Morita Rihito
Institute of Earth Science, School of Education, Waseda University, Shinjukuku, Tokyo, 161 Japan.
J Morphol. 1991 Jan;207(1):81-92. doi: 10.1002/jmor.1052070110.
Molluscan shells, including those of Gastropoda, are formed by accretionary growth at the mantle edge. The mantle is a thin membrane of skirt-like shape, which extends minutely beyond the aperture, and its edge adds a shell increment to the aperture margin so that each increment copies a configuration of the mantle edge at that time. Thus, regulation of shell morphogeny is almost equivalent to the factors which control the mantle form at the moment of shell growth. Form of the mantle skirt is considered to be kept in a state of balance between the force of its internal stress and forces acting on it such as fluid pressure or muscle contraction. The expansion behavior of the mantle skirt has been numerically analyzed by using an elastic model (DMS-tube), which represents the fundamental structure of the mantle tissue as a double membrane structure with internal springs (DMS). Four characteristic expansion patterns of the DMS-tube have been detected: (1) general outward expansion; (2) developing a ridge-like fold on an initial longitudinal protrusion of the tube edge; (3) drastic shift of the expanded state from a uniformly curved to an elliptical shape in outline, owing to the existence of a fixed boundary condition on the tube wall; and (4) constricted protrusion on the open region of the shell wall surrounding the DMS-tube. These results have the potential for answering the following questions relating to the morphogenesis of gastropod shells. How does the mantle skirt usually make contact with the inner surface of the shell wall so as to ensure continuous accretion of shell materials to the aperture margin? What is the cause of spiral ridges? Why do open coiling or minimally overlapping shells have generally circular apertures, while shells with apertures overlapped by whorls have non-uniformly curved apertural lips? What is the cause of long closed spines and why do they always appear on spiral ridges?
软体动物的壳，包括腹足纲动物的壳，是通过在套膜边缘的增生生长形成的。套膜是一层裙状的薄膜，它微微延伸到壳口之外，其边缘会在壳口边缘增加一层壳质增量，这样每个增量都复制了当时套膜边缘的形态。因此，壳形态发生的调控几乎等同于控制壳生长时套膜形态的因素。套膜裙的形态被认为是在其内部应力与作用于它的力（如流体压力或肌肉收缩力）之间保持平衡的状态。通过使用弹性模型（DMS管）对套膜裙的扩张行为进行了数值分析，该模型将套膜组织的基本结构表示为带有内部弹簧的双层膜结构（DMS）。已检测到DMS管的四种特征性扩张模式：（1）一般向外扩张；（2）在管边缘的初始纵向突出上形成脊状褶皱；（3）由于管壁上存在固定边界条件，扩张状态从均匀弯曲急剧转变为椭圆形轮廓；（4）在围绕DMS管的壳壁开放区域出现收缩突出。这些结果有可能回答以下与腹足纲动物壳形态发生相关的问题。套膜裙通常如何与壳壁的内表面接触，以确保壳材料持续添加到壳口边缘？螺旋脊的成因是什么？为什么开放式盘绕或最小重叠的壳通常有圆形壳口，而壳口被螺层重叠的壳有非均匀弯曲的壳口唇缘？长封闭棘的成因是什么，为什么它们总是出现在螺旋脊上？
