Gladfelter, W.B., 1972. Structure and function of the locomotory system of Polyorchis montereyensis (Cnidaria, Hydrozoa). Helgoländer wiss. Meeresunters. 23 1: 38-79.

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Publication

https://link.springer.com/article/10.1007/BF01616310

figs. 1-24, tabs. 1-4. (xii.1972)

The locomotory system of P. montereyensis Skogsberg was studied in detail. (2) Swimming in P. montereyensis involves the alternating antagonistic action of the subumbrellar swimming muscles and the elastic mesoglea. (3) The swimming muscle consists of striated contractile elements arranged circularly in 4 discontinuous subumbrellar sheels and a sheet on the subumbrellar side of the velum. There is also a sheet of radially arranged fibers on the exumbrellar side of the velum. The 4 subumbrellar sheets are anchored to the bell along the per-and interradii. (4) The mesogleal skeleton consists of 5 components: (a) the matrix of the bell mesoglea, (b) optically visible fibers that traverse the bell from gastrodermal lamella to exumbrella, (c) the basement membrane or supporting lamella, (d) a system of joints, and (e) the velar mesoglea. (5) The morphology, orientation, and distribution of the mesogleal fibers suggest that their major role is maintaining the radial integrity of the bell during deformation. (6) Mesogleal vol remains constant during swimming.Locally the mesoglea is subjected to forces of stretch and compression, but the critical element in narrowing the bell involves bending or folding the mesoglea around a series of structural joints. The fulcrum of these joints is anchored to the exumbrella by concentrations of mesogleal fibers. The joints consist of 8 adradial regions of highly deformable mesoglea lacking visible fibers. The regions are triangular in cross section and are separated from the remainder of the mesoglea (98-99% of the total) by the gastrodermal lamella. A circular apical joint is also present. (7) Sequential changes in shape and position of the bell relative to a fixed grid during contraction and recovery were measured in order to determine such parameters of swimming as rate of contraction, rate of expulsion of water, change in bell velocity during contraction and recovery, momentum, etc. (8) In normal swimming the velum serves mainly to constrict the aperture of the bell, thus increasing the velocity of expelled water, and hence increasing the force driving the medusa forward.Medusae swam with a greatly decreased velocity after velum removal. (9) Turning is accomplished primarily by asymmetrical contraction of the exumbrellar velar radial muscles. The ability to turn was lost after velum removal. (10) Studies of the relationship between individual size and the various parameters of swimming in P. montereyensis show that: (a) the duration of the contraction phase of the swimming beat is roughly proportional to the square root of the subumbrellar circumference (or bell height); (b) smaller individuals swim faster relative to their bell height than do larger ones; (c) the velum is relatively better developed in small animals and plays a proportionately more important role during swimming.

Physiology

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