Collin R, Voltzow J
Department of Zoology, University of Washington, Seattle, Washington.
Department of Biology, University of Puerto Rico, Río Piedras Campus, San Juan, Puerto Rico.
J Morphol. 1998 Jan;235(1):77-89. doi: 10.1002/(SICI)1097-4687(199801)235:1<77::AID-JMOR6>3.0.CO;2-L.
The coiled shell of gastropods begins as a cap-shaped lens of organic and calcified material that covers the posterior dorsal side of the larva. During development the cap enlarges to cover the larval visceral mass. Marginal growth then produces the characteristic coiled shell. One model of the initiation of shell coiling in "archaeogastropods" requires that the shell remains flexible and uncalcified until after torsion, and that muscle contraction during torsion deforms the shell. We describe early shell calcification and tested this requirement of the model for the patellogastropod limpets Tectura scutum and Lottia digitalis, the trochids Calliostoma ligatum and Margarites pupillus and the abalone Haliotis kamtschatkana. We determined the stage of initial calcification by staining larvae with the fluorescent calcium marker calcein and observing them with bright field, crossed polarizing filter, and fluorescence microscopy. In T. scutum the earliest observable shell was calcified and calcium was sometimes detected even before the initial shell was visible. Larvae of the other species deposited a noncalcified matrix that was subsequently calcified, and in C. ligatum and M. pupillus this initial calcification was distinctly spotty. Shells of both patellogastropods and the abalone were demonstrably rigid prior to torsion while the shells of the trochids were not. These results suggest that shell coiling in patellogastropods and abalone is not initiated by contraction of the larval retractor muscle during torsion; in trochids this mechanism is possible. However, analysis of camera lucida drawings of pre- and post-torsional shells of T. scutum and C. ligatum did not detect shell shape changes during torsion. J. Morphol. 235:77-89, 1998. © 1998 Wiley-Liss, Inc.
腹足纲动物的螺旋壳最初是一个由有机物质和钙化物质构成的帽状晶状体，覆盖在幼虫的后背侧。在发育过程中，这个帽状物会扩大以覆盖幼虫的内脏团。随后边缘生长形成了特有的螺旋壳。一种关于“古腹足类”动物壳螺旋形成起始的模型认为，壳在扭转之前应保持柔韧且未钙化，并且扭转过程中的肌肉收缩会使壳变形。我们描述了早期壳的钙化情况，并针对笠贝目帽贝科的盾笠贝和指状笠贝、钟螺科的条华钟螺和珍珠钟螺以及红鲍，测试了该模型的这一要求。我们通过用荧光钙标记物钙黄绿素对幼虫进行染色，并利用明场、交叉偏振滤光片和荧光显微镜观察，来确定初始钙化阶段。在盾笠贝中，最早可观察到的壳已经钙化，甚至在初始壳可见之前有时就能检测到钙。其他物种的幼虫先沉积了未钙化的基质，随后才钙化，在条华钟螺和珍珠钟螺中，这种初始钙化明显呈点状。笠贝目帽贝和红鲍的壳在扭转之前显然是坚硬的，而钟螺科的壳则不是。这些结果表明，笠贝目帽贝和红鲍的壳螺旋形成并非由扭转过程中幼虫牵缩肌的收缩引发；在钟螺科中，这种机制是有可能的。然而，对盾笠贝和条华钟螺扭转前后壳的摄像描绘分析并未检测到扭转过程中壳形状的变化。《形态学杂志》235:77 - 89，1998年。©1998威利 - 利斯出版公司。
