. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LOCOMOTION OF EUAPTA 97 (a). FIGURE 1. Diagrams showing the external shape of the apodous holothurian Euapta lappa. (a) Seven warts are shown with the muscles that delineate them: solid lines indicate muscles in state of tonus; broken lines indicate relaxed circular muscles; (b) body of Euapta with a direct overlapping peristaltic wave passing from right to left; B, initial contraction of longitudinal muscle; C, contraction of circular muscle and further longitudinal muscle con- tractions; D, relaxation of all muscles: body

- Image ID: RHN857
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LOCOMOTION OF EUAPTA 97 (a). FIGURE 1. Diagrams showing the external shape of the apodous holothurian Euapta lappa. (a) Seven warts are shown with the muscles that delineate them: solid lines indicate muscles in state of tonus; broken lines indicate relaxed circular muscles; (b) body of Euapta with a direct overlapping peristaltic wave passing from right to left; B, initial contraction of longitudinal muscle; C, contraction of circular muscle and further longitudinal muscle con- tractions; D, relaxation of all muscles: body
Library Book Collection / Alamy Stock Photo
Image ID: RHN857
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LOCOMOTION OF EUAPTA 97 (a). FIGURE 1. Diagrams showing the external shape of the apodous holothurian Euapta lappa. (a) Seven warts are shown with the muscles that delineate them: solid lines indicate muscles in state of tonus; broken lines indicate relaxed circular muscles; (b) body of Euapta with a direct overlapping peristaltic wave passing from right to left; B, initial contraction of longitudinal muscle; C, contraction of circular muscle and further longitudinal muscle con- tractions; D, relaxation of all muscles: body wall distended by coelomic pressure; E, state of tonus. traction of circular muscles releases the body wall from its attachment to the substratum, thus facilitating forward movement. The direct overlapping peristalsis described above is the most common method of locomotion in Euapta, but variations do exist as a result of the reduction or complete suppression of some of its components. One type of wave, direct longi- tudinal peristalsis, is characterized by longitudinal muscular contractions as ob- served in the direct overlapping peristalsis, but there is no accompanying wave of circular contraction. Direct longitudinal peristalsis is observed when the animal crawls across smooth glass surfaces and when it is climbing up a vertical aquarium wall clinging by its tentacles with part or all of its body hanging free below. Sometimes this direct longitudinal paristalsis passes along a body cylinder which is in a tonus state of circular contraction. At other times the body cylinder is constricted throughout part or all of its length by continuous contraction of cir- cular muscles. This obliterates all warts and holds the body diameter constant while waves of only longitudinal contraction pass along the body. In these two cases of waves of longitudinal muscle contraction passing along a body cylinder of unchanging diameter, it is clear that friction is minimal and offers little help

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