Myoanatomy of Myzostoma cirriferum (Annelida, Myzostomida): Implications for the evolution of the Myzostomid body plan
Myoanatomy of Myzostoma cirriferum (Annelida, Myzostomida): Implications for the evolution of the Myzostomid body plan
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DOI：
10.1002/jmor.20107
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发表时间：
2013-04-01
影响因子：
1.5
通讯作者：
Bleidorn, Christoph
中科院分区：
文献类型：
--
作者：
Helm, Conrad;Weigert, Anne;Bleidorn, Christoph
罕见的基因组标记系统的研究表明，Myzostomida是环节动物的一个亚群，而基因组分析表明，这个分类群在环节动物中存在早期分歧。然而，成年myzostomids显示出高度专业化的身体计划，缺乏典型的环节动物的功能，如外部体环，体腔与后肾，神经系统的节段神经节。这些功能的推定损失可能是由于寄生/共生的生活方式与棘皮动物myzostomids。相反，幼体的解剖结构和成年运动系统类似环节动物。为了澄清myzostomids的肌解剖是否反映了他们的关系环节动物，我们分析了分布的f-肌动蛋白，肌纤维的一个共同组成部分，Myzostoma cirriferum标本使用鬼笔环肽罗丹明标记结合共聚焦激光扫描显微镜。我们的数据显示，myzostomid体的肌肉组织包括一个外圆层，内纵层，众多的背腹肌，和突出的肌肉的旁足复合体。这些特征与环节动物的肌肉系统的共同结构相一致。与其他环节动物不同的是，M.包括体壁的肌肉组织和足旁屈肌的蔓肌呈现覆盖双侧身体平面的径向对称性。这些发现与裂口类的环节动物亲缘关系相一致，并提示裂口类的部分径向对称性与裂口类的环状对称性有关。cirriferum在本种中次生出现。根据我们的数据，我们提供了一个可能发生在导致这个物种的谱系中的肌纤维重排的场景。J. Morphol.，2013. (c)2012 Wiley Periodicals，Inc.
Studies of rare genomic marker systems suggest that Myzostomida are a subgroup of Annelida and phylogenomic analyses indicate an early divergence of this taxon within annelids. However, adult myzostomids show a highly specialized body plan, which lacks typical annelid features, such as external body annulation, coelomic cavities with metanephridia, and segmental ganglia of the nervous system. The putative loss of these features might be due to the parasitic/symbiotic lifestyle of myzostomids associated with echinoderms. In contrast, the larval anatomy and adult locomotory system resemble those of annelids. To clarify whether the myoanatomy of myzostomids reflects their relationship to annelids, we analyzed the distribution of f-actin, a common component of muscle fibers, in specimens of Myzostoma cirriferum using phalloidin-rhodamine labeling in conjunction with confocal laser-scanning microscopy. Our data reveal that the musculature of the myzostomid body comprises an outer circular layer, an inner longitudinal layer, numerous dorsoventral muscles, and prominent muscles of the parapodial complex. These features correspond well with the common organization of the muscular system in Annelida. In contrast to other annelids, however, several elements of the muscular system in M. cirriferum, including the musculature of the body wall, and the parapodial flexor muscles, exhibit radial symmetry overlaying a bilateral body plan. These findings are in line with the annelid affinity of myzostomids and suggest that the apparent partial radial symmetry of M. cirriferum arose secondarily in this species. Based on our data, we provide a scenario on the rearrangements of muscle fibers that might have taken place in the lineage leading to this species. J. Morphol., 2013. (c) 2012 Wiley Periodicals, Inc.