Purschke Günter, Arendt Detlev, Hausen Harald, Müller Monika C M
Fachbereich Biologie/Chemie, Zoologie, Universität Osnabrüeck, 49069 Osnabrüeck, Germany.
Arthropod Struct Dev. 2006 Dec;35(4):211-30. doi: 10.1016/j.asd.2006.07.005. Epub 2006 Oct 30.
The evolution of photoreceptor cells and eyes in Metazoa is far from being resolved, although recent developmental and morphological studies provided strong evidence for a common origin of photoreceptor cells and existence of sister cell types in early metazoans. Photoreceptor cells are of two types, rhabdomeric and ciliary, depending on which part of the cells is involved in photoreception proper. A crucial point in understanding eye evolution is the explanation of the enormous structural diversity of photoreceptor cells and visual systems, given the general tendency for molecular conservation. One example of such diversity occurs in Annelida. In this taxon three types of photoreceptor cells exist: rhabdomeric, ciliary and phaosomous sensory cells. Whether the latter evolved independently or have been derived from one of the former cell types is still unresolved, since cilia and microvilli are found in these cells. These different photoreceptor cells are present in cerebral ocelli and eyes, in various ectopic ocelli and eyes situated in different places as well as in various photoreceptor-like sense organs. Whereas rhabdomeric cells mostly occur in connection with pigmented supportive cells, the other types are usually found with unpigmented supportive cells. Thus for the latter cells clear evidence for photoreception is still lacking in most cases. However, initial molecular-developmental investigations have shown that in fact ciliary photoreceptor cells exist within Annelida. Certain visual systems are only present during the larval phase and either replaced by the adult eyes or completely reduced during postlarval and adult stages. In the present paper the diversity of cerebral and extracerebral photoreceptor cells and ocelli as well as corresponding organs devoid of shading pigment is reviewed in Annelida.
后生动物中光感受器细胞和眼睛的进化远未得到解决，尽管最近的发育和形态学研究为光感受器细胞的共同起源以及早期后生动物中姐妹细胞类型的存在提供了有力证据。光感受器细胞有两种类型，即微绒毛型和纤毛型，这取决于细胞的哪一部分真正参与光感受。鉴于分子保守的一般趋势，理解眼睛进化的一个关键点是解释光感受器细胞和视觉系统的巨大结构多样性。这种多样性的一个例子发生在环节动物门中。在这个分类群中存在三种类型的光感受器细胞：微绒毛型、纤毛型和色素体感觉细胞。由于在这些细胞中发现了纤毛和微绒毛，后一种类型是独立进化而来还是源自前一种细胞类型之一仍未解决。这些不同的光感受器细胞存在于脑眼和眼睛中，也存在于位于不同位置的各种异位眼以及各种类似光感受器的感觉器官中。微绒毛型细胞大多与有色素的支持细胞相关联，而其他类型通常与无色素的支持细胞一起被发现。因此，在大多数情况下，对于后一种细胞，仍缺乏明确的光感受证据。然而，初步的分子发育研究表明，事实上环节动物门中存在纤毛型光感受器细胞。某些视觉系统仅在幼虫阶段存在，在幼虫后期和成虫阶段要么被成虫眼睛取代，要么完全退化。在本文中，我们综述了环节动物门中脑内和脑外光感受器细胞和眼以及相应无遮光色素器官的多样性。
