Characterization of cardiac innervation in the nudibranch,Archidoris montereyensis

Summary The heart of the nudibranch mollusc Archidoris montereyensis is regulated by a small number of powerful effector neurons located in the right pleural and visceral ganglia. Two identifiable neurons in the pleural ganglion, a heart excitor (pl_HE) and a heart inhibitor (Pl_HI), are especially important regulators of cardiac function in that low levels of spontaneous activity in either cell significantly alters the amplitude and rate of heart contractions. These neurons have extensive dendritic arbors within the right pleural ganglion and branching axonal processes within the visceral ganglion. The visceral ganglion also contains a heart excitor neuron (V_HE) and at least two heart inhibitor neurons (V_HI cells), but their influence on cardiac activity is weaker than that of the pleural ganglion cells. All of these heart effector cells appear to be motor neurons with axons that terminate predominately in the atrio-ventricular valve region of the heart via the pericardial nerve. The simplicity and strength of these neuronal connections to the heart of Archidoris make this a favorable preparation for studies of cardiac regulation.Abbreviations Pl _HE pleural ganglion heart excitor neuron - Pl _HI pleural heart inhibitor neuron - V _HE visceral ganglion heart excitor neuron - V _HI cells, visceral heart inhibitor neurons - V _K visceral kidney excitor neuron - V _G visceral gill excitor neuron     

Fine structural study of the statocysts in the veliger larva of the nudibranch,Rostanga pulchra

Summary The two statocysts of the veliger larva of Rostanga pulchra are positioned within the base of the foot. They are spherical, fluid-filled capsule that contain a large, calcareous statolith and several smaller concretions. The epithelium of the statocyst is composed of 10 ciliated sensory cells (hair cells) and 11 accessory cells. The latter group stains darkly and includes 2 microvillous cells, 7 supporting cells, and 2 glial cells. The hair cells stain lightly and each gives rise to an axon; two types can be distinguished. The first type, in which a minimum of 3 cilia are randomly positioned on the apical cell membrane, is restricted to the upper portion of the statocyst. The second type, in which 9 to 11 cilia are arranged in a slightly curved row, is found exclusively around the base of the statocyst. Each statocyst is connected dorso-laterally to the ipsilateral cerebral ganglion by a short static nerve, formed by axons arising from the hair cells. Ganglionic neurons synapse with these axons as the static nerve enters the cerebral ganglion. The lumen of the statocyst is continuous with a blind constricted canal located beneath the static nerve.A diagram showing the structure of the statocyst and its association with the nervous system is presented. Possible functions of the statocyst in relation to larval behavior are discussed.     

Invasive species as a new food source: does a nudibranch predator prefer eating an invasive bryozoan?

Membranipora membranacea is an invasive bryozoan that was first found in the Gulf of Maine in 1987 and within two years became the dominant organism living on kelps. Membranipora may have become dominant so quickly because it had little competition in a relatively unoccupied niche; however, lack of predation has also probably played a major role. Where Membranipora is native, there is usually a specialist nudibranch predator that keeps the population in check. For example, in European populations, the nudibranch Polycera quadrilineata prefers Membranipora while Onchidoris muricata is known to prefer another bryozoan, Electra pilosa. Electra, Membranipora, and Onchidoris are all now found in the Gulf of Maine while Polycera is not. We tested whether Onchidoris would (1) eat Membranipora at all, (2) eat Membranipora and Electra at different rates, and (3) show a preference for eating Membranipora or Electra when given a choice. We found that Onchidoris does eat Membranipora, and it generally eats Membranipora faster than Electra. However, when given a choice, Onchidoris prefers Electra. Onchidoris typically reproduces in the spring and grows over the fall and winter, but has recently been found reproducing in the winter in New Hampshire. Although it does not survive the winter as well as Electra, Membranipora is the dominant organism living on many macroalgae in the late summer and fall. Thus, the large Membranipora food source now available in the summer and fall may allow Onchidoris to reproduce earlier.     

Nudibranch-sponge feeding dynamics: Benefits of symbiont-containing sponge to Archidoris montereyensis (Cooper, 1862) and recovery of nudibranch feeding scars by Halichondria panicea (Pallas, 1766)

Selected interactions between the encrusting sponge Halichondria panicea and its primary predator, the dorid nudibranch Archidoris montereyensis, were investigated in a high-latitude rocky intertidal community spatially dominated by H. panicea. Feeding experiments were conducted in which A. montereyensis pairs were provided with sponge containing symbiotic zoochlorellae or sponge in which the zoochlorellae population had been reduced or removed by shading. Nudibranchs consuming H. panicea with symbiotic zoochlorellae had higher feeding, growth, and egg production rates than individuals eating aposymbiotic sponge. We simulated A. montereyensis predation on H. panicea by creating typically sized feeding grooves in the sponge. H. panicea's response was high linear growth rates into the experimental feeding grooves, generally recovering most of the groove area within 4 weeks. Overall, the sponge's rapid response to tissue damage minimizes grazing impacts and substrate loss and reduces susceptibility to wave removal.     

Wave-related abrasion induces formation of extended spines in a marine bryozoan

Inducible morphology, the conditional expression of morphological characters under certain environmental regimes, is a trait usually found in organisms subject to discrete environmental variability. In marine invertebrates, inducible changes in morphology are usually linked to unpredictable attack by predators or overgrowth competition. We present here evidence that extended spine formation in the marine bryozoan Electra pilosa is inducible by an abiotic cue, wave-related abrasion. In a laboratory experiment, we induced the formation of extended spines by subjecting colonies of E. pilosa to abrasion by seaweeds. We also investigated the potential role of Adalaria proxima, a specialist suctorial nudibranch predator of E. pilosa, in the formation of extended spines. While the presence of the predator does not itself induce extended spine formation, the spines do have a fortuitous anti-predator effect, discouraging predation both by A. proxima and another nudibranch, Polycera quadrilineata. We suggest that extended spines in E. pilosa constitute an adaptation for the protection of feeding polypides in high-energy environments, and that plasticity for the trait is of adaptive value this passively dispersed organism, which exploits in a diverse range of substrata and epifaunal habitats.     

Abundance,feeding behaviour and nematocysts of scyphopolyps (Cnidaria) and nematocysts in their predator,the nudibranch Coryphella verrucosa (Mollusca)

The abundance of Aurelia and Cyanea scyphopolyps on Laminaria saccharinawas higher in sheltered, shallow areas compared with more exposed or deepones. Liberated planulae probably were not transported far away fromstranded and trapped jellyfish and settled nearby, preferably in patches onthe downward side of the Laminaria thallus. The principal prey for thescyphopolyps seems to be small copepods and the cladocerans Podon sp. andEvadne sp., which are abundant in surface waters during the summer.Temporarily abundant planktonic organisms, e.g., Sagitta setosa,Pleurobrachia pileus and hydromedusae might, also be important prey.Harpacticids, halacarideans and Corophium sp., whose natural habitat is onL. saccharina, were not captured by the scyphopolyps. Scyphopolyps culturedin running sea water rich in detritus and phytoplankton fill their enteronwith organic substrates, particularly diatoms. A new category ofheterotrichous microbasic rhopaloid nematocysts was identified in thescyphopolyps. These rhopaloids were earlier included within the eurytelesand were not considered to be separate nematocysts. They are distinctivefrom the euryteles due to the two swellings on their discharged shaft. Theabsence or presence of the nudibranch Coryphella verrucosa on laminarianthalli possibly has an effect on the number of scyphopolyps, as thisnudibranch consumes numerous scyphopolyps. Isorhizas and the new category ofrhopaloid nematocysts, identical to those present in the Aurelia polyps,occurred in the cnidosacs of examined C. verrucosa. The proportion ofrhopaloid nematocysts compared with a-isorhizas was noticeably higher in C.verrucosa than in scyphopolyps. The nudibranch may selectively storerhopaloids.     

The influence of light on locomotion in the gastropod melibe leonina

In this study, we investigated the effects of light on both the locomotion of intact animals and the swim motor program expressed by isolated brains in the gastropod Melibe leonina. Spontaneous locomotion (crawling and swimming) was examined during a period of natural lighting (L:D) to establish normal behavior, and then under two different light regimes: constant darkness (D:D) and constant light (L:L). In L:D, there was significantly more locomotor activity at night than during the day and this pattern continued in D:D. However, in L:L, activity was substantially reduced at all times. Using isolated brain preparations, we further demonstrated that the swim motor program was rapidly inhibited by light, and that this inhibition was mediated by the eyes. These results indicate that M. leonina displays a nocturnal activity pattern, and that light has a strong inhibitory effect on locomotion in the intact animal and on the swim motor program expressed by the isolated brain.     

Active Nematocyst Isolation Via Nudibranchs

Cnidarian venoms are potentially valuable tools for biomedical research and drug development. They are contained within nematocysts, the stinging organelles of cnidarians. Several methods exist for the isolation of nematocysts from cnidarian tissues; most are tedious and target nematocysts from specific tissues. We have discovered that the isolated active nematocyst complement (cnidome) of several sea anemone (Cnidaria: Anthozoa) species is readily accessible. These nematocysts are isolated, concentrated, and released to the aqueous environment as a by-product of aeolid nudibranch Spurilla neapolitana cultures. S. neapolitana feed on venomous sea anemones laden with stinging nematocysts. The ingested stinging organelles of several sea anemone species are effectively excreted in the nudibranch feces. We succeeded in purifying the active organelles and inducing their discharge. Thus, our current study presents the attractive possibility of using nudibranchs to produce nematocysts for the investigation of novel marine compounds.     

Fine structure of the larval rhinophores of the nudibranch,Rostanga pulchra,with emphasis on the sensory receptor cells

Summary The rhinophores of the veliger larva of Rostanga pulchra are located in the intravelar field near the base of the velar lobes. Each rhinophore is a cylindrical structure, tapering distally, and covered with a dense meshwork of microvilli. A conspicuous row of ciliary tufts runs along each side of the rhinophore and several stiffer tufts, composed of fewer cilia, are positioned around the tip or at the base. The rhinophoral epithelium consists of supporting cells, ciliated cells (giving rise to the ciliary rows), dendritic terminals (giving rise to the tufts around the apex), and sinuses containing occasional amebocytes. The lumen of the rhinophore is occupied by the rhinophoral ganglion and muscle cells that are oriented in two perpendicular planes. Cell bodies of the dendritic endings are located within the rhinophoral ganglion, which in turn joins into the optic and cerebral ganglia. Rhinophoral ganglionic neurons do not synapse with each other, but numerous neuromuscular synapses are found in the lumen of the rhinophore.Morphological evidence suggests that the dendritic endings are chemoreceptors and the ciliated cells are possibly mechanoreceptors but are not functional at this stage in development. The functional role of the rhinophores is discussed in relation to larval behavior at settlement and metamorphosis.     

Measuring recruitment of minute larvae in a complex field environment: The corallivorous nudibranch Phestilla sibogae (Bergh)

The nudibranch Phestilla sibogae feeds only on corals of the genus Porites. The nudibranch's minute (∼ 200 μm) larvae are specifically induced to settle and metamorphose by a chemical cue released by the coral, causing the larvae to recruit to reefs composed predominantly of Porites compressa. In this study, we investigated temporal and spatial patterns of recruitment of P. sibogae into coral reefs in Kane?ohe Bay, HI. We collected heads of P. compressa at 3-week intervals for 3 years, brought them to the laboratory and maintained them in aquaria fed with filtered seawater for 2 weeks, and then examined them for the presence of juvenile P. sibogae that had grown large enough to be seen. We found that P. sibogae recruits to the Porites reefs of Kane?ohe Bay sporadically and unpredictably throughout the year. Although most coral samples contained no or very few P. sibogae, three periods of intense recruitment (90-450 juvenile P. sibogae kg^− 1 of coral) were recorded, all in different seasons. Size-frequency analysis of recruits on the coral revealed high rates of post-settlement mortality in the field, most likely due to predation. Given the short pre-competent larval period of P. sibogae, the low rate of flushing of Kane?ohe Bay and the patterns of recruitment observed, we conclude that this population of P. sibogae is essentially a self-recruiting one. Two of the sampled reefs were characterized by unidirectional flow, allowing us to test a model of transport of larvae of P. sibogae responding to dissolved coral cue in turbulent, wavy flow. The model predicts that more larvae will be transported into upstream portions of a reef than into downstream portions, a prediction confirmed by analysis of the field-recruitment data. Furthermore, field releases of larval mimic particles also showed that most mimics landed in the upstream areas of reefs and down among the bases of coral branches, rather than at their tips.