L. Agassiz & Desor, 1847, p. 143
single tube foot to all ambulacral plates
phyllodes (adoral zones of food-harvesting tube-feet) developed adorally
no perignathic girdle or lantern.
Lower Jurassic (Toarcian) to Recent.
Neognathostomata have traditionally been divided into a monophyletic Clypeasteroida and a paraphyletic Cassiduloida. Cladistic analysis (Smith 2001) suggests that cassiduloids are a grade taxon comprising a small number of clades leading to the Clypeasteroida. The majority of Jurassic cassiduloids belong to the common stem group of living cassiduloids plus clypeasteroids.
For a key to the modern species of Cassiduloida see Mooi (1990).
The following taxa are Neognathostomata but too poorly known to compare meaningfully: