Читать книгу Life in the Open Ocean - Joseph J. Torres - Страница 82

Cnidarian tentacles may be considered as a large, loosely configured filter, and the concept of direct interception derives from filtration theory (Rubenstein and Koehl 1977; Purcell 1997). Because the spacing of tentacles in any cnidarian predator is usually much greater than the prey diameter, particularly for small prey, the direct interception of a prey item on a tentacle depends only on the diameter and swimming speed of the prey and the diameter of the tentacle. Further, the theory predicts that larger, faster prey would be selected for by tentaculate predators generally. It applies most directly to ambush predators such as the siphonophores and some of the medusae. Figure 3.16 shows how the ubiquitous medusan predator Pelagia noctiluca captures prey on one of its tentacles while swimming. Prey is trapped by nematocyst discharge and conveyed to the mouth with the cooperation of the oral arms as the Pelagia continues to swim.