Modulation of the feeding system by a radular mechanosensory neuron in the terrestrial slug,Incilaria fruhstorferi

We investigated the modulatory role of a radular mechanoreceptor (RM) in the feeding system of Incilaria. RM spiking induced by current injection evoked several cycles of rhythmic buccal motor activity in quiescent preparations, and this effect was also observed in preparations lacking the cerebral ganglia. The evoked rhythmic activity included sequential activation of the inframedian radular tensor, the supramedian radular tensor, and the buccal sphincter muscles in that order.In addition to the generation of rhythmic motor activity, RM spiking enhanced tonic activities in buccal nerve 1 as well as in the cerebrobuccal connective, showing a wide excitatory effect on buccal neurons. The excitatory effect was further examined in the supramedian radular tensor motoneuron. RM spiking evoked biphasic depolarization in the tensor motoneuron consisting of fast excitatory postsynaptic potentials and prolonged depolarization lasting after termination of RM spiking. These depolarizations also occurred in high divalent cation saline, suggesting that they were both monosynaptic.When RM spiking was evoked in the fictive rasp phase during food-induced buccal motor rhythm, the activity of the supramedian radular tensor muscle showed the greatest enhancement of the three muscles tested, while the rate of ongoing rhythmic motor activity showed no increase.Abbreviations CPG central pattern generator - EPSP excitatory postsynaptic potential - RBMA rhythmic buccal motor activity - RM radular mechanosensory neuron - SMT supramedian radular tensor neuron     

Is Doris georgiensis García et al. 1993 a distinct species of dorid nudibranch?

The reproductive system and radular morphology of several specimens of Doris collected in the Antarctic Ocean were examined in an attempt to clarify the taxonomic status of Doris kerguelenensis and its possible synonym Doris georgiensis. A comparative analysis of the samples was conducted to find correlations between the anatomy of the bursa copulatrix and variations in the radular morphology and external features of these two species. Some consistent differences were found, suggesting the possibility of the existence of two distinct species, but further investigations are necessary to substantiate these conclusions.     

Experimental and comparative morphology of radula renewal in pulmonates (Mollusca,Gastropoda)

Summary The continuous renewal of the pulmonate radula and the histology and regeneration of its concomitant epithelia were studied by light and electron microscopy, autoradiography and electron microprobe analysis. The two species investigated show histological differences and the results were compared with those of a preceding study on a prosobranch radula. The radula is an intricate cuticular structure of the foregut. Only the fully grown part, which is active during feeding, lies in the buccal cavity while it is constantly renewed by the coordinated cooperation of specialized cells forming the radular sheath. The end of the sheath is occupied by cells which produce the organic matrix of the radula. In taeniogloss prosobranchs, seven multicellular cushions of small odontoblasts lie at the end of the sheath and produce the seven teeth of each cross-row. In pulmonates, the multidenticular radula is generated by numerous groups of a few voluminuous cells. Despite these histological differences, prosobranchs and pulmonates generate the radula matrix by microvilli, cytoplasmatic protrusions and apocrine secretions. The epithelia of the radular sheath contribute to the transport, tanning and mineralization of the radula. The concomitant epithelia are replaced in limited proliferation zones at the end of the radular sheath and their cells migrate anteriorly to the buccal cavity. The ultrastructure of the sheath cells and the alterations which they undergo in connection with their functions are discussed. The proliferation zone of the superior epithelium is strictly confined and the cells move together with the radula forward. In prosobranchs, the cells of the superior epithelium begin to degenerate in the middle of the radular sheath and the entire epithelium is simply extruded into the buccal cavity. In pulmonates, the opening of the radular sheath is closed by the cuticular collostylar hood which is generated by a distinct epithelium which is proved to be stationary. When leaving the proliferation zone, the superior epithelium differentiates into supporting cells and mineralizing cells; the latter cause the hardening of the radular teeth and already degenerate in the middle of the sheath. The whole superior epithelium degenerates at the border to the collostylar hood-epithelium. In Lymnaea the degeneration zone is strictly confined whereas in Cepaea the collostylar hood and its generating epithelium extend into the radular sheath and the degeneration zone ranges over a distance of 3–5 rows of teeth. The proliferation zone of the inferior epithelium extends over the posterior half of the radular sheath, but the replacement rate is much lower than in the superior epithelium. Although the inferior epithelium carries the radula, it migrates slower than the radula. Obviously the radula has to be transported actively by apical protrusions of the cells, which penetrate into the radular membrane. At the opening of the radular sheath the inferior epithelium generates the adhesive layer and degenerates. During feeding, the adhesive layer has to maintain the firm mechanical connection between radula and distal radular epithelium. Autoradiographic experiments demonstrate that the distal radular epithelium is stationary. Nevertheless, the radula is known to advance to its degeneration zone. Special attention is paid to this problem. We strongly suspect that the transport of the adhesive layer and the radula is based on pseudopodial movements of apical protrusions characteristic for the distal radular epithelium. These protrusions interdigitate with the lower face of the adhesive layer. The mechanical connection has to be maintained and so the respective structures (tonofilaments and hemi-desmosomes) have to be continually renewed. This needs a high amount of energy and obviously results in the conspicuous concentration of mitochondria near the apical surface.Abbreviations al adhesive layer - ax axon - bc buccal cavity - bce buccal cavity epithelium - bl basal layer - bla basal labyrinth - bm basal membrane - bp basal plate - bpc basal plate cell - c cilia - ch collostylar hood - che collostylar hood-epithelium - cl cuticular layer - col collostyle - cr cell remnant - cts connective tissue sheath - d desmosome - dl upper layer - dre distal radular epithelium - dz degeneration zone - fe front edge - g granula - gol dictyosome - hd hemidesmosome - hl haemolymph - ie inferior epithelium - j jaw - ma tooth matrix - mc mineralizing cell - mem membranoblast - mfb microfibrills - mfl microfilaments - mgb multigranular body - mi mitochondria - mit mitosis - ml middle layer - mt microtubuli - mv microvilli - mw membrane whirl - n nucleus - nc necrotic cluster - nf nerve fibres - nsg neurosecretory granula - o odontophor - od odontoblast - odg odontoblast group - pod pre-odontoblast - rb residual body - rer rough endoplasmatic reticulum - rm radular membrane - rt radula teeth - sc supporting cell - se superior epithelium - sj septate junction - sro subradular organ - ss secretion substance - tf tonofilaments - tsm supramedian tensor muscle - tw terminal web - v vacuole - ves vesicle     

Comparative buccal anatomy in Helisoma (mollusca,pulmonata, basommatophora)

Dissections were performed to document buccal anatomy in three species of the pulmonate genus Helisoma Swainson, 1840. The 28 muscles which are responsible for radular feeding in these animals are organized in three concentric and integrated envelopes. The deepest of these includes muscles which manipulate the radula about the odontophoral cartilage. Elements of the middle envelope direct movements of the cartilage within the buccal cavity, and muscles of the outer envelope control movements of the buccal mass within the cephalic haemocoel. Motion analysis by videomicrography showed that muscles of the middle and outer envelopes contribute to the action of radular feeding by acting as antagonists to other muscles and to hydrostatic elements of the buccal apparatus. Observations of radular dentition showed that although each of the three species examined has a unique radula, especially with regard to the specific details of tooth shape, all resemble a radula characteristic of the Planorbidae with regard to other, more general, aspects of ribbon architecture.     

The relation between excitation-contraction coupling and fine structure of a molluscan muscle,the radular retractor of the whelk,Buccinum undatum

The Buccinum radula is of the rachiglossate type with two outer rows of fierce hook-like attack teeth and a medial row of straight sharp-pointed shredding teeth. Individual cells of the radular retractor muscle are 10–12 m in diameter and separated at the closest by gaps of only 40 nm, providing areas of potential electrical contact. The cell membranes are heavily invested with long finger-like invaginations, associated with sarcoplasmic reticular cisternae, and surface caveolae; the latter are associated with the numerous dense body membrane attachment plaques found in this muscle. The radular retractor muscle possesses a significant sarcoplasmic reticulum of peripheral cisternae and deeper vesicles associated with mitochondria. The surface caveolae may result from myofilament force exerted via attachment plaques at the cell membrane, while deeper invaginations may constitute a rudimentary transverse tubular system to relay surface depolarization to associated sarcoplasmic reticular cisternae inducing calcium release to effect excitation-contraction coupling. The radular retractor muscle possesses the usual thick paramyosin and thin actin myofilaments, the latter associated with dense bodies and attachment plaques presumably to transduce force to the cell membrane. The mitochondria are unusually large and packed into dense central clusters surrounded by large deposits of glycogen granules. The nerve endings on the radular retractor muscle fibres show four different types of transmitter vesicle, presumably related to the four kinds of agonist action in this muscle, cholinergic, serotonergic, peptidergic and purinergic. All nerve endings have mixed vesicle populations, clear evidence of co-transmission. In this muscle we see a modification of usual smooth muscle structure to effect fast sustained contractions, an ultrastructural configuration functionally designed for the muscle's central role in the feeding cycle.Abbreviations ABRM anterior byssus retractor muscle - EC coupling excitation-contraction coupling - RP radular protractor muscle - RR radular retractor muscle - SR sarcoplasmic reticulum - T-system transverse tubular system     

Effects of body size and water temperature on grazing rates of four intertidal gastropods

Abstract Rates of radular activity were measured in four species of Australian gastropods. The species were Austrocochlea constricta, Bembicium nanum, Cellana tramoserica, and Nerita atramentosa. Work was done in Botany Bay at Cape Banks, NSW, Australia from September 1989 to June 1990. A hydrophone was used to record radular raspings of snails in situ. Averages based on all observations showed Cellana had the fastest rate with 80 rasps/min, and was followed by Austrocochlea (71 rasps/min), Bembicium (57), and Nerita (39). Faster rates were associated with warmer water temperature and smaller body sizes in all species except Bembicium. The potential for these differences in radular activity affecting competitive interactions is discussed.     

Integrative systematics of northern and Arctic nudibranchs of the genus Dendronotus (Mollusca,Gastropoda), with descriptions of three new species

The taxonomy of common northern nudibranch molluscs of the genus Dendronotus in the vast cold regions of Eurasia remains largely unknown. Abundant material collected in many localities from the Barents Sea, via the Arctic region, to the north‐west Pacific was analysed for the first time. An integrated approach combining morphological and ontogenetic data with molecular four‐gene (COI, 16S, H3, and 28S) analysis reveals seven species, including three previously undescribed. Dendronotus frondosus (Ascanius, 1774) and Dendronotus dalli Bergh, 1879 were commonly considered as amphiboreal species; however, according to this study they are restricted to the North Atlantic and the North Pacific, respectively. In the north‐west Pacific two new species were discovered, D endronotus kamchaticus sp. nov. and D endronotus kalikal sp. nov. , that are externally similar to D. frondosus, but that show significant distance according to molecular analysis and are considerably different in radular morphology. In the North Atlantic a new species D endronotus niveus sp. nov. , sibling to North Pacific D. dalli, is revealed. The separate status of North Atlantic Dendronotus lacteus (Thompson, 1840) is confirmed, including considerable range extension. The essential similarity of early ontogenetic stages of radular development common for species with disparate adult radular morphology (such as D. frondosus and D. dalli) is shown, and its importance for taxonomy is discussed. © 2015 The Linnean Society of London     

Diversity of mechanical responses and their possible underlying mechanisms in the proboscis muscles ofBusycon canaliculatum

Summary Mechanical responses of the radular protractor and retractor, the odontophore retractor and the radular sac muscles ofBusycon canaliculatum were compared. The radular protractor responded to both ACh and high K salines with similar slow, smooth contractures showing no evidence of fast twitch activity. The radular sac, odontophore retractor, and radular retractor muscles responded to low K salines with bursts of fast twitches at a mechanical threshold below that for responses in the radular protractor. With high K salines these three muscles showed inactivation of fast twitch activity and replacement by slow maintained tonic force. With rare exceptions, the ACh responses of all four muscles consisted of slow, maintained tonic contractures with no fast twitch activity, although individual muscles differed in their ACh sensitivity. A scheme is presented to explain the mechanical modus operandi of this complex organ by the co-operative actions of these four physiologically diverse muscles. It is proposed that fast twitch responses depend upon the activity of fast transient Ca channels showing strong voltage sensitivity and ready voltage inactivation. It is proposed that maintained tonic contractures in all the muscles depends upon the activity of slow long-lasting voltage-dependent Ca channels which only open with substantial membrane depolarization. It is suggested that K-induced and ACh-induced responses may activate a similar cellular Ca pool but by different membrane transduction routes.     

Morphobiochemical adaptations to littoral habitation and feeding in mediterranean <Emphasis Type="Italic">Aplysia depilans</Emphasis> (Gmelin, 1791) (Opistobranchia,Tectibranchia)

Features of the external structure, behavior, nourishment, ponderal index of viscera, and quantitative content of myoglobin in radular and stomach muscles of Aplysia depilans are analyzed in the article.     

The radula of the Late Cretaceous scaphitid ammonite Rhaeboceras halli (Meek and Hayden, 1856)

Abstract: Radular teeth occur between the jaws in two specimens of the Late Cretaceous scaphitid ammonite Rhaeboceras halli (Meek and Hayden, 1856) from the Western Interior of the United States. The detailed morphology of the teeth has been revealed by propagation phase contrast X‐ray synchrotron microtomography. Each row of the radula of R. halli consists of a total of seven teeth (a central rachidian, two pairs of lateral and one pair of marginal teeth), as in other known ammonoid radulae, although the central tooth could not be confirmed in the specimens examined. The lateral teeth are multicuspid and robust, and the marginal teeth are long (4.6 mm) and slender. In overall morphology, the heterodont and ctenoglossan radula of R. halli is similar that of Jurassic and Cretaceous ammonites with the same aptychus‐type lower jaw, that is, the Aptychophora. This discovery reveals the range of variation in radular morphology, which could be related to ecological or phylogenetic factors. It also invalidates the hypothesis that the hook‐like structures in R. halli previously described are radular elements.     

Radula formation in two species of Conoidea (Gastropoda)

The radula is the basic feeding structure in gastropod molluscs and exhibits great morphological diversity that reflects the exceptional anatomical and ecological diversity occurring in these animals. This uniquely molluscan structure is formed in the blind end of the radular sac by specialized cells (membranoblasts and odontoblasts). Secretion type, and the number and shape of the odontoblasts that form each tooth characterize the mode of radula formation. These characteristics vary in different groups of gastropods. Elucidation of this diversity is key to identifying the main patterns of radula formation in Gastropoda. Of particular interest would be a phylogenetically closely related group that is characterized by high variability of the radula. One such group is the large monophyletic superfamily Conoidea, the radula of which is highly variable and may consist of the radular membrane with five teeth per row, or the radular membrane with only two or three teeth per row, or even just two harpoon-like teeth per row without a radular membrane. We studied the radulae of two species of Conoidea (Clavus maestratii Kilburn, Fedosov & Kantor, 2014 [Drilliidae] and, Lophiotoma acuta (Perry, 1811) [Turridae]) using light and electron microscopy. Based on these data and previous studies, we identify the general patterns of the radula formation for all Conoidea: the dorsolateral position of two groups of odontoblasts, uniform size, and shape of odontoblasts, folding of the radula in the radular sac regardless of the radula configuration. The morphology of the subradular epithelium is most likely adaptive to the radula type.     

Radular mechanosensory neuron in the buccal ganglia of the terrestrial slug,Incilaria fruhstorferi

A radular mechanosensory neuron, RM, was identified in the buccal ganglia of Incilaria fruhstorferi. Fine neurites ramified bilaterally in the buccal ganglia, and main neurites entered the subradular epithelium via buccal nerve 3 (n3). When the radula was distorted by bending, RM produced an afferent spike which was preceded by an axonic spike recorded at n3. The response of RM to radular distortion was observed even in the absence of Ca²⁺, which drastically suppressed chemical synaptic interactions. Therefore, RM was concluded to be a primary radular mechanoreceptor.During rhythmic buccal motor activity induced by food or electrical stimulation of the cerebrobuccal connective, RM received excitatory input during the radular retraction phase. In the isolated buccal ganglia connected to the radula via n3s, the afferent spike, which had been evoked by electrical stimulation of the subradular epithelium, was broadened with the phasic excitatory input. Since the afferent spike was also broadened by current injection into the soma, depolarization due to the phasic input may have produced the spike broadening.Spike broadening was also observed during repetitive firing evoked by current injection. The amplitude of the excitatory postsynaptic potential in a follower neuron increased depending on the spike broadening of RM.Abbreviations CBC cerebrobuccal connective - EPSP excitatory postsynaptic potential - n1,n3 buccal nerves 1 and 3 - RBMA rhythmic buccal motor activity - RM radular mechanosensory neuron - SMT supramedian radular tensor neuron     

Degradation of the radula in the snails Biomphalaria glabrata say and Limnaea stagnalis L. (Gastropoda,Pulmonata)

Summary The radula of snails is formed at the posterior end of the radular gland or pocket, and degraded at the same rate at its anterior end. Degradation is due to different secretory activities of the inferior epithelium of the radular gland. Its secretions seem to degrade enzymatically the matrix of the radular membrane and basal plates of teeth, leaving only chitin containing microfibres and degradation products. The sclerotized parts of the teeth remain unchanged, but as they are now only loosely connected with the radular membrane. they are torn off easily during feeding movements. The rest of the degraded and frayed radular membrane and the subradular membrane are also lost by abrasion during feeding. The cells of the inferior epithelium are connected with each other by septate desmosomes and an elaborate system of deep lateral interdigitation which may provide tensile strength. Extrusion of degraded cells of the inferior epithelium into the subradular membrane takes place, although the thick basal lamina forms a continuous sheath which is closely adjoined to the basal parts of the inferior epithelium. Nerve fibres containing vesicles with electron dense neurosecretory material (deduced from the diameter of 200–250 nm) are attached to this sheath or penetrate into it; they may be involved in the regulation of production and degradation processes during radula replacement. Problems of the forward transport of radula and inferior epithelium are discussed.     

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

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

Electron microscopic studies on radular tooth formation in the snails Helix pomatia L. and Limax flavus L. (Pulmonata,Stylommatophora)

The radular teeth are secreted at the posterior end of the radular gland and move slowly towards the buccal cavity where they start to function. Helix pomatia and Limax flavus were examined to determine whether the newly formed teeth already show their definite species specific shape, or whether they are gradually finished and moulded in the radular gland. Scanning electron micrographs of Helix pomatia show that teeth are secreted in the odontoblast region in their final form. Their surface is still uneven at the outset; the same is true for the newest teeth of Limax flavus. Older teeth ready for use have a smooth surface. This change seems to be brought about by secretory activity of the superior epithelium of the radular sac. Air-dried radulae, previously isolated by KOH maceration, show considerable artefacts at their posterior end. Maceration leads to shrinking of the newest teeth, but does not change their contours. The newly secreted but as yet unhardened teeth become greatly deformed during the drying process.     

Some adaptations of <Emphasis Type="Italic">Monodonta turbinata</Emphasis> (Born, 1780) (Gastropoda,Prosobranchia, Trochidae) to feeding and habitation in the littoral zone

The basic morphological, ethological, and physiological-biochemical adaptations of Monodonta turbinata to survival in the littoral zone were investigated in this work. Quantitative estimation of myoglobin content in radular tissues of mollusks inhabiting the Mediterranean Sea Basin has been carried out.     

两种石磺齿舌形态差异分析

显微观察了瘤背石磺(Onchidiumstruma)和石磺(O. verruculatum)齿舌的形态结构。运用差异系数法对两种石磺齿舌参数进行比较分析。利用SPSS10.0对瘤背石磺、石磺齿舌参数(齿舌长、齿舌头宽、齿舌中宽、齿舌尾宽、横列数、每排最少齿片数和每排最多齿片数)与个体参数(体长、体宽、体高、足长、足宽和体重)作回归分析。结果表明,两种石磺齿舌都很发达,外观呈长统靴状;齿片排成许多横列,每一横列均有中央齿一枚,侧齿若干无缘齿;两种石磺的齿舌头宽、齿舌中宽和齿舌尾宽差异极显著,但差异系数小于1.28,认为两种石磺的齿片形态存在明显的种间差异,但齿舌参数不适合作为石磺属贝类的分类依据;瘤背石磺的体宽和石磺的体重在评估各自齿舌生物学性状方面起到比较重要的作用。     

Functional analysis of morphological and biochemical parameters in the gastropod <Emphasis Type="Italic">Phalium undulatum</Emphasis> (Gmelin, 1791) (Cassidae,Mollusca)

Phalium undulatum is a predatory snail that feeds on sea urchins by boring through their shells. Weight parameters of individual components of the radular apparatus and some internal organs and the contents of tissue hemoglobin in the radular tissues and heart muscle of this mollusk are analyzed.     

Morphological and Molecular Resolution of a Putative Cryptic Species Complex: a Case Study of Notoacmea Fascicularis (Menke, 1851) (Gastropoda: Patellogastropoda)

Evidence that Notoacmea fascicularis (Menke, 1851) is a complexof at least two distinct taxa of species rank is ambiguous.A discriminant function analysis of conchological data showsa weak geographic effect, while radular morphology clearly delineatestwo sympatric groups with rare intermediates. Lastly, moleculardata (mt cytochrome c oxidase subunit I) suggests a single speciesand a geographic effect. We consider N. fascicularis to be a singletaxon, variable for radular lateral tooth morphology. In thepast these two different radular morphologies would be indicativeof generic rank. Our knowledge of the intraspecific variability ofmost gastropod characters is poor, and this makes specific identificationsor groupings based on single character systems such as the radulaprecarious. Adequate sampling and evaluation of population-levelcharacter states (conchological, anatomical and molecular) isneeded to identify as well as falsify cryptic species complexes. (Received 28 August 1997; accepted 6 May 1998)