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Abstract：
Asexual reproduction by means of splitting, also called fissiparity, is a common feature in some asterozoan groups, especially in ophiactid brittle stars. Most fissiparous brittle stars show six instead of the usual five rays, live as epibionts on host organisms, and use clonal fragmentation to rapidly colonize secluded habitats and effectively expand the margins of their distribution area. While the biology and ecology of clonal fragmentation are comparatively well understood, virtually nothing is known about the evolution and geological history of that phenomenon. Here, we describe an exceptional fossil of an articulated six-armed brittle star from the Late Jurassic of Germany, showing one body half in the process of regeneration, and assign it to the new species Ophiactis hex sp. nov. Phylogenetic inference shows that the fossil represents the oldest member of the extant family Ophiactidae. Because the Ophiactis hex specimen shows an original six-fold symmetry combined with a morphology typically found in epizoic ophiuroids, in line with recent fissiparous ophiactid relatives, we assume that the regenerating body half is an indication for fissiparity. Ophiactis hex thus shows that fissiparity was established as a means of asexual reproduction in asterozoan echinoderms by the Late Jurassic.
摘要：
通过分裂进行无性繁殖，也称为fissipality，是一些小行星群的共同特征，尤其是在ophiactid脆性恒星中。大多数碎裂的脆性恒星显示出六个射线，而不是通常的五个射线，作为外生体生活在宿主生物上，并利用克隆碎片快速定殖僻静的生境，有效扩大其分布区域的边缘。虽然克隆碎片的生物学和生态学比较好理解，对这种现象的演化和地质历史几乎一无所知。这里,我们描述了一个特殊的化石，来自德国侏罗纪晚期的一个铰接式六臂脆性恒星，显示一半的身体在再生过程中，并将其分配给新物种Ophiactishexsp。11月。系统发育推断表明，该化石代表了现存的蛇形科最古老的成员。因为蛇纹石标本显示出原始的六重对称性，并结合了通常在上蛇类中发现的形态，与最近的粘连性交亲一致，我们假设再生身体的一半是残疾的迹象。因此，蛇形动物表明，侏罗纪晚期在小行星棘皮动物中建立了无性繁殖的一种手段。
