The Behavior and the Morphology of Sea Lilies with Shortened Stalks: Implications on the Evolution of Feather Stars
The Behavior and the Morphology of Sea Lilies with Shortened Stalks: Implications on the Evolution of Feather Stars
复制标题
茎短的海百合的行为和形态：对羽毛星演化的影响
作者：
H. Nakano;T. Hibino;Y. Hara;T. Oji;S. Amemiya
摘要现存海百合可分为有柄海百合和无柄羽星两大类。羽星被认为是从有柄的祖先进化而来，失去了大部分的柄，但这两个群体之间存在其他差异。不分节的中背，长而弯曲的冠毛，小花萼，以及游泳的能力，都是海百合没有的羽毛星星特征。为了弄清楚上述哪些特征与羽毛星的柄的丧失直接相关，我们从海百合Metacrinus rotundus上切下柄，并将它们保存在水族馆中。具有缩短的茎的标本能够在没有茎的支撑下用手臂站立和爬行，但没有观察到任何动物游泳。在形态学上，既没有观察到其余节的融合，也没有观察到花萼的尺寸减小，但纤毛在冠部附近变得长且弯曲。因此，现存的海百合具有适应茎损失事件的潜力。观察到标本自动切断大部分的茎，这表明这种潜力实际上是在自然界中使用的。如果羽星的有柄祖先也具有这种潜力，那么这种将柄的减少和纤毛形态的变化联系起来的机制可能在羽星的进化中发挥了重要作用。实验动物学的方法，因为这项研究可能会提供新的见解的进化问题。
Abstract Extant crinoids can be divided into two groups, stalked sea lilies and stalkless feather stars. Feather stars are considered to have evolved from stalked ancestors by losing most of the stalk, but other differences are present between the two groups. The unsegmented centrodorsal, long and curved cirri near the crown, small calyx, and the ability to swim are all feather star features not found in the sea lilies. To figure out which of the above features evolved directly correlating with loss of the stalk in feather stars, we cut off the stalk from the sea lily Metacrinus rotundus and kept them alive in an aquarium. The specimens with shortened stalks were able to stand and crawl with their arms without the support of their stalks, but swimming was not observed for any of the animals. Morphologically, neither fusion of the remaining segments nor the reduction of the size of the calyx were observed, but the cirri became long and curved near the crown. Therefore, the extant sea lilies possess a potential to adapt to incidents of stalk loss. Specimens autotomizing most of their stalks were observed, suggesting that the potential is actually employed in nature. This mechanism linking the reduction of the stalk and the changes in the morphology of cirri may have played an important role in the evolution of the feather stars, if the stalked ancestors of feather stars also possessed this potential. Experimental zoological approaches as this study may provide new insights to the questions of evolution.