Wiederhold M L, Sharma J S, Driscoll B P, Harrison J L
Department of Otolaryngology, University of Texas Health Science Center, San Antonio 78284-7777.
Hear Res. 1990 Nov;49(1-3):63-78. doi: 10.1016/0378-5955(90)90095-7.
The gravity receptor organs of gastropod molluscs, such as Aplysia californica, are bilateral paired statocysts, which contain dense statoconia within a fluid-filled cyst. Gravitational forces on the statoconia are sensed through their interaction with ciliated mechanoreceptor cells in the wall of the cyst. Larval Aplysia contain a single statolith within each statocyst; when the animals grow to a critical size, they begin producing multiple statoconia, a process that continues throughout life. The number of statoconia is highly correlated with animal weight but poorly correlated with age, indicating that stone production is related to total metabolism. The single statolith has an amorphous internal structure whereas the multiple statoconia have calcification deposited on concentric layers of membrane or matrix protein. The statolith appears to be produced within the cyst lumen but the multiple statoconia are produced within supporting cells between the receptor cells. Large adult animals have statoconia larger than those in early post-metamorphic animals which have just started producing multiple stones. The maximum statocyst diameter at which the receptor-cell cilia can suspend the statolith in the center of the cyst lumen is 45 microns; production of multiple stones begins when the cyst reaches this size. The mechanisms by which statoconia production is initiated and controlled are discussed.
腹足纲软体动物（如加州海兔）的重力感受器器官是双侧成对的平衡囊，在充满液体的囊中含有致密的平衡石。平衡石上的重力通过其与囊壁上的纤毛机械感受器细胞的相互作用来感知。海兔幼虫的每个平衡囊中含有一个单块平衡石；当动物长到临界大小时，它们开始产生多个平衡石，这个过程会持续一生。平衡石的数量与动物体重高度相关，但与年龄相关性较差，这表明平衡石的产生与总代谢有关。单块平衡石具有无定形的内部结构，而多个平衡石则有钙化沉积在膜或基质蛋白的同心层上。平衡石似乎是在囊腔内产生的，而多个平衡石是在感受器细胞之间的支持细胞内产生的。成年大型动物的平衡石比刚开始产生多个平衡石的变态后早期动物的平衡石更大。感受器细胞纤毛能够将平衡石悬浮在囊腔中心的最大平衡囊直径为45微米；当囊达到这个大小时，就开始产生多个平衡石。文中讨论了平衡石产生的起始和控制机制。
