CRYPTOSCHISMA (BLASTOIDEA): A CAMBRIAN-STYLE SEDIMENT STICKER ECHINODERM FROM THE LOWER DEVONIAN OF SPAIN

Cambrian substrates document the transition from Proterozoic-style soft sediment environments with well developed microbial mats and a sharply defined sediment-water inferface to Phanerozoic-style soft substrates with a well-developed mixed layer and a diffuse sediment-water interface. The new Phanerozoic style seafloors resulted in relatively greater water content of the sediment and a blurry water sediment interface, which led to the first appearance of a mixed layer. The effect of this change in dominant substrate types on the ecology and evolution of benthic metazoans has been termed the Cambrian substrate revolution, and was a global event of primary importance for the early diversification of echinoderms. Previously Cambrian-style blastozoans with a sediment sticker attachment strategy have only been reported from Early and Middle Cambrian ecosystems . Cryptoschisma is a sediment sticker blastoid that occupied an anachronistic environment preserved in the La Vid Formation (Lower Devonian) of Spain. Cryptoschisma lived in deep water (below storm wave base) associated with microbially mediated mud mounds. Blastoid communities containing Cryptoschisma show high levels of abundance reaching 990 individuals per square meter in one sample. The typical blastoid stem is flexible being composed of thin columnals but in Cryptoschisma it is composed of elongate columnals and is unique among blastoids in forming a rigid stick that tapers to a point at the terminus. The lack of roots or cirri and the presence of tapered terminus suggest it used its stem to elevate approximately one to two centimeters above a firm substrate. Although other blastoid genera are found in moderate abundance in more typical environments within the La Vid Formation, Cryptoschisma is not. This find suggest the survival of Cambrian ecologic strategies among blastozoans in very specific environments later in the Palaeozoic.