Drushel R F, Neustadter D M, Shallenberger L L, Crago P E, Chiel H J
Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA.
J Exp Biol. 1997 Feb;200(Pt 4):735-52. doi: 10.1242/jeb.200.4.735.
Changes in the positions, shapes and movements of the feeding apparatus (buccal mass) of the marine mollusc Aplysia californica were studied in intact, transilluminated juveniles. The buccal mass assumes characteristic shapes as its internal structure, the radula/odontophore, moves anteriorly (protracts) or posteriorly (retracts). These shapes are especially distinctive when the radula/odontophore has protracted forwards fully, is close to its resting or neutral position, or has retracted backwards fully. We refer to the shapes that occur at full protraction, transition and full retraction as shape 1 (spherical), shape 2 (ovoid) and shape 3 (gamma-shaped), respectively. We introduce this shape nomenclature in order to avoid confusion with the existing terms protraction and retraction, which we reserve exclusively to describe the direction of movement of the radula/odontophore. The observed shape changes do not agree with those predicted on the basis of in vitro observations of a feeding head preparation, but are similar to shapes observed in vitro in the snail Lymnaea stagnalis. The buccal mass also rotates approximately 10 degrees dorsally during retraction, pivoting on the attachment to the mouth, before the subsequent protraction and return of the buccal mass to the transition shape. This rotation may be due to activation of the extrinsic muscles of the buccal mass. Plots of the buccal mass shape parameters eccentricity versus ellipticity create a two-dimensional shape space, which accurately quantifies the subtle transitions of shape between the different phases of the feeding cycle. Quantitative differences are observed between pure swallows and swallows with tearing behavior, but the qualitative shapes are similar. Hysteresis in the shape space plots of most swallows provides evidence for the hypothesis that protraction and retraction each have distinct 'active' and 'return' phases. The observed kinematic pattern imposes constraints on the internal structures of the buccal mass and may be used to infer the shape and positions of the radula and odontophore.
在完整的、经透照的幼年加利福尼亚海兔（Aplysia californica）中，研究了其摄食器官（口球）的位置、形状和运动变化。随着其内部结构齿舌/齿舌载体向前（伸展）或向后（收缩）移动，口球呈现出特定的形状。当齿舌/齿舌载体完全向前伸展、接近其静止或中性位置或完全向后收缩时，这些形状尤为独特。我们将在完全伸展、过渡和完全收缩时出现的形状分别称为形状1（球形）、形状2（卵形）和形状3（伽马形）。我们引入这种形状命名法是为了避免与现有的术语伸展和收缩混淆，我们仅保留这两个术语来描述齿舌/齿舌载体的运动方向。观察到的形状变化与基于摄食头部制剂的体外观察所预测的变化不一致，但与在体外观察到的静水椎实螺（Lymnaea stagnalis）的形状相似。在收缩过程中，口球还会在与口部的连接处旋转约10度背向转动，然后口球随后伸展并恢复到过渡形状。这种旋转可能是由于口球外部肌肉的激活。口球形状参数偏心率与椭圆率的绘图创建了一个二维形状空间，该空间准确地量化了摄食周期不同阶段之间形状的细微转变。在纯粹吞咽和伴有撕裂行为的吞咽之间观察到了定量差异，但定性形状相似。大多数吞咽的形状空间图中的滞后现象为以下假设提供了证据：伸展和收缩各自具有不同的“主动”和“返回”阶段。观察到的运动模式对口球的内部结构施加了限制，并可用于推断齿舌和齿舌载体的形状和位置。
