Early ontogeny and soft tissue preservation in siphonotretide brachiopods: New data from the Cambrian–Ordovician of Iran

New Late Cambrian (Furongian) to Early Ordovician (Tremadocian) assemblages of micromorphic organo-phosphatic (linguliformean) brachiopods from Iran are characterised by the presence of exceptionally well preserved material of the Order Siphonotretida, a small, phylogenetically important group with a very poorly documented Cambrian history. Unlike other known Cambrian siphonotretides, which generally lack true spines, the new Iranian taxa preserve the constant presence of hollow spines from as early as the mid Late Cambrian. Early siphonotretide ontogeny remains poorly known, but new data from the Iranian faunas demonstrate that the dorsal larval shell had two pairs of lobes, indicative probably of the presence of larval setal sacs and possibly a rudiment of the embryonic shell. Morphology of the ventral brephic shell, previously unknown in siphonotretides, confirms earlier observations that the adult siphonotretide pedicle attachment was related entirely to the ventral mantle, and it may not be homologous with the pedicle of other lingulates. Phosphatised setae emerging from hollow spines are described for the first time in siphonotretides, most probably representing a retained primitive character. Siphonobolus priscus and Siphonobolus kalshanehensis are established as new species.