The Echinoid Directory

Pliotoxaster Fourtau, 1907, p. 140

Diagnostic Features	Test cordiform with anterior sulcus; posterior face obliquely truncate; lower surface convex. Ambitus rounded. Apical disc ethmophract with four gonopores; genital plate 2 just separating the posterior genital plates but not the posterior oculars; positioned centrally. Anterior ambulacrum sunken from apex to peristome; pore-pairs differentiated with interporal knob; pore-pairs tightly packed aborally and presumably associated with funnel-building tube-feet. Paired ambulacra petaloid; petals bowed, not flexed, with pores of each pair elongate and slit-like; open distally. Peristome small and D-shaped; facing downwards. Labral plate longitudinally elongate, flask-shaped with crescentic horn extending to plate 5.a.2. Sternal plates unequal, with oblique median suture. Episternal plates biserial. Periproct small and rounded; positioned high on posterior truncate face and just visible in aboral view. No fascioles, although granulation is denser and more aligned in the zone between the ends of the petals and the ambitus. Aboral tuberculation of small uniform tubercles set in a groundmass of fine granules.
Distribution	Cretaceous (Aptian to Cenomanian), Europe, Middle East, North Africa, USA.
Name gender	masculine
Type	Pliotoxaster lyonsi Fourtau, 1907, p. 140 [=Toxaster dieneri de Loriol 1887, p. 54] by original designation.
Species Included	P. dieneri de Loriol, 1887; Cenomanian, Egypt and the Middle East. P. comanchei (Clark, 1915); Lower Albian, USA P. inflatus Smiser, 1936; Albian, USA P. whitei Clark, 1893; Albian-Cenomanian, USA. P. renevieri (Wright, 1882); Albian, western Europe. P. collegnoi (Sismonda, 1852); Aptian, France. Probably others, not checked.
Classification and/or Status	Spatangoida, stem group (toxasterids). Paraphyletic (by exclusion of Mecaster).
Remarks	Differs from Toxaster in having the petals sunken and completely free of tubercles perradially. The apical disc also has genital plate 2 separating the two posterior genital plates in the type species at least, in contrast the disc of Toxaster where the two posterior genital plates abut. It differs from Mecaster primarily in having only the beginnings of a diffuse peripetalous fasciole. Fourtau, R. 1907. Bulletin de l'Institut Egyptien, serie 4, 6 (3), p. 140.