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海蜘蛛寡聚幼虫再探讨。

Oligomeric larvae of the pycnogonids revisited.

作者信息

Alexeeva Nina, Bogomolova Ekaterina, Tamberg Yuta, Shunatova Natalia

机构信息

Department of Invertebrate Zoology, St. Petersburg State University, Universitetskaja nab. 7/9, St. Petersburg, 199034, Russian Federation.

Department of Invertebrate Zoology, Moscow State University, Leninskie gory, 1, 12, Moscow, 119234, Russian Federation.

出版信息

J Morphol. 2017 Sep;278(9):1284-1304. doi: 10.1002/jmor.20713. Epub 2017 Jun 2.

Abstract

Organization and ultrastructure of the protonymphon larva were never adequately described, despite it being the common larval type of the enigmatic sea spiders and the only example of oligosegmented life stage among recent chelicerates. We have made a comprehensive examination of the newly hatched free-living protonymphons of Nymphon brevirostre using SEM, TEM, light, and confocal microscopy. Although fairly typical in their broad characters, protonymphon larvae have a number of unique and unexpected traits. Body cavity, already present at this stage, is lined with extracellular matrix and thus is conclusively identified as primary body cavity. Central nervous system includes four postocular neuromeres arranged in three ganglia: supraesophageal, subesophageal, and the first ganglion of the ventral nerve cord. Examination of the sensory organs revealed unusually organized eyes, mechanoreceptors, and chemoreceptors. We have uncovered a mixed sensory-secretory nature of chelar glands and proposed possible modalities of its receptory part. We gave first descriptions of the complex ultrastructure of three secretory organs (spinning glands, slit-like organs, proboscis glands) and hypothesized on their mode of functioning. Comparisons with another oligomeric larva, for example, nauplius, revealed discrepancies in the segmentation of these animals. Although both larvae are externally unsegmented and bear three pairs of homologous appendages, the protonymphon body includes a fourth segment of the prospective walking legs which is absent in nauplius.

摘要

尽管质子幼体是神秘海蜘蛛常见的幼体类型,也是现存螯肢动物中寡节生活阶段的唯一例子,但此前从未对其组织和超微结构进行过充分描述。我们使用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、光学显微镜和共聚焦显微镜,对新孵化的短吻海蛛自由生活的质子幼体进行了全面检查。虽然质子幼体在广泛特征上相当典型,但它们具有许多独特且出乎意料的特征。在此阶段已经存在的体腔内衬有细胞外基质,因此最终被确定为原体腔。中枢神经系统包括四个眼后神经节,排列在三个神经节中:食管上神经节、食管下神经节和腹神经索的第一神经节。对感觉器官的检查揭示了眼睛、机械感受器和化学感受器的异常组织方式。我们发现了螯腺的混合感觉 - 分泌性质,并提出了其感受部分可能的模式。我们首次描述了三种分泌器官(纺丝腺、狭缝状器官、吻腺)的复杂超微结构,并对其功能模式进行了假设。与另一种寡节幼体(例如无节幼体)的比较揭示了这些动物在分节上的差异。尽管两种幼体在外部都不分节且都有三对同源附肢,但质子幼体的身体包括未来步行腿的第四个体节,而无节幼体中不存在这一体节。

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