Article: Holothurians in the Blue Lias of southern Britain
In a detailed study of the Blue Lias (Hettangian-Sinemurian) at four localities in southern Britain holothurian sclerites were found in 76% of samples, sometimes in abundance. There are eleven sclerite morphospecies, four of them new, including examples of the Dactylochirotida (Ypsilothuriidae), Dendro-chirotida (?Cucumariidae), Apodida (Achistridae, Chiridotidae and Synaptidae), Elasipoda and probably Molpadiida (Molpadiidae). Four types of calcareous ring are described and, where possible, their associated sclerite morphospecies identified. A number of microfossils previously assigned to the class are demonstrated to be non-holothurian including Etheridgellidae and Rhabdotites. Calclamna and Binoculites are recognized as growth stages of the same morphotype and their taxonomy revised. The fauna includes the earliest unequivocal records of the order Molpadiida and families Synaptidae and Ypsilothuriidae. New taxa are Acutisclerus plagiacanthus gen. et sp. nov., Palaeoypsilus liassicus gen. et sp. nov, Theelia synapta sp. nov., Priscopedatus sp. nov.?, and the genus Clavallus.The fauna is of limited palaeoenvironmental and biostratigraphical use, although changes in size frequency (Achistrum monochordata) and relative abundance (Binoculites spp.) are potentially informative for the latter. Assemblages are difficult to recognize possibly due to taphonomic effects. The fauna is broadly similar across northwestern Europe but with regional variations both in sclerite composition and abundance.