Murray, 1876
Diagnosis
Phaeodaria with a monaxial heteropolar, ovate to lenticular shell, with reticulate surface sculpture of regular hexagonal indentations resembling the areolate structure of diatoms, with a mouth usually with teeth.
Various authors have revised individual challengerid genera and/or transferred species from their original genera. However, these piecemeal efforts have sometimes resulted in conflicting generic criteria, and a comprehensive natural classification of the entire family is still needed. We attempt in the generic diagnoses below to use non-overlapping criteria that are consistent with both the original definitions and the observed characters of the species discussed. It is provisional for the purposes of this review, and should not be interpreted as proposing emendation of any of the genera treated.
1a Shell without large fenestrae near peristome —> 2
1b Shell with two large fenestrae near peristome, two oral teeth on peristome, and
one or more marginal spines: Genus Challengeranium
2a Margin of shell smooth or with one or two isolated teeth —>3
2b Margin of shell with row of numerous marginal spines, with oral teeth: Genus Challengeron
3a With one oral tooth, no marginal spines: Genus Challengeria
3b With two or more oral teeth, margin smooth or with one or two isolated teeth: Genus Protocystis