| Popis: |
Morphology of the mantle cavity complex and microanatomy of the funnel, collar folds, and retractor muscles were analyzed from 5 specimens of Nautilus pompilius Linnaeus, 1758 to model how these structures perform during respiration and locomotion. In addition to well-known cephalopodium retractors, a pair of short nuchal retractors was found, which attach the collar folds and the wings to the shell. Microstructure of the cephalopodium retractors and the funnel exhibit a typically molluscan pattern of tightly-packed three-dimensional arrangement of muscle fibers. Muscular arrangement in the wings and the nuchal retractors is simpler, consisting of two groups of muscles (longitudinal and transverse) and one group of muscle (longitudinal), correspondingly. Functional conflict was revealed between respiratory and locomotory systems in Nautilus. During jetting, the strong flows produced by the piston-like movements of the head would displace the gills from their working position, pressing them against the ventral wall of the mantle. Flexible support of the gills prohibited intensification of the ventilatory flows and did not allow jet propulsion to become a powerful means of locomotion in Nautilus. Apparently, the evolutionary answer of Nautilus to the dilemma "to breathe or to move," was development of a "quiet respiration pattern" that combined breathing with slow sustained swimming. |
