class of molluscs
They are among the earliest animals with mineralised shells. They are also the oldest known molluscs wth a shell. Some members of this class were mistaken for Monoplacophorans. The class was erected by Peel in 1991.
- Peel J.S. 1991. Functional morphology of the Class Helcionelloida nov., and the early evolution of the Mollusca. In Simonetta A.M. & Conway Morris S. The early evolution of metazoa and the significance of problematic taxa. Cambridge University Press, pp. 157–177. ISBN 978-0-521-40242-2
- P. Yu. Parkhaev (2006) "Adaptive radiation of the Cambrian helcionelloid mollusks (Gastropoda, Archaeobranchia)." In: S.V. Rozhnov (ed.) "Evolution of the biosphere and biodiversity. Towards the 70th anniversary of A. Y. Rozanov". 2006. Moscow, pp. 282-296.
- P. Yu. Parkhaev (2007). "The Cambrian ‘basement’ of gastropod evolution". Geological Society, London, Special Publications 286: 415–421. doi:10.1144/SP286.31. https://books.google.com/books?id=GA7-8JIh9IwC&pg=PA415.