Structural and Mechanical Properties of Gastropod Connective and Smooth Muscle Tissue

The pedal integument of terrestrial gastropod Arion rufus is composed mainly of smooth muscle cells (SMCs, 45 %), haemocoelic cavities (36 %), and collagen connective tissue. Using stereological methods, SMC two-dimensional length density (0.12 μm−1), numerical density (426,000 mm−3), and mean distance (31 μm) in the cluster were assessed. The average SMC could be approximated by an ellipsoid 72 μm in length with semi-axes of 3 μm. Three-dimensional reconstructions of SMCs and haemocoelic cavities of gastropod tissue were created using serial thick and semi-thin sections. These reconstructions showed the spatial arrangement of individual SMCs within the tissue: longitudinally, perpendicularly, and obliquely oriented to the main axis of the gastropod body. Using uniaxial mechanical loading with linearly increasing load or elongation at various loading rates (2, 10, and 20 mN/min; 2 and 3 mm/min) in transverse and longitudinal orientations to the main gastropod body axis, the Young’s modulus of elasticity for small (23–27 kPa) and large deformations (49–132 kPa) as well as ultimate stress (105–250 kPa) and strain (300–400 %) were determined. There was a trend toward stiffer integument tissue in the longitudinal direction compared to the transversal direction and toward increasing stiffness with loading velocity.