Is Hrabeiella periglandulata (Annelida, "Polychaeta") the sister group of Clitellata? Evidence from an ultrastructural analysis of the dorsal pharynx in H. periglandulata and Enchytraeus minutus (Annelida, Clitellata)
Is Hrabeiella periglandulata (Annelida, "Polychaeta") the sister group of Clitellata? Evidence from an ultrastructural analysis of the dorsal pharynx in H. periglandulata and Enchytraeus minutus (Annelida, Clitellata)
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Hrabeiella periglandulata（Annelida，“多毛类”）是 Clitellata 的姐妹群吗？
作者：
G. Purschke
陆栖多毛类物种Hrabeiella periglandulata与Clitellata和Parergodrilidae有许多共同的特征，后者代表另一个分类单元的“多毛类”，包括一个陆栖物种。缺乏典型的生殖带，生殖器官的不同结构和位置，精子和毛的不同超微结构以及颈部器官的存在，尽管内部和高度修饰，排除了H。有腺的在有腺的内。因此，收敛进化的clitellate一样的功能，在这些群体中，由于类似的选择压力，一般假设。H. Periglandulata和Clitellata比这两者和Parergodrilidae之间更大，并且不仅包括减少和缺失，而且还包括相对复杂的结构，其中包括背侧定位的咽，迄今为止只知道Clitellata。然而，Hrabeiella和Clitellata之间的同源性和突触形态的可能性从未被认真讨论过，这一观点似乎得到了分子数据的支持。本研究对黑胸蛙（H. periglandulata和在环带物种Enchytraeus minutus。共同的结构包括一个致密的纤毛的背上皮与短和不动的纤毛，一个突出的小根系统，连接到肌肉组织，许多开口的咽腺细胞之间的纤毛细胞，表皮褶皱周围的纤毛，uncilated颊腔，和细胞体的咽腺位于咽上皮外。这使得一般的收敛假设至少是有问题的。这种类型的咽的同源性的可能性进一步得到了大脑感觉器官和中枢神经系统的相应结构的支持。因此，这些特征同样可以更简洁地解释为共形，使H的姐妹群关系。periglandulata和Clitellata可能。
The terrestrial polychaete species Hrabeiella periglandulata has many characters in common with Clitellata and with Parergodrilidae, the latter representing another taxon of "Polychaeta" comprising a terrestrial species. Absence of a typical clitellum, different structure and position of the genital organs, different ultrastructure of the spermatozoa and chaetae as well as the presence of nuchal organs, although internal and highly modified, precluded inclusion of H. periglandulata within Clitellata. Consequently, convergent evolution of the clitellate-like features in these groups due to similar selection pressure was generally assumed. Similarities between H. periglandulata and Clitellata are greater than between both of these and Parergodrilidae and include not only reductions and absences but comparatively complex structures as well, among them the dorsally positioned pharynx, so far only known for Clitellata. However, the possibility of homology and thus synapomorphy between Hrabeiella and Clitellata has never seriously been discussed, a view seemingly supported by molecular data. In the present study an ultrastructural investigation of the dorsal pharynx was undertaken in H. periglandulata and in the clitellate species Enchytraeus minutus. The structures in common include a dense ciliation of the dorsal epithelium with short and immobile cilia, a prominent rootlet system which is connected to the musculature, numerous openings of pharyngeal gland cells between the ciliated cells, a cuticular fold surrounding the cilia, an unciliated buccal cavity, and cell bodies of the pharyngeal glands situated outside the pharyngeal epithelium. This makes the general assumption of convergence at least questionable. Likelihood of homology of this type of pharynx is further supported by the corresponding structure of cerebral sense organs and the central nervous system. Thus, these characters may likewise and more parsimoniously be explained as synapomorphies, making a sister group relationship of H. periglandulata and Clitellata conceivable.