Microscopic aspects of electrosensory system on the partially euryhaline lesser guitarfish

ABSTRACT The electrosensory system on elasmobranchs consists of subcutaneous electroreceptor organs known as ampullae of Lorenzini. The present study investigated the ampullae of Lorenzini morphology of the lesser guitarfish Zapteryx brevirostris, using light microscopy and scanning electron microscopy. The pore number found in the ventral skin surface is much higher than that found in the dorsal portion, characteristic of species that inhabit the euphotic zone. Under light microscopy it was possible to observe that the wall canal consists of a single layer of squamous epithelial cells. The canal features distal expansion, where the ampullae are located with up to six alveoli. The sensory epithelium of ampullae is composed by cubic cells, with oval nucleus, restricted to the interior of the alveoli. With analysis the clusters under scanning electron microscopy, it was possible to observe the structure and the random arrangement of individual ampullae, canals and nerves. The distribution of dorsal and ventral pores and ampullae in Z. brevirostris resembled those of the same family. The number of alveoli per ampullae was similar to that found in euryhaline elasmobranchs species, suggesting that the morphological organization in Z. brevirostris is linked to its possible evolutionary transitory position among batoids.

摘要 板鳃类（elasmobranchs）的电感觉系统由皮下电感受器器官——洛伦兹壶腹（ampullae of Lorenzini）——构成。本研究采用光学显微镜（light microscopy）与扫描电子显微镜（scanning electron microscopy），对短吻犁头鳐（Zapteryx brevirostris）的洛伦兹壶腹形态开展了观察分析。结果显示，其腹侧皮肤表面的毛孔数量显著高于背侧区域，这是栖息于真光层（euphotic zone）物种的典型特征。光学显微镜观察可见，洛伦兹壶腹的管道管壁由单层鳞状上皮细胞（squamous epithelial cells）构成；该管道具有远端膨大结构，壶腹即位于此处，单个壶腹最多可包含6个小叶。壶腹的感觉上皮由立方上皮细胞（cubic epithelial cells）构成，细胞带有卵圆形细胞核（oval nucleus），且仅分布于小叶内部。通过扫描电子显微镜对集群结构进行分析，可清晰观察到单个壶腹、管道与神经的结构及其随机排布模式。短吻犁头鳐的背侧与腹侧毛孔及壶腹的分布模式，与其所属科的物种特征高度相似。单个壶腹所含小叶的数量，与广盐性板鳃类物种的观测结果相近，这表明短吻犁头鳐的形态组织模式，可能与其在鳐形目鱼类（batoids）中所处的演化过渡位置存在关联。