A review and classification of fossil didemnid ascidian spicules

Abstract. This study discusses and classifies fossil didemnid ascidian spicules. Three new fossil genera and nine new fossil species are described based on spicule morphology. The genera are Bonetia gen. nov., Rigaudia gen. nov. and Monniotia gen. nov. The species are Bonetia acuta sp. nov., B. brevis sp. nov., B. quasitruncata sp. nov., B. truncata sp. nov., Rigaudia multiradiata sp. nov., R. praecisa sp. nov., Micrascidites pauciradiatus sp. nov., Monniotia acuformis sp. nov., and M. fasciculata sp. nov. Recognizing these distinctive fossil didemnid spicules in fine-grained sediments should provide useful palaeoenvironmental information and may stimulate interest in their biostratigraphy.