The Echinoid Directory

Jesionekechinus Vadet, 1997, p. 128

Diagnostic Features
  • Test pentagonal in outline, weakly conical in profile with concave oral surface.
  • Apical central, large, hemicyclic. posterior genital plates slender; five gonopores. Periproct large.
  • No anal sulcus.
  • Ambulacra non-petaloid; pore-pairs simple isopores. Plating simple above ambitus.
  • Ambulacra on oral surface narrow; plating remains simple but arranged into triads towards the peristome, with pore-pairs uniserial. No buccal pores.
  • Peristome central, circular and sunken with well developed buccal notches.
  • Tuberculation coarser on oral surface and with areoles radially enlarged.
Distribution
Lower Jurassic (Sinemurian), USA.
Name gender masculine
Type
Plesiechinus hawkinsi Jesionek-Szymanska, 1970, p. 416, by original designation. Holotype, University of California Berkeley, Museum of Palaeontology D5510
Species Included
  • Only the type species.
Classification and/or Status

Stem group Irregularia.

Monotypic.

Remarks
Distinguished from Pygaster by its small, compact apical disc.

Jesionek-Szymanska, W. 1970. On a new pygasterid (Echinoidea) from the Jurassic (Middle Lias) of Nevada, U. S. A. Acta Palaeontologica Polonica 15, 411-423, pls 1, 2.

Vadet, A. 1997. Echinides du Callovien de la Sarthe et de l'Orne II - A Les Echinides irreguliers: Analysis et evolution. Memoires de la Societe Academique du Boulonnais Serie Histoire naturelle 18, 73-139.