The Echinoid Directory

Contributed by Andrew Smith, August 2008

Pronucleolites Barras, 2006, p. 60

Diagnostic Features
  • Test relatively small and rounded to weakly subquadrate in outline 
  • Apical disc tetrabasal; central with 4 gonopores. Posterior genital plates and posterior ocular plates separated by a series of small catenal plates which form a continuous band from the anterior genital plates to the opening of the periproct.
  • Ambulacra petaloid on aboral surface with outer pore in each pair elongate
  • Phyllodes developed adorally with every third pore-pair insert forming an inner and outer column in each half ambulacrum.
  • Basicoronal plate present in interambulacra, small and forming an inturned well to the peristome.
  • Peristome weakly pentalobate, subcentral
  • Periproct on aboral surface half-way between apiex and posterior border.  A line of catenal plates separates the two columns of interambulacral plates above the periproct.  A distinct anal sulcus leads from the periproct towards the posterior ambitus
Distribution Jurassic (Bathonian-Oxfordian), Europe
Name gender masculine
Type Clypeus orbicularis Phillips, 1829, p. 144, 189, pl. 7, fig. 3.

Lectotype of Clypeus orbicularis Phillips, 1829: Oxford University Museum J7366
Species Included Only the type species included for certain. 
Classification and/or Status Irregularia; Cassiduloida; stem group

Remarks Distinguished from Nucleolites and its relatives by having a primitive apical disc structure with catenal plates separating left and right genital and ocular plates behind genital plates 2 and 3.  In this respect the disc is very like that of Galeropygus and Clypeus. However Pronucleolites differs from those two taxa in having nucleolitid-style phyllodes, in which every third pore is insert to form a second discrete column of pore-pairs.

Barras, C. G. 2006. British Jurassic irregular echinoids. Monograph of the Palaeontographical Society no. 625 (part of volume 159 for 2005), 1-168, pls 1-14.