page_title: Helcionelloida
hierarchical_section_title: Helcionelloida
caption_attribution_description: English: Drawing of the apical, apertural and basal view of the fossil of Pelagiella atlantoides - synonym: Cyrtolithes atlantoides.
context_page_description: Helcionelloida is an extinct group of ancient molluscs. These are the oldest known conchiferan molluscs, that is, they had a mineralised shell. Some members of this class were mistaken for Monoplacophorans. The class was erected by Peel in 1991.
context_section_description: Helcionelloida is an extinct group of ancient molluscs (phylum Mollusca).  These are the oldest known conchiferan molluscs, that is, they had a mineralised shell.  Some members of this class were mistaken for Monoplacophorans.  The class was erected by Peel in 1991.
caption: Pelagiella atlantoides
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