Department of Earth Sciences and Engineering, South Kensington Campus, Imperial College London, London SW7 2AZ, UK.
Biol Lett. 2011 Feb 23;7(1):146-9. doi: 10.1098/rsbl.2010.0540. Epub 2010 Aug 4.
Soft-bodied taxa comprise an important component of the extant lophophorate fauna, but convincing fossils of soft-bodied lophophorates are extremely rare. A small fossil lophophorate, attached to a brachiopod dorsal valve, is described from the Silurian (Wenlock Series) Herefordshire Lagerstätte of England. This unmineralized organism was bilaterally symmetrical and comprised a subconical body attached basally to the host and partially enclosed by a broad 'hood'; the body bore a small, coiled lophophore. Where the hood attached laterally, there is a series of transverse ridges and furrows. The affinities of this organism probably lie with Brachiopoda; the hood is interpreted as the homologue of a dorsal valve/mantle lobe, and the attachment as the homologue of the ventral valve and/or pedicle. The ridges are arranged in a manner that suggests constructional serial repetition, indicating that they are unlikely to represent mantle canals. Extant brachiopods are not serially structured, but morphological and molecular evidence suggests that their ancestors were. The new organism may belong to the brachiopod stem group, and might also represent a significant element of the Palaeozoic lophophorate fauna.
软躯体类群构成现存担轮动物群的一个重要组成部分,但令人信服的软躯体担轮动物化石极为罕见。本文描述了来自英格兰志留纪(温洛克系列)赫里福德郡原地化石库的一个小型化石担轮动物,附生于腕足动物背壳上。这个未矿化的生物体呈两侧对称,由基部附着在宿主上的圆锥形身体和部分包裹的宽“帽檐”组成;身体上有一个小的、卷曲的担轮。帽檐侧向附着的地方有一系列横向的脊和槽。该生物体的亲缘关系可能与腕足动物有关;帽檐被解释为背壳/套膜叶的同源物,附着处被解释为腹壳和/或肉茎的同源物。这些脊的排列方式表明了构造上的序列重复,表明它们不太可能代表套膜管。现存的腕足动物没有序列结构,但形态学和分子证据表明它们的祖先有。这个新的生物体可能属于腕足动物的原始类群,也可能代表古生代担轮动物群的一个重要组成部分。