Opisthobranch Mollusc Research Articles

Heterochronies in the formation of the nervous and digestive systems in early postlarval development of opisthobranch mollusks: Organization of major organ systems of the arctic dorid Cadlina laevis

For the first time using laser confocal microscopy and histochemical and immunocytochemical methods (detection of F-actine, catecholamines, acetylcholintransferase, substances of P and FM RFamide) in combination with classical histological methods and electron microscopy of total preparations, the general structure and regularities of formation of the main organs and the nervous, muscular, and digestive systems in early postlarval development (2 to 4 months) in the opistobranch mollusk Cadlina laevis were studied. Heterochronies manifested in positive allometry of the sensory organs, ganglia of the central nervous system, and the pharyngeal region of the digestive system in relation to general body sizes in juvenile individuals compared to adult animals were detected.

Holding On to a Shifting Substrate: Plasticity of Egg Mass Tethers and Tethering Forces in Soft Sediment for an Intertidal Gastropod

Staying attached at a favorable site can be a major challenge for organisms in flow. Meeting this challenge depends on properties of the attachment structure and substrate, the nature of fluid flow, and the ability to adjust attachment force in response to hydrodynamic conditions. A broad taxonomic range of adult stages use adhesion or suction to attach to hard substrates in intertidal habitats, which experience flow from waves and tidal currents. We address the unique challenges of attachment to soft sediment in reproductive structures deposited on tidal flats. Egg masses of the opisthobranch mollusc Melanochlamys diomedea are anchored to the sediment by a buried tether composed of gel and sediment. In the field, populations differed in absolute tethering force and tethering force per unit size (= tenacity). Population differences in tenacity persisted for egg masses oviposited under common conditions in the laboratory. Adults exposed to greater flow produced tethers with greater tenacity but without an increase in tether size. Tethers tended to fail by slippage rather than breakage, indicating that tethering force depends more on frictional interaction with sediment than on strength of the tether axis. These results suggest that adults respond to variation in risks of embryo dislodgment by adjusting the tethering properties of egg masses, and that these adjustments involve more than simple changes in tether length or mass.

Cover Picture: Biosynthesis and Cellular Localization of Functional Polyketides in the Gastropod Mollusc Scaphander lignarius (ChemBioChem 12/2012)

The cover picture shows the biosynthesis, in the specialized tissue of the opisthobranch mollusc Scaphander lignarius, of the aromatic semiochemical lignarenones. Opisthobranchs are a special group of marine invertebrates that are very well known as an extraordinary source of bioactive natural products. In the article on p. 1759 ff., A. Fontana et al. show that the biosynthesis of lignarenones takes place in specialized mantle cells, the Blochmann's glands, by an unprecedented benzenoid pathway. Synthesis of the polyketide skeleton requires a mixed acetate–propionate assembly that is primed by benzoic acid derived from L-phenylalanine. This last process is gated by enzymatic nonoxidative deamination of the amino acid; this is reminiscent of the transformation catalyzed by phenylalanine ammonia lyases (PALs) in plants and fungi. The article suggests that marine invertebrates possess their own competence for the biosynthesis of natural products, thus challenging the present view on the universal role of microorganisms as the source of functional products in marine benthos.

First report on reproduction of lessepsian ragged sea hare, Bursatella leachii de Blainville, 1817 (Mollusca: Gastropoda) in Izmir Bay (Aegean Sea, Turkey)

The ragged sea hare, Bursatella leachii De Blainville, 1817, is a medium to large-sized (usu-ally from 50 to 100 mm, up to 150 mm) benthic opisthobranch mollusc (Voss, 1980; CIESM, 2002). It is a circumtropical species found nearly worldwide in warm temperate to tropical marine environments and it is common in intertidal and subtidal sheltered bay and estuarine habitats with sand or muddy bottoms, and are a frequently en-countered component of tropical and subtropical sea grass and mangrove communities

Six new species of aglajid opisthobranch mollusks from the tropical Indo-Pacific

Six new species of aglajid opisthobranchs are described from various localities in the tropical Indo-Pacific. Philinopsis falciphallus n. sp., found from the Marshall Islands to the Red Sea, is distinguished by its reddish body color, a distinct black or maroon longitudinal line on the foot, a posterior projection on the posterior shield and a penis with a chitinous, sickle-shaped spine and numerous smaller spines. Philinopsis coronata n. sp., known only from the Philippines, is similar to P. falciphallus but dominated by yellow body color and a ventral surface of the foot with yellow and maroon spots. It has a trumpet-shaped penis with a crown of rounded tubercles on the apex and anterior and posterior zones of penial spines. Philinopsis ctenophoraphaga n. sp. is found from the Philippines, Indonesia and the Red Sea. It feeds on platyctene ctenophores, including Coeloplana meteroris. It can be distinguished by its elongate posterior lobe of the headshield, reddish color with white spots, thinly muscularized buccal mass and simple, unarmed penis. Chelidonura mandroroa n. sp. is characterized by its black body with orange patches lined by yellow. It has a simple penis with a cuticularized apical papilla. This species has been found from Japan, Taiwan, the Philippines, Indonesia, Madagascar and Kenya. Chelidonura alisonae n. sp. is apparently restricted to the central and eastern Pacific of the Hawai’ian Islands, Johnston Island, the Marianas Islands and Easter Island. It is similar in coloration to C. hirundinina, but has orange lines on the dorsal and lateral shields and has a broad right posterior lobe rather than an acutely pointed one. The penis is simple and unarmed. Odontoglaja mosaica n. sp., found from the Indian Ocean of Madagascar and South Africa, differs from O. guamensis by possessing a reticulate pattern on the notum rather than a pattern of brown spots. It also has a shorter penial papilla that is bifurcate rather than undivided one.

The transcriptome of the early life history stages of the California Sea Hare Aplysia californica

Aplysia californica is a marine opisthobranch mollusc used as a model organism in neurobiology for cellular analyses of learning and behavior because it possesses a comparatively small number of neurons of large size. The mollusca comprise the second largest animal phylum, yet detailed genetic and genomic information is only recently beginning to accrue. Thus developmental and comparative evolutionary biology as well as biomedical research would benefit from additional information on DNA sequences of Aplysia. Therefore, we have constructed a series of unidirectional cDNA libraries from different life stages of Aplysia. These include whole organisms from the egg, veliger, metamorphic, and juvenile stages as well as adult neural tissue for reference. Individual clones were randomly picked, and high-throughput, single pass sequence analysis was performed to generate 7971 sequences. Of these, there were 5507 quality-filtered ESTs that clustered into 1988 unigenes, which are annotated and deposited into GenBank. A significant number (497) of ESTs did not match existing Aplysia ESTs and are thus potentially novel sequences for Aplysia. GO and KEGG analyses of these novel sequences indicated that a large number were involved in protein binding and translation, consistent with the predominant biosynthetic role in development and the presence of stage-specific protein isoforms.

Description of a new genus Praephiline gen. nov. (Gastropoda: Opisthobranchia: Philinidae)

A new genus of opisthobranch mollusks Praephiline gen. nov. is described for Philine finmarchica M. Sars, 1858. Philine finmarchica differs significantly from the type of Philine - Philine aperta in the morphology of gizzard and male copulatory apparatus. The status of Philine thurmanni thurmanni Marcus & Marcus, 1969 and Philine thurmanni chilla Marcus & Marcus, 1969 is discussed; they are considered to be distinct species and assigned to the new genus - Praephiline thurmanni (Marcus & Marcus, 1969) and Praephiline chilla (Marcus & Marcus, 1969).

Conservation of the egg-laying hormone neuropeptide and attractin pheromone in the spotted sea hare, Aplysia dactylomela

In the marine opisthobranch mollusc, Aplysia, secreted peptides and proteins play an essential role in egg laying and mate attraction. Aplysia californica egg laying is initiated by secretion of the egg-laying hormone (ELH) peptide while mate attraction is made possible by protein pheromones, such as attractin, released into the surrounding seawater with the egg cordon. In this study, we investigated the existence of similar egg-laying hormone and attractin products in the spotted sea hare, Aplysia dactylomela, a species that is widely distributed in almost all tropical and temperate oceans, including Australia's Great Barrier Reef. Immunological analysis revealed that an ELH-like transmitter is present within bag cell somata and processes of the abdominal ganglion. A molecular genetic approach found that the ELH precursor mRNA is synthesized in the abdominal ganglia and encodes a 36-residue peptide (dELH) that is cleaved from the prohormone prior to secretion. It is most closely related to A. californica and A. brasiliana ELH (91.7% identical). We also found that A. dactylomela synthesize an attractin pheromone in the albumen gland that is released during egg laying. The gene encodes a 58-residue mature protein that is 74.9% similar to A. californica attractin. We demonstrate that an increase in seawater temperature can disrupt attractins higher order interactions, such as those with the pheromone temptin, and accelerates attractin degradation. Together, these findings further expands our understanding of pheromone intermolecular interactions and presents an opportunity for further study of how increases in sea water temperature may affect this important marine communication system.

Comparative morphology of the hammer-shaped penisesof two species of opisthobranch mollusсs of the genus Philine Ascanius, 1772 (Opisthobranchia: Cephalaspidea: Philinidae)

Penises of two species of opisthobranch mollusks of Philine were first examined with use of a scanning electron microscope: Ph. aperta (Linnaeus, 1767) and P. finmarchica M. Sars, 1858. This study revealed significant morphological differences. The morphology of male copulatory apparatus of these species is discussed

First Record of a Pearlfish, Carapus mourlani, Inhabiting the Aplysiid Opisthobranch Mollusc Dolabella auricularia1

Adult individuals of the pearlfish Carapus mourlani (Petit, 1934) occur commonly in the mantle cavity of the opisthobranch mollusc Dolabella auricularia (Lightfoot, 1786) in shallow marine waters of the Gulf of Chiriquí, Pacific Panamá. Nearly 30% of the molluscan hosts collected during the day on a coral reef contained one or two fish. Feeding observations of a captive fish as well as the intact condition of the host's ctenidium and other internal organs suggest that C. mourlani is an inquiline commensal and not parasitic. Fish curl around the ctenidium during the day and capture microcrustaceans when the fish emerge from their host at night to feed. From low-light infrared video recordings, Carapus was observed to accurately grasp rapidly swimming amphipods in nearly total darkness and ingest them. This symbiotic relationship appears to benefit Carapus by allowing the fish to avoid predators during the day and to forage at night.

Two New Species of Doridicola (Copepoda: Cyclopoida: Rhynchomolgidae) Associated with Opisthobranch Mollusks from Korea

Two new species of the genus Doridicola are described as associates of opisthobranch mollusks from Korean intertidal waters: Doridicola virguatus n. sp. associated with the notaspidean Pleurobranchaea japonica Thiele and D. portincola n. sp. associated with the nudibranch Hoplodoris armata (Baba). This is the first record for the copepod associates of opisthobranch mollusks from Korea.

Cellular analysis of a molluscan retinal biological clock.

The eye of the opisthobranch mollusc Bulla gouldiana expresses a circadian rhythm in optic nerve impulse frequency. The circadian rhythm is generated among approximately 100 neurons at the base of the retina referred to as basal retinal neurons. These cells are electrically coupled to one another and fire spontaneous action potentials in synchrony. Basal retinal neurons recorded intracellularly exhibit a circadian rhythm in membrane potential that appears to be driven by a circadian modulation of membrane conductance. Membrane conductance is relatively high during the subjective night and decreases after subjective dawn. Recent experiments in our laboratory indicate that individual basal retinal neurons in culture can express circadian rhythms in membrane conductance. When completely isolated, these cells continue to show circadian conductance changes. These studies provide the first direct demonstration that individual neurons can act as circadian pacemakers. Although the precise details of the mechanism generating the circadian periodicity remain obscure, our research indicates that several transmembrane ionic fluxes are not involved in rhythm generation, but that a transmembrane Ca2+ flux is critical for entrainment. Both transcription and translation appear to play critical roles in generating the circadian cycle.

Localization of putative nitrergic neurons in peripheral chemosensory areas and the central nervous system ofAplysia californica

The distribution of putative nitric oxide synthase (NOS)-containing cells in the opisthobranch mollusc Aplysia californica was studied by using NADPH-diaphorase (NADPH-d) histochemistry in the CNS and peripheral organs. Chemosensory areas (the mouth area, rhinophores, and tentacles) express the most intense staining, primarily in the form of peripheral highly packed neuropil regions with a glomerular appearance as well as in epithelial sensory-like cells. These epithelial NADPH-d-reactive cells were small and had multiple apical ciliated processes exposed to the environment. NADPH-d processes were also found in the salivary glands, but there was no or very little staining in the buccal mass and foot musculature. In the CNS, most NADPH-d reactivity was associated with the neuropil of the cerebral ganglia, with the highest density of glomeruli-like NADPH-d-reactive neurites in the areas of the termini and around F and C clusters. A few NADPH-d-reactive neurons were also found in other central ganglia, including paired neurons in the buccal, pedal, and pleural ganglia and a few asymmetrical neurons in the abdominal ganglion. The distribution patterns of NADPH-d-reactive neurons did not overlap with other known neurotransmitter systems. The highly selective NADPH-d labeling revealed here suggests the presence of NOS in sensory areas both in the CNS and the peripheral organs of Aplysia and implies a role for NO as a modulator of chemosensory processing.

Dietary selectivity for the toxic cyanobacterium Lyngbya majuscula and resultant growth rates in two species of opisthobranch mollusc

Trophodynamics of blooms of the toxic marine cyanobacterium Lyngbya majuscula were investigated to determine dietary specificity in two putative grazers: the opisthobranch molluscs, Stylocheilus striatus and Bursatella leachii. S. striatus is associated with L. majuscula blooms and is known to sequester L. majuscula metabolites. The dietary specificity and toxicodynamics of B. leachii in relation to L. majuscula is less well documented. In this study we found diet history had no significant effect upon dietary selectivity of S. striatus when offered a range of plant species. However, L. majuscula chemotype may alter S. striatus' selectivity for this cyanobacterium. Daily biomass increases between small and large size groups of both species were recorded in no-choice consumption trials using L. majuscula. Both S. striatus and B. leachii preferentially consumed L. majuscula containing lyngbyatoxin-a. Increase in mass over a 10-day period in B. leachii (915%) was significantly greater than S. striatus (150%), yet S. striatus consumed greater quantities of L. majuscula (g day − 1 ) and thus had a lower conversion efficiency (0.038) than B. leachii (0.081) based on sea hare weight per gram of L. majuscula consumed day − 1 . Our findings suggest that growth rates and conversion efficiencies may be influenced by sea hare maximum growth potential, acquisition of secondary metabolites or diet type.

Sperm storage and use in laboratory-reared Aplysia californica , a simultaneous hermaphrodite

Aplysia californica, an opisthobranch mollusc, possesses a complex reproductive system that includes a seminal receptacle for the storage of exogenous sperm received from mating. Based on this reproductive anatomy, A. californica should have the ability to maintain and use viable exogenous sperm stores to fertilize multiple eggmasses for extended periods of time. Using controlled matings and careful observation of the development of eggmasses over time, we attempted to quantify A. californica’s ability to store and use exogenous sperm following a single mating. On average, A. californica (240.6±31.7 g; mean±SE, n=9) produced 8.8±0.6 eggmasses containing 16.9±2.2×106 fertilized eggs over a period of 22.3±3.6 days following a single mating encounter. The maximum duration an individual A. californica produced fertilized eggs, following a single copulation, was 41 days. The primary factor determining the cumulative number of fertilized eggs produced from a single mating in A. californica was the mass of the sperm recipient (r=0.773, P<0.05, n=9). Our results demonstrated that A. californica are not sperm limited following a single mating as has been suggested for other opisthobranch molluscs by Leonard and Lukowiak’s (1991) gamete-trading hypothesis.

Apoptotic‐like morphology is associated with annual synchronized death in kleptoplastic sea slugs (Elysia chlorotica)

Abstract. Certain digestive cells of the opisthobranch mollusc, Elysia chlorotica, contain functional chloroplasts which they steal from the filamentous alga, Vaucheria litorea. The adult portion of the life cycle of the slug lasts for ∼10 months and is completely synchronized among individuals. All the adults die each year within a few weeks of each other. We have examined the microscopic morphology of the slugs near the end of the life cycle. Light microscopy demonstrated an absence of chloroplasts in most of the digestive epithelial cells, the appearance of many crypt cells containing residual bodies and an invasion of the blood sinuses by neoplastic morula‐like cells as the animals die. Electron microscopy revealed a degeneration of the digestive diverticulum which had several morphological characteristics in common with apoptosis: expansion of the endoplasmic reticulum and Golgi apparatus, DNA fragmentation, formation of primary lysosomes, and condensation of chromatin. These are followed by fragmentation of the nucleus and cytoplasm into autosomes merging to form a large central autolysosome. In addition in the aging slugs, the plastids begin to degenerate until none were left in the digestive epithelial cells and the central autolysosome contained numerous viral particles.

Joseph S. Takahashi, Fred W. Turek and Robert Y.Moore (eds): Circadian Clocks (Handbook of Behavioral Neurobiology, Vol 12)

Circadian Clocks (Handbook of Behavioral Neurobiology, Vol. 12) Takahashi, Joseph S., Turek, Fred W. and Moore, Robert Y. (eds) Kluwer Academic/Plenum Publishers 2001 , $175 , 794 pages, ISBN 0-306-46504-3 Most organisms have been forced to adapt to the once-daily rotation of our planet on its axis. The geophysical day–night cycle is not only reflected as circadian (Latin: circa = about, dies = day) rhythms of physiology and behavior, but is also actually incorporated within organisms as a genetically determined temporal program. This endogenous, temperature-compensated timekeeping mechanism recognizes local time, measures its passage, and contributes to the regulation of homeostasis, seasonal behavior, and migration. Evidence for its existence was still being debated as late as 1960, but by 1981 the field had advanced to such a stage that it was reviewed in Volume 4 of the new Handbook of Behavioral Neurobiology. At that time, single gene mutants affecting rhythms in flies and fungi had been isolated, and the suprachiasmatic nucleus (SCN) was being proposed as a candidate circadian clock in mammals, but the terms ‘genetics’, ‘neurotransmitter’, and ‘shift work’ were not yet listed in the index. In the editor's preface, Jürgen Aschoff wrote, ‘The study of the physiological mechanisms underlying circarhythms is a rapidly developing field, and the question of how discrete is the clock from the rest of the body…may soon be answered in the circadian case…’. Twenty years have now passed and our progress has been almost unimaginable. Among other advances, the body of evidence that has identified the SCN as a master circadian pacemaker is so compelling and multidisciplinary that the strength of this functional localization is unsurpassed by that of any other structure in the vertebrate brain. We have discovered intracellular regulatory molecules and biochemical processes that are likely to constitute the actual oscillatory mechanism of the clock. The practical application of our new knowledge has been recognized, and chronobiologists now advise astronauts. Volume 12 of the Handbook, Circadian Clocks, summarizes how extraordinarily far we have come. It is a comprehensive and authoritative reference work of 26 chapters in 6 parts. Included are chapters on entrainment theory and the ecology and evolution of circadian rhythmicity; on the organization of circadian systems, from unicells to invertebrates and non-mammalian and mammalian vertebrates; on the regulation of mammalian rhythmicity, including photic and non-photic entrainment, development and aging, sleep and wakefulness, and seasonality; on cellular and molecular mechanisms in Synechococcus, Gonyaulax, Neurospora, Drosophila, opisthobranch mollusks, and rodents; and on the human circadian system and its role in sleep, performance, aging, affective disorders, endocrine secretion, and photoperiodic responses. The book is handsomely produced and certain to become a manual for molecular biologists, neuroscientists, physiologists, and physicians working on circadian rhythms. While no existing book matches the scope of Circadian Clocks, a few topics are missing even from this volume. Not considered are the clocks of higher plants, or the role of clocks in tidal rhythms and sun compass orientation. There is little, if any, coverage of how circadian rhythms might impact medical practice, i.e. by influencing the timing of pharmacotherapy or the manifestations of disease. Finally, some chapters on molecular mechanisms were apparently written five years ago and are a bit outdated, although the field is moving so fast anyway that it would be impossible for any book to be completely up to date. So, some remarkable new stories – the mutant clock genes responsible for advanced sleep phase syndrome, the role of peripheral oscillators in body rhythmicity, and the identification of candidate circadian photoreceptors and molecules – will need to wait for the next volume. Circadian Clocks clearly shows why the circadian timekeeping system has become such a unique and powerful model for studying genes, brain and behavior. There are remarkable opportunities to begin to understand a biological system at multiple levels of organization, ranging from the regulation of gene expression, to intercellular networks and multisynaptic pathways, and finally to integrated patterns of physiology and performance. Clock investigators include geneticists cloning clock genes, zoologists examining rhythmic behaviors in the wild, neurophysiologists recording spike trains in the hypothalamus, and psychiatrists treating patients with seasonal affective disorder (to name just a few). By enhancing the dialogue between these researchers and their disciplines, Circadian Clocks should serve as a very valuable resource. William J. Schwartz Department of Neurology University of Massachusetts Medical School 55 Lake Ave. North Worcester MA 01655, USA

Swimming in Opisthobranch Mollusks: Contributions to Control of Motor Behavior: Introduction to the Symposium1

Beginning with the pioneering work of Dennis Willows (Willows and Hoyle, 1969; Willows et al. , 1973), studies utilizing opisthobranch mollusks have been particularly useful in the description of rhythmic motor behaviors and their mechanisms of central pattern generation. General mechanisms that contribute to central pattern generator function in other animal groups, such as reciprocal inhibition, postinhibitory rebound, multi-component synaptic potentials, delayed excitation, and extrinsic modulation (to name a few), have been found to contribute to the generation of rhythmic motor behavior in opisthobranchs. In addition, some novel concepts that have since been substantiated in other animal groups were developed through work on opisthobranch locomotory systems: some CPG neurons are multifunctional and may participate in different motor behaviors (Getting, 1989); networks can be intrinsically modulated by components within the CPG networks (Katz et al. , 1994; Katz and Frost, 1995). The Opisthobranch Swimming symposium was organized with a primary goal of providing details of motor control from four specific Opisthobranch orders that have swimming members. This comparative approach is particularly interesting since behavioral observations of swimming activity in the four orders reveal three distinct types of swimming. In the Anaspids ( Aplysia ) and Gymnosomes ( Clione ), swimming is accomplished by flapping of parapodia. In the latter group, parapodia are highly modified into wings. In the Notaspids ( Pleurobranchaea ) and dorso-ventrally flattened Nudibranchs ( Tritonia ), swimming consists of alternate dorsal and ventral flexions of the body. Finally, in the laterally flattened Nudibranchs ( Melibe ), swimming occurs with alternating lateral flexions of the body. In all but one case ( Clione ), the central neural circuits and effectors for swimming also participate in other behaviors. For example, the parapodia of Aplysia undergo local protective contractions in response to directed stimulation and produce coordinated respiratory pumping contractions in addition to their role in swimming (Kandel, 1979). In …

Swimming in Opisthobranch Mollusks: Contributions to Control of Motor Behavior: Introduction to the Symposium

Swimming in Opisthobranch Mollusks: Contributions to Control of Motor Behavior: Introduction to the Symposium

Chemical defenses of the sacoglossan mollusk Elysia rufescens and its host Alga bryopsis sp.

Sacoglossans are a group of opisthobranch mollusks that have been the source of numerous secondary metabolites; however, there are few examples where a defensive ecological role for these compounds has been demonstrated experimentally. We investigated the deterrent properties of the sacoglossan Elysia rufescens and its food alga Bryopsis sp. against natural fish predators. Bryopsis sp. produces kahalalide F, a major depsipeptide that is accumulated by the sacoglossan and that shows in vitro cytotoxicity against several cancer cell lines. Our data show that both Bryopsis sp. and Elysia rufescens are chemically protected against fish predators, as indicated by the deterrent properties of their extracts at naturally occurring concentrations. Following bioassay-guided fractionation, we observed that the antipredatory compounds of Bryopsis sp. were present in the butanol and chloroform fractions, both containing the depsipeptide kahalalide F. Antipredatory compounds of Elysia rufescens were exclusively present in the dichloromethane fraction. Further bioassay-guided fractionation led to the isolation of kahalalide F as the only compound responsible for the deterrent properties of the sacoglossan. Our data show that kahalalide F protects both Brvopsis sp. and Elysia rufescens from fish predation. This is the first report of a diet-derived depsipeptide used as a chemical defense in a sacoglossan.