Neves Ricardo C, Cunha Marina R, Funch Peter, Kristensen Reinhardt M, Wanninger Andreas
Centro de Estudos do Ambiente e do Mar, Departamento de Biologia, Universidade de Aveiro, Campus Universitário de Santiago, 3810 - 193 Aveiro, Portugal.
J Morphol. 2010 May;271(5):596-611. doi: 10.1002/jmor.10819.
The metazoan phylum Cycliophora includes small cryptic epibionts that live attached to the mouthparts of clawed lobsters. The life cycle is complex, with alternating sexual and asexual generations, and involves several sessile and free-living stages. So far, the morphological and genetic characterization of cycliophorans has been unable to clarify the phylogenetic position of the phylum. In this study, we add new details on the muscular anatomy of the feeding stage, the attached Prometheus larva, the dwarf male, and the female of one of the two hitherto described species, Symbion pandora. The musculature of the feeding stage is composed of myofibers that run longitudinally in the buccal funnel (two fibers) and in the trunk (variable number of fibers). The mouth opening is lined by a myoepithelial ring musculature. A complex myoepithelial sphincter is situated proximal to the anus. In the attached Prometheus larva, three longitudinal sets of myofilaments run dorsally, laterally, and ventrally along the entire anterior-posterior body axis. The muscular architecture of the dwarf male is complex, especially close to the penis, in the posterior part of the body. An X-shaped muscle structure is found on the dorsal side, whereas on the ventral side, longitudinal muscles and a V-shaped muscle structure are present. These muscles are complemented by additional dorsoventral muscles. The mesodermal muscle fibers attach to the cuticle via the epidermis in all life cycle stages studied herein. The musculature of the female is similar to that of the Pandora larva of Symbion americanus and includes dorsoventral muscles and longitudinal muscles that run in the dorsal and ventral body region. Overall, our results reveal striking similarities in the muscular arrangement of the life cycle stages of both Symbion species.
后生动物门环口动物纲包括附着在螯龙虾口器上生活的小型隐匿体表共生生物。其生命周期复杂，有有性和无性世代交替，涉及多个固着和自由生活阶段。到目前为止，环口动物的形态学和遗传学特征仍无法明确该纲的系统发育位置。在本研究中，我们补充了关于迄今已描述的两个物种之一潘多拉共生菌（Symbion pandora）的摄食阶段、附着的普罗米修斯幼虫、矮雄和雌体肌肉解剖结构的新细节。摄食阶段的肌肉组织由在口漏斗（两根纤维）和躯干（纤维数量可变）中纵向排列的肌纤维组成。口部开口由肌上皮环形肌肉组织环绕。一个复杂的肌上皮括约肌位于肛门近端。在附着的普罗米修斯幼虫中，三组纵向肌丝沿整个前后体轴在背侧、外侧和腹侧延伸。矮雄的肌肉结构复杂，特别是在身体后部靠近阴茎的部位。在背侧发现一个X形肌肉结构，而在腹侧有纵向肌肉和一个V形肌肉结构。这些肌肉由额外的背腹肌肉补充。在本文研究的所有生命周期阶段，中胚层肌纤维通过表皮附着于角质层。雌体的肌肉组织与美洲共生菌（Symbion americanus）的潘多拉幼虫相似，包括在背侧和腹侧身体区域延伸的背腹肌肉和纵向肌肉。总体而言，我们的结果揭示了两种共生菌生命周期阶段肌肉排列的显著相似性。
