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 Monotypic.
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.