Stricker S A, Reed C G
J Morphol. 1985 Mar;183(3):233-50. doi: 10.1002/jmor.1051830302.
The morphology of the mantle in free-swimming and metamorphosing larvae of the articulate brachiopod Terebratalia transversa has been examined by scanning and transmission electron microscopy. The mantle begins to form approximately 2 days after fertilization and subsequently develops into a skirtlike lobe that encircles the middle region of the larval body. A simple epithelium covers both the outer surface of the mantle lobe and the inner side situated next to the pedicle lobe of the larva. During metamorphosis, the mantle lobe is everted over the anterior end of the larva. Thus, the epithelium covering the outer part of the mantle lobe in the larva subsequently becomes the inner epithelium of the juvenile mantle. Similarly, the inner epithelium of the larval mantle lobe represents the future outer epithelium of the juvenile mantle. In free-swimming larvae, the prospective outer mantle epithelium contains two types of cells, called "lobate" and "vesicular" cells. Lobate cells initially deposit a thin layer of amorphous material, and vesicular cells produce ovoid multigranular bodies. Following settlement at about 5 days postfertilization, the vesicular cells secrete an electron-dense sheet that constitutes the basal layer of the developing periostracum. Within several hours to a day thereafter, reversal of the mantle lobe is rapidly effected, apparently by contractions of the pedicle adjustor muscles.
通过扫描电子显微镜和透射电子显微镜，对有铰腕足动物横裂贝自由游动和变态幼虫的外套膜形态进行了研究。外套膜在受精后约2天开始形成，随后发育成围绕幼虫身体中部区域的裙状叶。单层上皮覆盖着外套膜叶的外表面以及幼虫靠近肉茎叶一侧的内侧。在变态过程中，外套膜叶外翻至幼虫前端。因此，幼虫中外套膜叶外部的上皮随后成为幼体外套膜的内部上皮。同样，幼虫外套膜叶的内部上皮代表幼体外套膜未来的外部上皮。在自由游动的幼虫中，未来的外套膜外部上皮包含两种类型的细胞，称为“叶状”细胞和“泡状”细胞。叶状细胞最初沉积一层薄的无定形物质，泡状细胞产生卵形多颗粒体。在受精后约5天沉降后，泡状细胞分泌一层电子致密片，构成发育中的壳皮层的基底层。此后数小时至一天内，外套膜叶迅速反转，显然是通过肉茎调节肌的收缩实现的。
