Department of Biology, Research Group for Comparative Zoology, University of Copenhagen, Universitetsparken 15, Copenhagen Ø, Denmark.
Evol Dev. 2010 Jan-Feb;12(1):16-24. doi: 10.1111/j.1525-142X.2009.00387.x.
The phylogenetic position of Brachiopoda remains unsettled, and only few recent data on brachiopod organogenesis are currently available. In order to contribute data to questions concerning brachiopod ontogeny and evolution we investigated nervous and muscle system development in the craniiform (inarticulate) brachiopod Novocrania anomala. Larvae of this species are lecithotrophic and have a bilobed body with three pairs of dorsal setal bundles that emerge from the posterior lobe. Fully developed larvae exhibit a network of setae pouch muscles as well as medioventral longitudinal and transversal muscles. After settlement, the anterior and posterior adductor muscles and delicate mantle retractor muscles begin to form. Comparison of the larval muscular system of Novocrania anomala with that of rhynchonelliform (articulate) brachiopod larvae shows that the former has a much simpler muscular organization. The first signal of serotonin-like immunoreactivity appears in fully developed Novocrania anomala larvae, which have an apical organ that consists of four flask-shaped cells and two ventral neurites. These ventral neurites do not stain positively for the axonal marker alpha-tubulin in the larval stages. In the juveniles, the nervous system stained by alpha-tubulin is characterized by two ventral neurite bundles with three commissures. Our data are the first direct proof for the presence of an immunoreactive neurotransmitter in lecithotrophic brachiopod larvae and demonstrate the existence of flask-shaped serotonergic cells in the brachiopod larval apical organ, thus significantly increasing the probability that this cell type was part of the bauplan of the larvae of the last common lophotrochozoan ancestor.
腕足动物的系统发育位置仍未确定，目前仅有少量关于腕足动物器官发生的最新数据。为了为有关腕足动物个体发生和进化的问题提供数据，我们研究了无铰纲腕足动物 Novocrania anomala 的神经和肌肉系统发育。该物种的幼虫是卵黄营养型的，具有双叶体形，有三对背侧刚毛束从后叶伸出。完全发育的幼虫具有刚毛囊肌肉网络以及中背和横向肌肉。在定居后，前、后肌开始形成。将 Novocrania anomala 的幼虫肌肉系统与 Rhynchonelliform（有铰）腕足动物幼虫的肌肉系统进行比较，发现前者的肌肉组织更为简单。完全发育的 Novocrania anomala 幼虫中首次出现类似血清素的免疫反应信号，该幼虫具有由四个烧瓶形细胞和两个腹神经纤维组成的顶端器官。这些腹神经纤维在幼虫阶段不被轴突标记物 alpha-微管蛋白染色。在幼体中，用 alpha-微管蛋白染色的神经系统的特征是有两个带有三个连合的腹神经纤维束。我们的数据是首次直接证明卵黄营养型腕足动物幼虫中存在免疫反应性神经递质的证据，并证明了在腕足动物幼虫的顶端器官中存在烧瓶形 5-羟色胺能细胞，从而大大增加了这种细胞类型是最后共同的担轮动物祖先幼虫体计划的一部分的可能性。
