Activity patterns in radular retractor motoneurones of the snail,Planorbarius

Brace, R. C.; Quicke, Donald L. J.

doi:10.1007/bf00605744

Cited by 8 publications

(1 citation statement)

References 25 publications

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“…Its activity undoubtedly forces the odontophoral tip posterodorsally during retrac tion, as in other pulmonates (Grampton 1973). This conclusion is substantiated by the feature that, in Planorbarius c o r n e u s , those motoneurons supplying the supralateral radular ret (see below) which also innervate part of the buccal-sphincter, are primarily active during retraction (Brace & Quicke 1981).…”

Section: (I) Suprapallial Blood Systemmentioning

confidence: 88%

Observations on the morphology and behaviour ofChilina fluctuosaGray (Chilinidae), with a discussion on the early evolution of pulmonate gastropods

Brace

1983

Phil. Trans. R. Soc. Lond. B

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An account is provided of (i) the general morphology, (ii) the vascular, nervous and feeding systems, and (iii) aspects of the behaviour of a representative species of the pulmonate genus Chilina . Examination of this genus has aided in understanding the pattern of early evolution of freshwater pulmonates from their marine prosobranch ancestors and of their divergence from opisthobranchs. The gross morphology of Chilina is adapted to ploughing through the surface layers of soft substrata. Although C. fluctuosa was found on rocks, it was nevertheless capable of burrowing into sand, using a stereotyped digging cycle. Streamlining to facilitate burrowing was achieved by nuchal shortening and by a ‘detorsion’ of the mantle complex as in opisthobranchs. The nuchal shortening incurred loss of a major vascular pathway which, in monotocardian prosobranchs, drains the head-foot. ‘Detorsion’, however, provided a substitute which incorporates the anterior roof of the mantle cavity where, in Chilina , the precursor of the rich pulmonary plexus characteristic of later pulmonates may be discerned. The suprapallalial vascular system is described in detail. In contrast, it is apparent that increased reliance on burrowing in opisthobranchs brought about loss of the anterior region of the mantle cavity, and thus any potential for development of a plexus in that region. Enclosure of the mantle cavity, which clearly pre-adapted the mantle complex to function also as a ‘lung’, was necessary to reduce clogging of the mantle cavity by particulate material. Only water is held in the cavity of Chilina flutuosa , whose habitat is rivers, but both air and water may be held in the mantle complex of other species found in Chile. The nervous system is extremely similar to that of the primitive opisthrobranch Acteon , but the posterior section of the visceral loop is shorter owing to greater nuchal reduction. The loop is uncrossed, though the supraoesophageal ganglion lies only a little right of the suboesophageal ganglion. The musculature of the buccal mass is extremely similar to that of Lymnaea and Planorbarius , and is designed for moving and tensing a broad radular ribbon. It is argued that the buccal morphology characteristic of these snails evolved to manipulate quantities of particulate material during the early infaunal phase, and only later was used to great effect in both microphagous and macrophagous feeding. Collectively, the observations made on C. flluctuosa (and also on estuarine species found in Chile) support the contention that the Basommatophora invaded freshwater habitats via estuarine niches. Continuity during this progression was apparently provided by soft substrata, and probably by diatoms as a food source. Previous arguments purporting a terrestrial or semi-terrestrial origin for the limnic basommatophorans are refuted.

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Section: (I) Suprapallial Blood Systemmentioning

confidence: 88%

Observations on the morphology and behaviour ofChilina fluctuosaGray (Chilinidae), with a discussion on the early evolution of pulmonate gastropods

Brace

1983

Phil. Trans. R. Soc. Lond. B

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

Smith

1990

Journal of Morphology

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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.

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Control of feeding movements in the freshwater snail Planorbis corneus

YuI

et al. 1988

Exp Brain Res

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(1) The buccal mass of the freshwater snail Planorbis corneus, dissected together with the buccal ganglia, performs rhythmic feeding movements. Radula movements and the electrical activity in various nerves of buccal ganglia were recorded in such a preparation. The cycle of radula movements consisted of three phases: quiescence (Q), protraction (P) and retraction (R). The activity in the radular nerve was observed mainly in the P-phase and that in the dorsobuccal nerve, largely in the R-phase. (2) Isolated buccal ganglia were capable of generating a feeding rhythm, the activity in buccal nerves being similar to that observed in the buccal mass-buccal ganglion preparation, i.e., a burst in the radular nerve preceded a burst in the dorsobuccal nerve. The activity of neurons in isolated buccal ganglia during generation of the feeding rhythm has been studied with intracellular microelectrodes. About 10% of ganglion neurons exhibited periodic activity related to the feeding rhythm ("rhythmic" neurons). (3) Rhythmic neurons have been divided into 7 groups according to the phase of their activity and to the characteristics of slow oscillations of the membrane potential during the feeding cycle. Group 1 neurons revealed a gradual increase of depolarization during the Q- and P-phases. In subgroup 1e neurons, spike discharges began in the Q-phase, while in subgroup 1d neurons activity started in the P-phase. During the R-phase, group 1 neurons were strongly hyperpolarized, and their discharges terminated. In group 2 neurons, small depolarization gradually increased during the Q- and P-phases. Then, in the R-phase, a large (20-50 mV) rectangular wave of depolarization arose with superimposed high-frequency oscillations. Group 3 neurons exhibited an excitatory postsynaptic potential (EPSP) in the P-phase and inhibitory postsynaptic potential (IPSP) in the R-phase. The neurons of group 4 revealed two EPSPs: a small one in the P-phase and a larger one in the R-phase. Group 5 neurons exhibited an EPSP in the P-phase, those of group 7 - an IPSP in the R-phase, and those of group 9 - IPSPs in the P- and R-phases. Neurons within each of the groups 1, 2 and 4 were electrically coupled, and in addition, there were also electrical connections between neurons of groups 2 and 4. (4) Data are presented showing that neurons of groups 1 and 2 are the main source of postsynaptic potentials in rhythmic neurons in the P-phase and in the R-phase of the cycle, respectively.

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Activity patterns in radular retractor motoneurones of the snail,Planorbarius

Cited by 8 publications

References 25 publications

Observations on the morphology and behaviour ofChilina fluctuosaGray (Chilinidae), with a discussion on the early evolution of pulmonate gastropods

Observations on the morphology and behaviour ofChilina fluctuosaGray (Chilinidae), with a discussion on the early evolution of pulmonate gastropods

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

Control of feeding movements in the freshwater snail Planorbis corneus

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