Larval development of Myzostoma cirriferum (Myzostomida)
Larval development of Myzostoma cirriferum (Myzostomida)
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DOI：
10.1002/jmor.10160
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发表时间：
2003-12-01
影响因子：
1.5
通讯作者：
Müller, MCM
中科院分区：
文献类型：
--
作者：
Eeckhaut, I;Fievez, L;Müller, MCM
利用扫描电镜、透射电镜和激光扫描显微镜观察了卷边粘口虫Myzostoma cirriferum的幼虫发育过程。它与其他的Myzostomids相似，包括三个阶段：原担轮、担轮和后担轮。原轮幼虫是一个球形的幼虫，产卵后18-48小时出现在培养物中。它没有内部器官，其身体由三种细胞类型组成：覆盖细胞和纤毛细胞，它们位于外部并被角质层包围，以及填充囊胚腔的静息细胞。担轮幼虫是梨形幼虫，在产卵后20-72小时发育;身体包括与前一阶段相同的三种细胞类型。的metatrochophore是一个梨形的幼虫，发展40小时和14天之间，其特点是存在两束四个chaetae。当完全发育时，后滋养细胞有一个消化系统（由咽，食道和盲消化袋组成），两对原肾管和一个神经系统，包括食道上神经节，食道周围连接，背神经和腹神经。变态一般发生在产卵后7天。在这个时候，后毛柄失去了它的毛，变成腹侧的褶状。超微结构分析表明，毛状体和M. cirriferum metatrochophores与在一些多毛类担轮藻中观察到的结构同源。再加上最近的系统发育分析，Myzostomida被放置在环节动物之外，myzostomid和多毛类幼虫之间的同源性支持的观点，担轮幼虫出现在螺旋进化的早期。J. Morphol. 258：269-283，2003. (C)2003 Wiley-Liss，Inc.
The larval development of Myzostoma cirriferum is described by means of SEM, TEM, and cLSM. It is similar to that of other myzostomids and includes three stages: the protrochophore, the trochophore, and the metatrochophore. The protrochophore is a ball-shaped larva present in culture from 18-48 h after egg laying. It has no internal organs and its body is made of three cell types: covering cells and ciliated cells that are external and surrounded by a cuticle, and resting cells that fill the blastocoel. The trochophore is a pear-shaped larva that develops 20-72 h after egg laying; the body includes the same three cell types as the previous stage. The metatrochophore is a pear-shaped larva that develops between 40 h and 14 days and is characterized by the presence of two bundles of four chaetae. When fully developed, the metatrochophore has a digestive system (made of a pharynx, an esophagus, and a blind digestive pouch), two pairs of protonephridia, and a nervous system composed of a supraesophageal ganglion, circumesophageal connectives, and dorsal and ventral nerves. Metamorphosis generally occurs 7 days after egg laying. At that time, the metatrochophore loses its chaetae and becomes pleated ventrally. This ultrastructural analysis suggests that chaetae and the five ventral longitudinal nerve cords of M. cirriferum metatrochophores are homologous structures to those observed in some polychaete trochophores. Coupled with recent phylogenetic analyses, where the Myzostomida are placed outside the Annelida, homologies between myzostomid and polychaete larvae support the view that a trochophore appeared early during the spiralian evolution. J. Morphol. 258:269-283, 2003. (C) 2003 Wiley-Liss, Inc.