The Echinoid Directory

Stenonaster Lambert, 1922, p. 114

[pro Stenonia Desor, 1858, p. 333 (non Gray, 1853); pro Stenocorys Lambert & Thiery, 1917, p. 3 (non Burmeister, 1835)]

Diagnostic Features	Test up to 60 mm in length; thick-plated; flat-based and subconical in profile. Apical disc central; compact and ethmophract with all four genital plates meeting centrally; four gonopores All five ambulacra identical and flush aborally. Plates a little wider than tall. Pore-pairs circumflexed and distinctly larger adapically than ambitally. Towards the ambitus ambulacral plates enlarged and almost as large as interambulacral plates Interambulacral plates with incised sutures and tumid centres aborally Plastron plating undifferentiated. Labral plate a little longer than wide and in contact to the posterior with a single interambulacral plate; subsequent plates biserially arranged and undifferentiated. Peristome small; ovate; relatively close to anterior border but facing down and with no frontal sulcus. Periproct inframarginal but clearly visible in posterior view. No fascioles.
Distribution	Upper Cretaceous (Scaglia, Senonian undifferentiated), Italy, Iran.
Name gender	masculine
Type	Ananchytes tuberculatus Defrance, 1816, p. 41, by original designation.
Species Included	Lambert & Thiery (1921, p. 426) list a second species S. morgani Gauthier from the Senonian of Iran.
Classification and/or Status	Irregularia; Atelostomata incertae sedis Presumed monophyletic
Remarks	A very puzzling taxon on account of its compact ethmophract apical disc but primitive, meridosternous plastron. Closely related to Menuthiaster but differing from that taxon in having a flat base with the periproct much lower, no trace of a peripetalous fasciole and rather domed aboral plates.