The bilaterally symmetrical, feeding larval stage is an ancestral condition in echinoderms. However, many echinoderms have evolved abbreviated development and form a pentamerous juvenile without a feeding larva. Abbreviated development with a non-feeding vitellaria larva is found in five families of brittle stars, but very little is known about this type of development. In this study, the external anatomy, ciliary bands, neurons, and muscles were examined in the development of the brooded vitellaria larva of Ophioplocus esmarki. The external morphology throughout development shows typical vitellaria features, including morphogenetic movements to set up the vitellaria body plan, an anterior preoral lobe, a posterior lobe, transverse ciliary bands, and development of juvenile structures on the mid-ventral side. An early population of neurons forms at the base of the preoral lobe at the pre-vitellaria stage after the initial formation of the coelomic cavities. These early neurons may be homologous to the apical neurons that develop in echinoderms with feeding larval forms. Neurons form close to the ciliary bands, but the vitellaria larva lacks the tracts of neurons associated with the ciliary bands found in echinoderms with feeding larvae. Additional neurons form in association with the axial complex and persist into the juvenile stage. Juvenile nerves and muscles form with pentamerous symmetry in the late vitellaria stage in a manner similar to their development within the late ophiopluteus larva. Even though O. esmarki is a brooding brittle star, its developmental sequence retains the general vitellaria shape and structure; however, the vitellaria larvae are unable to swim in the water column.

中文翻译：

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孵化脆星Ophioplocus esmarki 的简略发展

双侧对称的摄食幼虫阶段是棘皮动物的祖先条件。然而，许多棘皮动物已经进化出短小发育并形成了没有摄食幼虫的五体幼体。在五个脆星家族中发现了不进食的黄斑幼虫的简短发育，但对这种发育类型知之甚少。在这项研究中，在 Ophioplocus esmarki 的孵化的 vitellaria 幼虫的发育过程中检查了外部解剖结构、睫状带、神经元和肌肉。整个发育过程中的外部形态显示出典型的黄体特征，包括形成黄体体计划的形态发生运动、前口前叶、后叶、横向睫状带和中腹侧幼体结构的发育。在体腔初始形成后的前黄体阶段，早期的神经元群在口前叶的基部形成。这些早期神经元可能与在棘皮动物中发育的顶端神经元同源，这些神经元以幼虫为食。神经元在睫状带附近形成，但黄斑幼虫缺乏与在棘皮动物中发现的纤毛带相关的神经元束，这些神经元以幼虫为食。额外的神经元与轴复合体相关联并持续到幼年阶段。幼年神经和肌肉在黄斑后期形成五角对称，其方式类似于它们在晚期蛇足幼虫中的发育。尽管 O. esmarki 是一颗沉思的脆星，但它的发育序列保留了一般的黄斑星形和结构；然而，