An ultrastructural study of the musculature of the pond snail Lymnaea stagnalis (L.)

Abstract

The ultrastructure of the musculature of Lymnaea stagnalis was studied. Each of the six muscle systems of the body wall, previously distinguished in an anatomical study, has its own type of smooth muscle, characterised by the size and number of the myofilaments, number of mitochondria and distribution of smooth endoplasmic reticulum. The visceral musculature comprises both smooth and striated muscle. Cross-striated muscle is found in the heart and proximal aorta, obliquely striated muscle in the buccal mass, gizzard and vas deferens. Myofibroblasts and myoendothelial cells were also distinguished. On the basis of the observations it is concluded that striated muscles in L. stagnalis contract and relax more rapidly and have a higher endurance than smooth muscles, but that the latter can contract over a wider range. Among smooth muscles the head retractor muscle contracts most rapidly, the shell muscle is most powerful and the diagonal muscle is slow to contract but has a relatively high endurance. The latter muscle, together with the horizontal foot muscle, plays a major role in maintenance of the hydrostatic skeleton. A model for the organisation of the smooth muscles is deduced from the ultrastructural observations. It implies that the myosin-paramyosin filaments change their actin filament partners during contraction. This agrees with a model deduced for other smooth muscles on the basis of physiological experiments and X-ray diffraction analysis.

Venom kinematics during prey capture inConus: the biomechanics of a rapid injection system

“…The thick filament density in SMCb (85±5.6filamentsmm , N5) from the adjacent regions (supplementary materials Fig.S4 and TableS1; P>0.05). Higher thick filament density of SMCs is often correlated with greater peak muscle fiber tension during contraction (Plesch, 1977). SMCb's have smaller, compressed sarcoplasmic reticulum lining their plasma membranes compared with SMCa and longitudinal muscles.…”

Preliminary Observations on the Foot in the Homing Limpets, Siphonaria acmaeoides (Pilsbry) and Patelloida saccharina lanx (Reeve) with Light and Scanning Electron Microscopy

“…All the muscles are smooth irrespective of their orientation and position. The structure of the muscles of the foot in both investigated limpets 1s similar to that of other gastropods (Rogers, 1969;Plesch, 1977;Da Silva and Hodgson, 1987;Trueman and Hodgson, 1990). The distinctive features of the pedal muscles in these animals are a poorly developed sarcoplasmic reticulum and disordered large dense bodies (Trueman and Hodgson, 1990).…”

Ultrastructural investigations on the anterior adductor muscle of a brachiopoda, Lingula unguis.

“…The presence of the core of paramyosin is indicated by striations on the thick myofilaments (1,3,7,9,11,12). These smooth muscle cells can go into a catch state, and the relationship between catch-contraction and paramyosin has been discussed (12).…”

“…The thick myofilaments in the smooth muscles of bivalved adductors characteristically appear to be constructed of a core of paramyosin surrounded by polarized myosin (1,3,8,9,11,12). Paramyosin has been supposed to have some function in catch-contraction (12).…”