Ruthensteiner Bernhard, Schaefer Kurt
Zoologische Staatsammlung Muenchen, Munich, Germany.
J Morphol. 2002 Jan;251(1):93-102. doi: 10.1002/jmor.1076.
The apical area of larvae of four primitive pulmonate species was investigated by means of serial ultrathin and light microscope sections. Cephalic sensory organs (CSOs) were found in the larvae of Onchidium cf. branchiferum (Onchidiidae) and Laemodonta octanfracta (Ellobiidae), while no trace of the organ was present in the larvae of Ovatella myosotis (Ellobiidae) or Williamia radiata (Siphonariidae). TEM investigation revealed very similar CSOs in O. cf. branchiferum and L. octanfracta, with characteristic putative sensory cell types: ampullary cells with an internal ampulla containing densely packed cilia, para-ampullary cells with external cilia parallel to the surface, and ciliary tuft cells, bearing short ciliary tufts. The epithelium covering the organ has a thick microvillar border with microvilli laterally bearing a pair of electron-dense accumulations and a glycocalyx with interspersed flat plaque-like elements. While homologues of all major elements of the CSO can be found in other gastropod taxa, for example caenogastropods and opisthobranchs, the homology of the ampullary cell with similar cells in nongastropods appears unlikely. The CSO of L. octanfracta is associated with an additional structure, an epithelial external protrusion, lying ventral to the CSO. The absence of the organ in W. radiata weakens hypotheses on the organ's function of examining settlement conditions and velar control.
通过连续超薄切片和光学显微镜切片，对四种原始肺螺类物种幼虫的顶端区域进行了研究。在拟枝背石磺（石磺科）和八裂细纹螺（艾氏螺科）的幼虫中发现了头部感觉器官（CSOs），而在耳状卵螺（艾氏螺科）或辐射威廉螺（笠贝科）的幼虫中未发现该器官的踪迹。透射电镜研究显示，拟枝背石磺和八裂细纹螺的CSOs非常相似，具有特征性的假定感觉细胞类型：具有内部壶腹且壶腹内含有密集排列纤毛的壶腹细胞、具有与表面平行的外部纤毛的壶腹旁细胞以及带有短纤毛束的纤毛簇细胞。覆盖该器官的上皮具有厚的微绒毛边界，微绒毛侧面带有一对电子致密聚集物以及带有散布的扁平斑块状元素的糖萼。虽然在其他腹足类分类群中可以找到CSO所有主要元素的同源物，例如新腹足目和后鳃亚纲，但壶腹细胞与非腹足类中类似细胞的同源性似乎不太可能。八裂细纹螺的CSO与一个额外的结构相关联，即位于CSO腹侧的上皮外部突起。辐射威廉螺中该器官的缺失削弱了关于该器官检查附着条件和缘膜控制功能的假说。
