|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||Age range and collections|
Helcionelloida - Helcionellida - Yochelcionellidae
If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
|D.I. MacKinnon 1985||Low, slightly cyrtoconic univalves with a well developed transverse plate, or pegma, that projects ventrally from the anterodorsal shell wall, thus dividing the shell interior into two cavities of markedly unequal size; posterior cavity appreciably larger than the anterior. Shell showing relatively little lateral compression; aperture elongate oval.|