Life on the seafloor: adaptations and strategies in Stylophora (Echinodermata)

详细信息    查看全文

• 作者：Fleur Noailles
• 刊名：Lethaia
• 出版年：2016
• 出版时间：July 2016
• 年：2016
• 卷：49
• 期：3
• 页码：365-378
• 全文大小：2036K
• ISSN：1502-3931

文摘

Stylophorans are a Palaeozoic group of non-pentamerous echinoderms, morphologically well-adapted to a benthic mode of life on soft sediment seafloors. By developing a thin and wide theca, they successively increased the surface area in contact with the substrate resulting in an even distribution of the body mass resting on the ground, and efficiently preventing the body from sinking into non-indurated sediments (snowshoe strategy). In stylophorans, the body surface is dramatically increased in result of the expansion of two integumentary areas on the lower thecal surface. While infracentral areas are reduced in primitive forms to the detriment of massive marginals; in boot-shape cornutes, infracentral areas are larger, polyplated and framed by very delicate marginals. In heart-shaped cornutes, the reduction of both infracentral areas is compensated by the development of spiny elements on the theca outline. In forms where the degree of bilateral symmetry is high, the left infracentral area is larger than the right area, resulting in an elongated thecal shape. In structural geology, changes of shape of a rock submitted to a strain can be categorized by translating the obtained deformation into a strain ellipsoid plotted on a Flinn diagram, while in biology changes of shapes of organisms are traditionally measured through morphometric analysis. By applying Flinn's principle of strain ellipsoid to biological objects, the present study aims to characterize different life adaptations across stylophorans, observing changes of shape of both infracentral areas interpreted as two ellipsoids. Once plotted on a Flinn diagram, three significantly separated clusters are observed when focusing on the left area. This concerns forms with reduced infracentral areas, highly and weakly asymmetrical forms. According to these results, three new morphological adaptations are described (water strider, flat fish and stream-lined body). These newly described adaptations enabled snowshoe strategist stylophorans to remain stable on top of the seafloor.