Opisthobranch Mollusc Research Articles

Diets of Dunlin Calidris alpina and Grey PloverPluvialis squatarolaon the Wash as determined by dropping analysis

Droppings of Dunlin Calidris alpina and Grey Plover Pluvialis squatarola were collected on the Wash, south-east England, and examined for remains of prey species taken. Dropping analysis was found to be useful in describing the diet of these two waders. In addition to confirming known prey species, previously unrecorded prey were discovered: in the case of Dunlin, worms -of the families Spionidae and Phyllodocidae and in the case of Grey Plover, the amphipod crustacean Corophium volutator. Both Dunlin and Grey Plover were found to be taking the opisthobranch mollusc Retusa obtusa¸, a prey species which has not been recorded in the diet of waders before.

Cell-cell interactions determine the dorsoventral axis in embryos of an equally cleaving opisthobranch mollusc.

Dorsoventral polarity in molluscan embryos can arise by two distinct mechanisms, where the mechanism employed is strongly correlated with the cleavage pattern of the early embryo. In species with unequal cleavage, the dorsal lineage, or "D quadrant", is determined in a cell-autonomous manner by the inheritance of cytoplasmic determinants. However, in gastropod molluscs with equal cleavage, cell-cell interactions are required to specify the fate of the dorsal blastomere. During the fifth cleavage interval in equally cleaving embryos, one of the vegetal macromeres makes exclusive contacts with the animal micromeres, and this macromere will give rise to the mesodermal precursor cell at the next division, thereby identifying the dorsal quadrant. This study examines D-quadrant determination in an equally cleaving species from a group of previously uninvestigated gastropods, the subclass Opisthobranchia. Blastomere ablation experiments were performed on embryos of Haminoea callidegenita to (i) determine the developmental potential of macromeres before and after fifth cleavage, and (ii) examine the role of micromere-macromere interactions in the establishment of bilateral symmetry. The results suggest that the macromeres are developmentally equivalent prior to fifth cleavage, but become nonequivalent soon afterward. The dorsoventral axis corresponds to the displacement of the micromeres over one macromere early in the fifth cleavage interval. This unusual cellular topology is hypothesized to result from constraints imposed on micromere-macromere interactions in an embryo that develops from a large egg and forms a stereoblastula (no cleavage cavity). Ablation of the entire first quarter of micromeres results in embryos which remain radially symmetrical in the vegetal hemisphere, indicating that micromere-macromere interactions are required for the elaboration of bilateral symmetry properties. Therefore, inductive interactions between cells may represent a general strategy for dorsoventral axis determination in equally cleaving gastropods.

Umbraculumin-B, an unusual 3-hydroxybutyric acid ester from the opisthobranch mollusc umbraculum mediterraneum

The structure and stereochemistry of Umbraculumin-B, a metabolite isolated from the skin extracts of the opisthobranch mollusc Umbraculum mediterraneum, have been established by spectroscopic and chemical methods.

Evidence for chaos in spike trains of neurons that generate rhythmic motor patterns

The findings presented here of work on the opisthobranch mollusc Pleurobranchaea californica indicate that some of the variability that has been observed in the activity of neurons during patterned motor activity may be attributable to low-dimensional chaos. We obtained long trains of action potentials (spikes) from these neurons, scanned them using adjacent temporal windows having equal widths, and converted the counts into frequency time series. These series were passed through a low-pass filter and detrended when necessary. The resulting time series gave a view of the envelopes of high-frequency bursts of spikes relating to the repetitive motor activity rather than of the intervals between spikes. Where applicable, we also compared analyses of smoothed data with the unprocessed spike intervals and found similar results for each type of time series. Autocorrelation functions of the processed data quickly decreased to zero, indicating that the long-term evolution of the time series could not be predicted from information at some given time. The first zero crossing of the autocorrelation function was used to define the lag for mapping the series into multidimensional phase space. These constructions were then used to examine the dynamics of the motor patterns directly from the state parameters of the time series, 1-D maps obtained from Poincare slices of 2-D phase portraits, principal Lyapunov exponents, and correlation dimensions all indicated that the activity may be attributable to low-dimensional chaos. The present findings are similar to those of previous work in which equal-interval time series were obtained by interpolation of the unequal-interval spike trains. We discuss the implications of chaos and the difficulties in the application of extant dynamical tools to spike trains. An accompanying paper inquires into the ability of neural networks to read and transmit chaotic activity.

CCK-8 inhibits feeding-specific neurons in Navanax, an opisthobranch mollusc

Cholecystokinin has been implicated as a satiety factor in mammals because it inhibits feeding through peripheral and central mechanisms. The cellular mechanisms of the central actions of CCK have been difficult to study because of the complex circuitry of the mammalian brain. Navanax is an opisthobranch mollusc with a defined neural network for feeding behavior in which the central effects of CCK can be studied at the cellular level. Here we report the localization of CCK-immunoreactivity in neuronal cell bodies and varicose fibers in the buccal ganglion of Navanax and that CCK-8 inhibits buccal ganglion neurons selectively and at tenth picomolar concentrations: expansion motoneurons responsible for prey capture are strongly inhibited by CCK-8; circumferential motoneurons responsible for swallowing are weakly inhibited by CCK-8. A large cell, cell X, is described which is sensitive to very low doses of CCK-8. These data imply the existence of a CCK-like peptide with transmitter-like actions in the buccal ganglion of Navanax.

Two ichthyotoxic diacylglycerols from the opisthobranch mollusc [formula omitted][formula omitted

Two ichthyotoxic diacylglycerols, umbraculumin-A ( 1 ) and -C ( 2 ), have been isolated from theskin of the opisthobranch mollusc Umbraculum mediterraneum and their structures determined by spectroscopic means.

New propionate-derived metabolites from Aglaja depicta and from its prey Bulla striata (opisthobranch mollusks)

New propionate-derived metabolites from Aglaja depicta and from its prey Bulla striata (opisthobranch mollusks)

Simultaneous optical recording of activity from many neurons during feeding in Navanax

Optical methods for monitoring changes in membrane potential have been used to measure action potential activity in the buccal ganglion of an opisthobranch mollusc, Navanax inermis, while the animal was feeding. During feeding activity was detected in 10-15% of the approximately 200 neurons present in the ganglion. Control experiments carried out to determine the completeness of the optical recording showed that activity in at least 70% of the neurons could be detected. Thus, in certain invertebrate ganglia, it is possible to make a reasonably complete recording of the neuron activity responsible for generating relatively complex behaviors.

Spinning embryos enhance diffusion through gelatinous egg masses

Heat transfer rate was used as an analog in determining the effect of embryonic movement on diffusion rates through gelatinous egg masses of the opisthobranch mollusc Haminoea sp. Egg masses containing spinning embryos had thermal conductivities (and, by analogy, diffusion rates) at least 7.6% greater than egg masses containing non-spinning embryos. Spinning may thus provide a mechanism that increases the rates of diffusion-limited processes in the developing embryo.

Ultrastructural study of oogenesis and yolk formation in an opisthobranch mollusc, Runcina

Runcina is a hermaphroditic opisthobranch mollusc of small size. It produces large eggs, rich in yolk substances, and it is thus ideal for studying the mechanisms of vitellogenesis. The rough endoplasmic reticulum and the Golgi apparatus appear to be involved in early build up of yolk precursors. Endocytotic vesicles carrying yolk proteins, taken up from the haemolymph, dominate yolk formation at a later stage. The findings presented in this study enhance the proposition of a dual pathway of auto- and heterosynthesis in yolk formation. It is not found that the yolk bodies in Runcina acquire lysosomal enzymes in order to digest the perivitelline fluid, as has been described for some pulmonates. The importance of the role played by the follicle cells in oocyte development is discussed.

Co-activation, cell assemblies and learning

Donald O. Hebb's Organization of Behavior (1949) 1 set an agenda that continues to guide research in neuroscience. In it, Hebb sought to provide a neuropsychological framework to account for the complex phenomena of perception, ideation, attention, and, in particular, the formation of learned associations. Hebb drew on an extensive body of anatomical, physiological and psychological evidence, much of it generated by his own contributions, to argue that the substrate of associations lay in activity-dependent changes at synapses. He postulated that repeated co-activity of synaptically connected cells leads to a lasting cellular change that strengthens thier connection. This process was envisioned to lead the slow development of diffuse ‘cell assemblies’ in the cortex, thalamus and basal ganglia that encoded associations and were thus able to modify behavior 1. This provocative hypothesis presented in 1949 continues to stimulate research in 1985: a recent investigation by Carew, Hawkins, Abrams and Kandel 2 examines the role of co-activity of pre-and post-synaptic neurons in classical conditioning in the simple nervous system of the opisthobranch mollusc, Aplysia californica.

Regional specializations in the eye of Aplysia, a neuronal circadian oscillator.

The eye of the opisthobranch mollusc, Aplysia californica, contains a neuronal circadian oscillator system as well as a photoreceptor system. The retina contains five classes of receptors, several of which are described for the first time in this paper, and two types of neurons. The most conspicuous photoreceptor has long microvilli and is densely packed with small vesicles. The other four receptor types bear both microvilli and cilia and lack densely packed vesicles. Because of their small size, these four receptors occupy only a small fraction of the retinal area, but numerically they account for about half of the receptors. There are marked differences between the dorsal and ventral portions of the eye of Aplysia. The optic nerve head and associated bundles of axons within the retina form a boundary between two anatomically distinct regions of the eye. The microvillous photoreceptor and one of the receptors bearing both microvilli and cilia are found throughout the eye. The other three receptor types are restricted to the region ventral to the optic nerve head. One type of neuron, which has been shown in other studies to produce compound action potentials whose frequency varies with a circadian rhythm, is also found only ventral to the optic nerve head and associated axon bundles. There are also marked regional variations in cellular dimensions. The rhabdom originating from the microvillous photoreceptors is thickest in the dorsal and central retina, and the cross-sectional areas of these photoreceptors are largest dorsally. The pigmented layer is also much thicker in the dorsal retina. No other molluscan eye has been reported to have as many receptor types as Aplysia, nor has restriction of a receptor or neuronal type to a limited area been described. Regional variations in cellular dimensions have been reported previously primarily in the advanced cephalopod eyes. The significance of these unusual features is discussed in relation to both the visual properties of the eye and the circadian oscillator it contains.

Parallel Evolution in Opisthobranch Gastropods and its Implications for Phylogenetic Methodology

-Parallel as exemplified by data on opisthobranch mollusks (a group in which snails have repeatedly evolved into slugs), often exceeds divergent evolution. A similar level of parallelism has been described in an array of other organisms. This fact presents serious challenge to those systematists who claim that cladogram with minimal number of steps represents most parsimonious and most likely scenario of genealogical relationship. When rampant parallelism is present, pattern cladism or other congruence networks which rely solely on ingroup comparison of characters are unsuccessful in resolving the problem. We suggest that emphasis on unique innovation and divergent apomorphy presents fruitful and scientifically consistent alternative to this dilemma. We contend that cladists have drastically altered the meaning of several terms-including parallel evolution, parsimony, and a priori-to suit their own methodological and philosophical paradigm. These modifications reduce the testability of their hypotheses and, therefore, the scientific credibility of their methods. The construction of genealogy based on shared-derived features, which is independent of theoretical basis, represents resurfacing of typological thinking which has little value in explaining or even depicting the patterns of diversity of life. [Parallel evolution; parsimony; methodology; opisthobranch gastropods.] Phylogenetics is the sun around which revolves, carrying with it the whole of comparative biology. This was one of Darwin's most important contributions. Our classifications will come to be, as far as they can be made so, genealogies (Darwin, 1859:486). What may be called classical phylogenetics was founded by Darwin and has continued as part of ever since. However, the sunlight of genealogy has often been obscured by the umbrage of typology, often motivated by efforts to discredit evolutionary biology in general. Repeatedly, it has been necessary to return to fundamentals and devise methodologies adequate to the task. A major figure in such endeavors was Hennig (1950, 1966), whose phylogenetic systematics has been the inspiration for the so-called cladist tradition. The result has been continued polarization among factions; legitimate methodologies, long accepted and used by competent evolutionary biologists, have been treated as if they did not exist. We believe that it is time for these issues to be more fully examined. We contend that many cladists have systematically dismissed some major operational and philosophical difficulties with their methods and ignored some alternative or supplementary techniques which might achieve better results. We find much of what cladists say perfectly acceptable. There is no question that one of the goals of is to infer genealogical relationships. There being just one historical reality, there is one (and only one) true tree for any group of organisms. Employing innovations or apomorphies to infer lineages is, or should be, operationally routine. Such matters as whether to allow paraphyletic taxa are not the bones of contention they might seem, being matters of formal classification, not history proper. The thesis that species and other taxa are inAdividuals (Ghiselin, 1966a, 1969a, 1974a, 1981) has been accepted by many cladists (e.g., Eldredge and Cracraft, 1980;

Functional adaptations of the digestive system of the carnivorous mollusc Pleurobranchaea californica MacFarland, 1966.

The opisthobranch mollusc Pleurobranchaea californica feeds on whole organisms and the functional morphology of the digestive system reflects this behavior. By a rhythmic behavior involving well-developed extrinsic buccal muscles and hemocoelic fluid, the buccal mass is protracted to the tip of the everted oral tube. Here a series of repeated protractions and retractions of the intrinsic buccal muscles associated with the flat radular ribbon and jaws draws the prey into the buccal cavity and conveys it to the dorsal esophagus, where by peristaltic action it is passed to the expansible crop for storage. Prey entering the buccal cavity is mixed with acid from a large single gland and secretion from the paired salivary glands. Prey is retained in the crop over long periods of time while it is slowly broken down and passed via the stomach into the digestive glands. Special modifications that allow flexibility of the digestive organs include elongated salivary gland ducts with propulsive bulbs, long flexible nerve cords connecting the ganglia, a long, large muscular duct for storage of the acid secretion, large jaws for muscle attachment and grasping the prey, and a broad radular ribbon with many teeth that acts as a conveyor belt to move food. Additional modifications for handling whole prey include a buccal membrane that aids in maintaining hemocoelic fluid pressure, the extensive acid gland for immobilization of prey, and the expansible crop for storage of food.

Some In Vivo and In Vitro Characteristics of Aplysia Californica Haemolymph*

ABSTRACT The nervous system of the opisthobranch mollusc, Aplysia californica Cooper has been extensively studied and a great deal is known about the electrophysiological properties of a number of identifiable neurones (see Kandel, 1976, 1979). A variety of synaptic and electrical connections have been mapped, permitting identification of the mode in which nervous control is exerted over certain motor functions. Substantially less is known regarding other physiological systems of Aplysia (Kandel, 1979), particularly the respiratory system, and this limits the description of how nervous control is affected by internal physiological state. Chalazonitis & Nahas (1965) reported data for haemolymph pH, CO2 tension and O2 tension in the related species, Aplysia fasciata, and Bevelaqua et al. (1975) identified the respiratory pigment, haemocyanin, in the haemolymph of A. californica. However, there has been no detailed study of in vivo oxygen levels or acid-base status of A. californica. Neither are there any data for the in vitro properties of A. californica haemolymph, such as oxygen carrying capacity, oxygen affinity or buffering properties. Such data are of particular importance in A. californica, for two reasons. Firstly, motor function, such as the often-studied gill withdrawal reflex, may be directly influenced by factors such as pH, or as are the respiratory performances of other marine invertebrates (Mangum & Burnett, 1975; McMahon & Wilkens, 1975; Bayne, 1976; Batterton & Cameron, 1978). Secondly, Chalazonitis (1974) has shown clearly that membrane potential, spike frequency and membrane resistance of many single cells in A. fasciata are directly affected by pH, and of the bathing fluid. Therefore, the present study was undertaken to describe some of the in vivo and in vitro properties of the haemolymph of A. californica with regards to acid-base status and oxygenation characteristics.

Undulating arrays of endoplasmic reticulum in the spermatids of an opisthobranch mollusc

Peculiar undulating cisternae of endoplasmic reticulum have been observed in the spermatids of the opisthobranch mollusc Spurilla neapolitana. Analysis of sections suggests that these arrays of ER might be a multilamellar structure consisting of paired cytomembranes molded into parallel, conical elevations with hexagonal bases. The structure is associated most frequently with the Golgi complex of the spermatid but its function is unknown. Other reports of similar arrays of ER in both plant and animal cells are discussed and compared with those of Spurilla spermatids.

Synaptic organization of expansion motoneurons of Navanax inermis

The opisthobranch mollusc, Navanax, feeds by rapid pharyngeal expansion that sucks in prey followed by peristaltic swallowing that moves prey into the esophagus. Several identifiable neurons on the ventral surface of the buccal ganglia control radial musculature within the pharyngeal wall, contraction of which leads to pharyngeal expansion. These are considered expansion motoneurons because their axons run into the muscle and twitches and EMGs occur one for one with action potentials. The motoneurons are electrotonically coupled. Electrotonic PSPs, the components of spread associated with impulses, can summate with subthreshold DC depolarizations to yield synchronous impulses in coupled cells. During a train of responses the later electrotonic PSPs can be facilitated because of increase in amplitude and duration of the presynaptic impulses. Expansion motoneurons are synaptically connected by two apparently interneuronal pathways: a low threshold pathway activated by subthreshold depolarization of the two largest expansion motoneurons (the G-cells) that inhibits the entire population, and a high threshold pathway that is activated by a train of G-cell impulses and produces largely excitatory PSPs in the smaller expansion motoneurons and an EPSP--IPSP sequence in the G-cells. Coupling among expansion motoneurons can be abolished by chemical inhibitory synaptic inputs that are activated by electrical stimulation of the pharyngeal nerve or tactile stimulation of the pharyngeal wall. This uncoupling phenomenon can be explained by a simple equivalent circuit in which inhibitory synapses along the coupling pathway short circuit electrotonic spread. Uncoupling can outlast the evoking stimulus by several seconds. During uncoupling the smaller expansion motoneurones can fire independently while the G-cell is inhibited, and impulses still propagate from somata to the periphery. The expansion motoneuron population receives excitatory input from the mechanoreceptors in protractor muscles. Mechanical stimulation of the pharyngeal wall activates primary sensory neurons in the buccal ganglia that fire during excitation and during inhibition and uncoupling of expansion motoneurons.

The ecology and anatomy of a new species of aeolid opisthobranch mollusc; a predator of the scleractinian coral Porites

A new species of aeolid opisthobranch (family Tergipedidae) is described from Tanzania. It lives and feeds on the scleractinian coral Porites somaliensis. Studies on its development show that it can reach sexual maturity three weeks after hatching. The larval stage is extremely abbreviated; the veliger settles ten minutes after hatching, and within ninety minutes of hatching has assumed a slug-like form.

Crispatone, a metabolite of the opisthobranch mollusc Tridachia crispata

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCrispatone, a metabolite of the opisthobranch mollusc Tridachia crispataChris Ireland, D. John Faulkner, Janet S. Finer, and Jon ClardyCite this: J. Am. Chem. Soc. 1979, 101, 5, 1275–1276Publication Date (Print):February 1, 1979Publication History Published online1 May 2002Published inissue 1 February 1979https://doi.org/10.1021/ja00499a037RIGHTS & PERMISSIONSArticle Views103Altmetric-Citations22LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (261 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Ultrastructural and physiological studies on the longitudinal body wall muscle of Dolabella auricularia. I. Mechanical response and ultrastructure.

The physiological properties of mechanical response and the ultrastructure in the longitudinal body wall muscle (LBWM) of the opisthobranch mollusc Dolabella auricularia were studied to obtain information about excitation-contraction coupling in somatic smooth muscles responsible for smooth and slow body movement of molluscans. The contracture tension produced by 400 mM K was not affected by Mn ions (5--10 mM) and low pH (up to 4.0), but was reduced by procaine (2 mM). The K-contracture tension was not readily eliminated in a Ca-free solution containing ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA). A large contracture tension was also produced by rapid cooling of the surrounding fluid from 20 degrees to 5 degrees--3 degrees C even when the preparation showed no mechanical response to 400 mM K after prolonged (more than 2 h) soaking in the Ca-free solution. These results indicate that the LBWM fibers contain a large amount of intracellularly stored Ca which can be effectively released by membrane depolarization. The fibers were connected with each other, forming the gap junctions, the desmosomes, and the intermediate junctions. The sarcoplasmic reticulum (SR) consisted of vesicular and tubular elements, and was mostly located near the fiber surface. The plasma membrane showed marked tubular invaginations of 600-800 A in diameter, with many branches (surface tubules), extending inwards for approximately 2 micron. These surface tubules were closely apposed to the SR, and the bridgelike structures analogous to those in the triadic junction of vertebrate skeletal muscle were observed in the space between the surface tubules and the SR. It is suggested that the influence of membrane depolarization is transmitted inwards along the surface tubules to cause the release of Ca from the SR.