in providing reserve stocks for commercial application, these studies may be of ecological importance. They could explain some of the physiological adaptive mechanisms that are involved in the survival of rotifers under adverse environmental conditions.Experimental results showed relatively high survival rates (82–85%) in rotifers that were cultured at 25 °C and exposed later to -1 °C for 12–14 days. During this period, rotifers were kept without food and their media were not changed. The survival was found to depend on the rotifer culture conditions, prior to exposure to -1 °C. These included the type of food fed to rotifers (yeast or algae), the salinity in which they were cultured, and an essential acclimation period of 2–6 day at 4 °C or 10 °C. The acclimation period was associated with the synthesis of at least one specific protein and accumulation of lipids. Profiles of protein synthesis in rotifers incubated at 10 °C revealed a 94 kD protein, which did not appear in rotifers cultured at 25 or 37 °C. Immunoisolation, using a polyclonal antibody that was prepared against HSP60, revealed that this protein was synthesized in rotifers kept at 10, 25 or 37 °C. However, this antibody did not react with the 94 kD peptide.In addition, rotifers kept at 10 °C accumulated substantial amounts of lipids, including eicosapentaenoic acid (EPA), which is found in the algae fed to them. These results support the hypothesis of specific adaptations to survival at low temperatures during an acclimation period.