Myoanatomy and serotonergic nervous system of plumatellid and fredericellid phylactolaemata (lophotrochozoa,ectoprocta)

The phylogenetic position of the Ectoprocta within the Lophotrochozoa is discussed controversially. For gaining more insight into ectoproct relationships and comparing it with other potentially related phyla, we analysed the myoanatomy and serotonergic nervous system of adult representatives of the Phylactolaemata (Plumatella emarginata, Plumatellavaihiriae, Plumatella fungosa, Fredericella sultana). The bodywall contains a mesh of circular and longitudinal muscles. On its distal end, the orifice possesses a prominent sphincter and continues into the vestibular wall, which has longitudinal and circular musculature. The tentacle sheath carries mostly longitudinal muscle fibres in Plumatella sp., whereas F. sultana also possesses regular circular muscle fibres. Three groups of muscles are associated with the lophophore: 1) Lophophoral arm muscles (missing in Fredericella), 2) epistome musculature and 3) tentacle musculature. The epistome flap is encompassed by smooth muscle fibres. A few fibres extend medially over the ganglion to its proximal floor. Abfrontal tentacle muscles have diagonally arranged muscle fibres in their proximal region, whereas the distal region is formed by a stack of muscles that resemble an inverted ‘V’. Frontal tentacle muscles show more variation and either possess one or two bases. The digestive tract possesses circular musculature which is striated except at the intestine where it is composed of smooth muscle fibres. The serotonergic nervous system is concentrated in the cerebral ganglion. From the latter a serotonergic nerve extends to each tentacle base. In Plumatella the inner row of tentacles at the lophophoral concavity lacks serotonergic nerves. Bodywall musculature is a common feature in many lophotrochozoan phyla, but among other filter feeders like the Ectoprocta is only present in the ‘lophophorate’ Phoronida. The longitudinal tentacle musculature is reminiscent of the condition found in phoronids and brachiopods, but differs to entoproct tentacles. Although this study shows some support for the ‘Lophophorata’, more comparative analyses of possibly related phyla are required. J. Morphol., 2011. © 2011 Wiley Periodicals, Inc.     

On natural metamorphosis inducers of the cnidarians Hydractinia echinata (Hydrozoa) and Aurelia aurita (Scyphozoa)

 Hydractinia echinata and Aurelia aurita produce motile larvae which undergo metamorphosis to sessile polyps when induced by external cues. The polyps are found at restricted sites, A. aurita predominantly on rocks close to the shore, H. echinata on shells inhabited by hermit crabs. It has been argued that the differential distribution of the polyps in their natural environment largely reflects the distribution of the natural metamorphosis-inducing cues. In the case of H. echinata, bacteria of the genus Alteromonas were argued to meet these conditions. We found that almost all substrates collected in the littoral to induce metamorphosis in H. echinata, and several bacterial strains isolated from the sea, including the common E. coli, induce metamorphosis efficiently. In A. aurita metamorphosis may be induced by the water–air interface, whereby metamorphosis precedes (final) settlement. Received: 7 December 1998 / Accepted: 8 July 1999     

Temperature effects on asexual reproduction rates of scyphozoan species from the northwest Mediterranean Sea

In recent decades, many areas worldwide have experienced mass occurrences of jellyfish. To determine how temperature may affect jellyfish populations in the northwest (NW) Mediterranean Sea, we maintained polyps of three scyphozoan species, Aurelia aurita, Rhizostoma pulmo, and Cotylorhiza tuberculata in the laboratory at three temperatures (14, 21, 28°C) to test effects on survival and production of new polyps and ephyrae. Temperature significantly affected survival of all species, with longest survival of A. aurita and R. pulmo at 14°C and of C. tuberculata at 21°C. More polyps were budded by all species at temperatures above 14°C. A. aurita produced the most buds polyp⁻¹ (43.5) and R. pulmo the fewest (8.8). Strobilation occurred only at 14°C for A. aurita and at 21°C for C. tuberculata. For R. pulmo, fewer polyps strobilated and strobilated later at 14°C. These patterns of survival and asexual reproduction were seasonally appropriate for each species in the NW Mediterranean, where A. aurita medusae occur earliest (~April–May) in cool waters, followed by R. pulmo during May–June, and then by C. tuberculata in mid-summer. Comparisons among scyphozoan species suggested that many may be restricted by low temperatures, and that global warming may benefit temperate species, but not tropical or boreal species.     

Ultrastructure of tentacles in the sipunculid worm <Emphasis Type="Italic">Thysanocardia nigra</Emphasis> Ikeda, 1904 (Sipuncula)

The ultrastructure of the tentacles was studied in the sipunculid worm Thysanocardia nigra. Flexible digitate tentacles are arranged into the dorsal and ventral tentacular crowns at the anterior end of the introvert of Th. nigra. The tentacle bears oral, lateral, and aboral rows of cilia; on the oral side, there is a longitudinal groove. Each tentacle contains two oral tentacular canals and an aboral tentacular canal. The oral side of the tentacle is covered by a simple columnar epithelium, which contains large glandular cells that secrete their products onto the apical surface of the epithelium. The lateral and aboral epithelia are composed of cuboidal and flattened cells. The tentacular canals are lined with a flattened coelomic epithelium that consists of podocytes with their processes and multiciliated cells. The tentacular canals are continuous with the radial coelomic canals of the head and constitute the terminal parts of the tentacular coelom, which shows a highly complex morphology. Five tentacular nerves and circular and longitudinal muscle bands lie in the connective tissue of the tentacle wall. Similarities and differences in the tentacle morphology between Th. nigra and other sipunculan species are discussed.Original Russian Text Copyright © 2005 by Biologiya Morya, Maiorova, Adrianov.     

Tentacular and oral-disc regeneration in the sea anemone,Aiptasia diaphana. I. Sequential morphological events in distal-end restitution

The complete regeneration of a new oral-disc and tentacles has been observed and described for Aiptasia diaphana. These structures are regenerated quite rapidly: seven to ten days at 20°C. At three days post-amputation, the new primary, secondary, and tertiary tentacle buds begin to develop in direct association with the underlying primary, secondary, and tertiary septae (respectively) of the column, suggesting that the latter organize the form of the regenerating oral-disc. Two days after amputation, the zooxanthellae of the presumptive oral disc arrange themselves into a ring which quite precisely delimits the area from which the tentacle buds will form. In spite of its suggestive proximity, this accumulation of algae plays no role in the induction of tentacle buds as was shown by studying regeneration in anemones which essentially lacked large quantities of these symbiotic algae. Cuts perpendicular to the longitudinal axis of the column result in an equal rate of tentacular regeneration around the entire circumference of the presumptive oral disc. Oblique amputations foster an asynchronous regeneration: the tentacle buds of the distal-most area of the severed column are larger and regenerate much sooner than those of the proximal region. Similar results were obtained by studying anemones which were cut perpendicular to their longitudinal axes at different levels along the column. The data suggest that an oral-aboral gradient exists concerning the time required for the initiation of tentacle budding and the rate of tentacle regeneration.     

In situ estimation of ephyrae liberated from polyps of Aurelia aurita using settling plates in Tokyo Bay, Japan

The continuous changes in the number of newly established polyps of Aurelia aurita (L.) on settling plates under natural conditions were observed from August 1998 to September 1999 in Tokyo Bay, Japan. A sharp decline in survivorship of newly settled polyps was observed within the first few days, however, survivorship of polyps settled in October increased by budding up to 399% after two months. The number of discs in each strobila varied from 1 to 6, however, most of the strobilae formed single discs. The percentage ratios of the total number of ephyrae to the initial number of polyps on settling plates were generally lower than 10%, but the highest ratio of 594.4% was estimated for the polyps settled in October. It is considered that most of the liberated ephyrae originate from the polyps settled in October in Tokyo Bay. This study suggests that the occurrence of ripe medusae with planula larvae throughout the year contributes to the success of settlement and growth of the polyp stage in Tokyo Bay.     

Novel peripheral motor neurons in the posterior tentacles of the snail responsible for local tentacle movements

Three flexor muscles of the posterior tentacles of the snail Helix pomatia have recently been described. Here, we identify their local motor neurons by following the retrograde transport of neurobiotin injected into these muscles. The mostly unipolar motor neurons (15–35 µm) are confined to the tentacle digits and send motor axons to the M2 and M3 muscles. Electron microscopy revealed small dark neurons (5–7 µm diameter) and light neurons with 12–18 (T1 type) and 18–30 µm diameters (T2 type) in the digits. The diameters of the neurobiotin-labeled neurons corresponded to the T1 type light neurons. The neuronal processes of T1 type motor neurons arborize extensively in the neuropil area of the digits and receive synaptic inputs from local neuronal elements involved in peripheral olfactory information processing. These findings support the existence of a peripheral stimulus–response pathway, consisting of olfactory stimulus—local motor neuron—motor response components, to generate local lateral movements of the tentacle tip (“quiver”). In addition, physiological results showed that each flexor muscle receives distinct central motor commands via different peritentacular nerves and common central motor commands via tentacle digits, respectively. The distal axonal segments of the common pathway can receive inputs from local interneurons in the digits modulating the motor axon activity peripherally without soma excitation. These elements constitute a local microcircuit consisting of olfactory stimulus—distal segments of central motor axons—motor response components, to induce patterned contraction movements of the tentacle. The two local microcircuits described above provide a comprehensive neuroanatomical basis of tentacle movements without the involvement of the CNS.     

Environmental factors inducing the transformation of polyp into medusae in <Emphasis Type="Italic">Aurelia aurita</Emphasis> (Scyphozoa)

The transformation of polyp into medusa is one of the most interesting processes in the life cycle of cnidarians. In the polyps of the class Scyphozoa this transformation occurs in the form of strobilation, which is the transverse fission of polyps with the formation of discoidal ephyrae. At present, the endogenous regulation of strobilation in one of scyphozoans, Aurelia aurita, is being investigated by the methods of molecular biology (Fuchs et al., 2014). However, it is still unclear which key environmental factors induce this process. The main purposes of this review are to summarize the literature data on the conditions in which strobilation in A. aurita occurs in nature and in the laboratory and to try to identify the environmental factors that are most likely to play a signaling role in strobilation.     

Immunocytochemistry of the neuromuscular systems of Loxosomella vivipara and L. parguerensis (Entoprocta: Loxosomatidae)

Little detailed information exists on the anatomy of the nervous system and the musculature of Entoprocta. Herein we describe the distribution of the neurotransmitters RFamide and serotonin as well as the myo-anatomy of adults and asexually produced budding stages of the solitary entoproct species Loxosomella vivipara and L. parguerensis using immunocytochemistry and epifluorescence as well as confocal microscopy. The development of the RFamidergic and serotonergic nervous system starts in early budding stages. In the adults, RFamide is present in the bilateral symmetric cerebral ganglion, a pair of oral nerves that innervate two pairs of nerve cell clusters in the heel of the foot, a pair of aboral nerves, the paired lateral nerves, the calyx nerves, the atrial ring nerve, the tentacle nerves, the stomach nerves, and the rectal nerves. Serotonin is only found in the cerebral ganglion, the oral nerves, and in the tentacle nerves. Some differences in the distribution of both neurotransmitters were found between L. vivipara and L. parguerensis and are most obvious in the differing number of large serotonergic perikarya associated with the oral nerves. Nerves arising from the cerebral ganglion and running in a ventral direction have not been described for Entoprocta before, and the homology of these to the ventral nerve cords of other Spiralia is considered possible. The body musculature of both Loxosomella species comprises longitudinal and diagonal muscles in the foot, the stalk, and the calyx. We found several circular muscles in the calyx. The stalk and parts of the foot and the calyx are surrounded by a fine outer layer of ring muscles. In addition to the congruent details regarding the myo-anatomy of both species, species-specific muscle structures could be revealed. The comparison of our data with recent findings of the myo-anatomy of two Loxosoma species indicates that longitudinal and diagonal body muscles, atrial ring muscles, tentacle muscles, esophageal and rectal ring muscles, as well as intestinal and anal sphincters are probably part of the ancestral entoproct muscle bauplan.     

Organization of the subumbrellar musculature in the ephyra,juvenile, and adult stages of Aurelia aurita Medusae

We used fluorescently labeled phalloidin to examine the subumbrellar musculature of the scyphozoan jellyfish Aurelia aurita in a developmental series from ephyra to adult medusa. In the ephyra, the swim musculature includes a disc‐like sheet of circular muscle, in addition to two radial bands of muscle in each of the eight ephyral arms. The radial muscle bands join with the circular muscle, and both circular and radial muscle act together during each swim contraction. As the ephyra grows into a juvenile medusa, arms tissue is resorbed as the bell tissue grows outward, so eventually, the ephyral arms disappear. During this process, the circular muscle disc also grows outward and the radial muscle bands of the arms also disappear. At this time, a marginal gap appears at the bell margin, which is devoid of circular muscle cells, but has a loose arrangement of radial muscle fibers. This marginal gap is preserved as the medusa grows, and contributes to the floppy nature of the bell margin. Radial distortions in the circular muscle layer involve muscle fibers that run in random directions, with a primarily radial orientation. These are believed to be remnants of the radial muscle of the ephyral arms, and the distortions decrease in number and extent as the medusa grows. Since the mechanics of swimming changes from drag‐based paddling in the ephyra to marginal rowing in the adult medusa, the development of the marginal gap and the presence of radial distortions should be considered in terms of this mechanical transition.     

Metabolism of 131I in relation to strobilation of Aurelia aurita L. (Scyphozoa)

The ¹³¹I isotope of iodine has been used to follow the uptake and metabolism of iodine during the process of strobilation in pre-conditioned polyps of Aurelia aurita L. Strobilating polyps accumulated free iodide from the media against a concentration gradient, the segmented portion of the polyps accumulating about three times as much as the basal portion. Almost all of the accumulated iodide appeared in the soluble portion of an acid-ethanol extract of polyp tissue as inorganic iodide. The time course of accumulation of iodine was not affected by previous exposure to either higher temperature or iodide. Inorganic iodide rather than organically bound iodine is thought to be the effective factor in the initiation of strobilation.     

Increase of CGRP Expression in Motor Endplates Within Fore and Hind Limb Muscles of the Degenerating Muscle Mouse (<Emphasis Type="Italic">Scn8a</Emphasis><Superscript><Emphasis Type="Italic">dmu</Emphasis></Superscript>)

The distribution of calcitonin gene-related peptide (CGRP) was examined in skeletal muscles of fore and hind limb as well as in oral and cranio-facial regions of the degenerating muscle (dmu) mouse, which harbours a null mutation in the voltage-gated sodium channel gene Scn8a. In limb, oral and cranio-facial muscles of wild type mice, only a few motor endplates contained CGRP-immunoreactivity. However, many CGRP-immunoreactive motor endplates appeared in the triceps brachii muscle, the biceps brachii muscle, the brachialis muscle, and the gastrocnemius muscle of dmu mice. CGRP-immunoreactive density of motor endplates in the skeletal muscles was also elevated by the mutation. In these muscles, the atrophy of muscle fibers could be detected and the density of cell nuclei in the musculature increased. In the flexor digitorum profundus muscle, the flexor digitorum superficialis muscle, and the soleus muscle as well as in oral and cranio-facial muscles, however, the distribution of CGRP-immunoreactivity was barely affected by the mutation. The morphology of muscle fibers and the distribution of cell nuclei within them were also similar in wild type and dmu mice. In the lumbar spinal cord of dmu mice, CGRP-immunoreactive density of spinal motoneurons increased. These findings suggest that the atrophic degeneration in some fore and hind limb muscles of dmu mice may increase CGRP expression in their motoneurons.     

Motor supply of the dorsal longitudinal muscles,I: homonomy and ontogeny of the motoneurones in locusts (Insecta,Caelifera)

The neural supply of the dorsal lingitudinal muscles in successive segments from the prothorax to the pregenital abdomen of adult and larval instar locusts (Locusta migratoria and Schistocerca gregaria) has been studied. Stainings have also been carried out for embryos. The whole complement consists of three muscles, of which one or both of the smaller ones degenerate in the pterothoracic segments during early imaginal life. Based on morphological criteria, several motoneurone types can be distinguished. The neural set is almost identical for all segments, independent of the general organization of each segment. At about 65% of embryogenesis, all neurone types can be identified with respect to soma position and basic features of the central branching pattern. By the end of embryogenesis, a dendritic pattern is established which resembles the adult pattern in all major aspects. The reiteration of homonomous elements suggests that they form part of the basic segmental neural Bauplan generated early in embryogenesis. This study of muscles and motoneurones forming identifiable, reiterated neuromuscular units can serve as a segmental matrix for a comparative study comprising other phylogenetic groups of the Tracheata.Abbreviations DLM dorsal longitudinal muscle - DUM dorsal unpaired median - M muscle (number) - MN motoneurone - N nerve (number)     

Neurobiology of Stomotoca. II. Pacemakers and conduction pathways

Evidence is presented for separate conduction pathways for swimming and for tentacle coordination in the marginal nerves of the jellyfish Stomotoca. The effector muscles are fired through junctions sensitive to excess Mg⁺⁺, probably represented by the neuromuscular synapses observed by electron microscopy. The swimming effector (striated muscle) fires one-to-one with nerve input signals and myoid conduction occurs. Tentacle responses (smooth muscle contractions) involve facilitation, presumably at the neuro-effector junction; responses are graded and nonpropagating. Electrical correlates of two further conducting systems using the marginal nerves have been recorded. Their functions are unknown. One, the bridge system, extends up the four radii and encircles the peduncle; the other (ring system) is confined to the margin. A fifth conducting system is inferred in the case of the pointing response and its distribution is plotted. Signals have not been obtained from it. Pointing is accompanied by a burst of muscle potentials in the radial smooth muscles and is exhibited after a lengthy latency, indicating a local pacemaker. A sixth conducting pathway is the epithelial system, which mediates crumpling, a response involving the radial muscles without pacemaker intervention. Characteristic conduction velocities and wave forms are noted for the first four systems and for epithelial pulses. All systems, except perhaps the pointing conduction system, through-conduct under excess Mg⁺⁺. Spontaneous activity patterns are described for the swimming, tentacle pulse, and ring systems. Abrupt increases in light intensity inhibit spontaneous activity, sudden decreases augmenting it. In the absence of specialized photoreceptors, light is presumed to act directly on central neurons. Epithelial pulses inhibit swimming, apparently by blocking the generation or conduction of the primary nervous events. This observation, taken in conjunction with evidence of feedback inhibition of the primary swimming system by the cells it fires, is discussed in relation to possible mechanisms whereby the output of nerve cells might be altered by activity in the excitable epithelial cells which envelop them.     

Effects of climate warming on strobilation and ephyra production of North Sea scyphozoan jellyfish

Recent studies have correlated fluctuations in jellyfish abundances with climatic changes, leading to speculation that the warming trend in the North Sea will affect the strobilation activity of Scyphozoa. The present study provides long-term data (10–22 months) on temperature effects on the species Aurelia aurita, Cyanea capillata, Cyanea lamarckii and Chrysaora hysoscella. Strobilation at current winter temperature (5°C) in the German Bight was compared to strobilation at warmer winter temperatures. Simulated winter temperature of 10°C had several positive effects on strobilation, as compared to 5°C: 1. A longer strobilation period or higher ephyra production per polyp in A. aurita, C. lamarckii and Ch. hysoscella; 2. Higher percentages of polyps strobilating in A. aurita and Ch. hysoscella; 3. More ephyrae per strobila in C. capillata and C. lamarckii; 4. A shorter strobilation duration in C. capillata and C. lamarckii. Cold winter temperatures of 5°C promoted strobilation in C. capillata, but inhibited strobilation in A. aurita and reduced ephyra production in C. lamarckii and Ch. hysoscella. These results suggest that climate warming will benefit A. aurita, but not cold-water C. capillata. The distributions of C. lamarckii and Ch. hysoscella probably could expand to the north.     

Three-dimensional reconstruction of the musculature of Cossura pygodactylata Jones, 1956 (Annelida: Cossuridae)

The musculature of adult specimens of Cossura pygodactylata was studied by means of F-actin labelling and confocal laser scanning microscopy (CLSM). Their body wall is comprised of five longitudinal muscle bands: two dorsal, two ventral and one ventromedial. Complete circular fibres are found only in the abdominal region, and they are developed only on the border of the segments. Thoracic and posterior body regions contain only transverse fibres ending near the ventral longitudinal bands. Almost-complete rings of transverse muscles, with gaps on the dorsal and ventral sides, surround the terminal part of the pygidium. Four longitudinal bands go to the middle of the prostomium and 5–14 paired dorso-ventral muscle fibres arise in its distal part. Each buccal tentacle contains one thick and two thin longitudinal muscle filaments; thick muscle fibres from all tentacles merge, forming left and right tentacle protractors rooted in the dorsal longitudinal bands of the body wall. The circumbuccal complex includes well-developed upper and lower lips. These lips contain an outer layer of transverse fibres, and the lower lip also contains inner oblique muscles going to the dorsal longitudinal bands. The branchial filament contains two longitudinal muscle fibres that do not connect with the body musculature. The parapodial complex includes strong intersegmental and segmental oblique muscles in the thoracic region only; chaetal retractors, protractors and muscles of the body wall are present in all body regions. Muscle fibres are developed in the dorsal and ventral mesenteries. One semi-circular fibre is developed on the border of each segment and is most likely embedded in the dissepiment. The intestine has thin circular fibres along its full length. The dorsal blood vessel has strong muscle fibres that cover its anterior part, which is called the heart. It consists of short longitudinal elements forming regular rings and inner partitions. The musculature of C. pygodactylata includes some elements that are homologous with similar muscular components in other polychaetes (i.e., the body wall and most parapodial muscles) and several unique features, mostly at the anterior end.     

Peptidergic motoneurons in the buccal ganglia of Aplysia californica Immunocytochemical,morphological, and physiological characterizations

Summary We used physiological recordings, intracellular dye injections and immunocytochemistry to further identify and characterize neurons in the buccal ganglia of Aplysia calif ornica expressing Small Cardioactive Peptide-like immunoreactivity (SCP-LI). Neurons were identified based upon soma size and position, input from premotor cells B4 and B5, axonal projections, muscle innervation patterns, and neuromuscular synaptic properties. SCP-LI was observed in several large ventral neurons including B6, B7, B9, B10, and B11, groups of s1 and s2 cluster cells, at least one cell located at a branch point of buccal nerve n2, and the previously characterized neurons B1, B2 and B15.B6, B7, B9, B10 and B11 are motoneurons to intrinsic muscles of the buccal mass, each displaying a unique innervation pattern and neuromuscular plasticity. Combined, these motoneurons innervate all major intrinsic buccal muscles (I1/I3, I2, I4, I5, I6). Correspondingly, SCP-LI processes were observed on all of these muscles. Innervation of multiple nonhomologous buccal muscles by individual motoneurons having extremely plastic neuromuscular synapses, represents a unique form of neuromuscular organization which is prevalent in this system. Our results show numerous SCPergic buccal motoneurons with widespread ganglionic processes and buccal muscle innervation, and support extensive use of SCPs in the control of feeding musculature.Abbreviations SCP-LI small cardioactive peptide-like immunoreactivity - PSC postsynaptic current - EPSP excitatory postsynaptic potential - IPSP inhibitory postsynaptic potential - FI facilitation index - TMR time to maximal response     

Functional design of tentacles in squid: linking sarcomere ultrastructure to gross morphological dynamics

This paper offers a quantitative analysis of tentacle extension in squid that integrates several levels of structural organization. The muscular stalks of the two tentacles of squid are rapidly elongated by 70 per cent of resting length during prey capture. A typical duration of the extension is 30 ms in Loligo pealei (with a contracted tentacle length of 93 mm and a strike distance of about 37 mm). In a successful strike, the terminal clubs hit the prey and attach to it via arrays of suckers.A forward dynamics model is proposed for the extension of the tentacular stalk and the forward motion of the terminal club. The stalk is modelled as a longitudinal array of thin muscular discs with extensor muscle fibres oriented parallel to the disc planes. As a disc contracts radially, it lengthens because its volume is constant. The equations of motion for the linked system of discs were formulated and solved numerically. The inputs of the model are the dimensions of the tentacle, passive and active muscle properties such as Hill''s force–velocity relationship, myofilament lengths and activation of the muscle fibres. The model predicts the changing geometry of the tentacle, the pressure and stress distribution inside the tentacle and the velocity and kinetic energy distribution of the stalk and club. These predictions are in agreement with kinematic observations from high-speed films of prey capture. The model demonstrates also that the unusually short myosin filaments (reported range 0.5–0.9 micrometre) that characterize the extensor muscles are necessary for the observed extension performance. Myosin filament lengths typical for vertebrate sarcomeres (1.58 micrometre) would lead to a significant reduction in performance. In addition, the model predicts that, to maximize peak velocity of the terminal club, the myosin filaments should be longer at the base and shorter at the tip of the stalk (0.97 micrometre at the base and 0.50 micrometre at the tip for the tentacle size above). This results from differences in dynamic loading along the stalk. Finally, the model allows exploration of the effects of changes in the dimensions and mass of the tentacle and intrinsic speed of the myofilaments on the optimum myosin filament lengths.     

Composition of Bacterial Communities Associated with Aurelia aurita Changes with Compartment,Life Stage,and Population

The scyphozoan Aurelia aurita is recognized as a key player in marine ecosystems and a driver of ecosystem change. It is thus intensely studied to address ecological questions, although its associations with microorganisms remain so far undescribed. In the present study, the microbiota associated with A. aurita was visualized with fluorescence in situ hybridization (FISH) analysis, and community structure was analyzed with respect to different life stages, compartments, and populations of A. aurita by 16S rRNA gene amplicon sequencing. We demonstrate that the composition of the A. aurita microbiota is generally highly distinct from the composition of communities present in ambient water. Comparison of microbial communities from different developmental stages reveals evidence for life stage-specific community patterns. Significant restructuring of the microbiota during strobilation from benthic polyp to planktonic life stages is present, arguing for a restructuring during the course of metamorphosis. Furthermore, the microbiota present in different compartments of the adult medusa (exumbrella mucus and gastric cavity) display significant differences, indicating body part-specific colonization. A novel Mycoplasma strain was identified in both compartment-specific microbiota and is most likely present inside the epithelium as indicated by FISH analysis of polyps, indicating potential endosymbiosis. Finally, comparison of polyps of different populations kept under the same controlled laboratory conditions in the same ambient water showed population-specific community patterns, most likely due the genetic background of the host. In conclusion, the presented data indicate that the associated microbiota of A. aurita may play important functional roles, e.g., during the life cycle.     

Attraction of Aurelia and Aequorea to prey

Previously it has been assumed that medusae make random contact with their prey. Medusae were tested in a flow-through aquarium with inflow at each end and a central outflow. Aurelia aurita and Aequorea victoria were attracted to either end of the chamber if Artemia prey were present in a screened compartment. A. aurita was also shown to be attracted to water conditioned by Artemia, and to ammonium chloride added to one or other of the inflow currents.