The Echinoid Directory

Family Pericosmidae Lambert, 1905, p. 153


 Paleopneustinid spatangoids with:

  • thick-shelled test with frontal groove;
  • apical disc with three gonopores (no gonopore in genital plate 2);
  • ambulacrum III pores differentiated, associated with suckered tube-feet;
  • paired ambulacra petaloid; petals short, narrow, parallel-sided and with occluded plates at end;
  • peristome with projecting labral plate and well developed but short phyllodes;
  • labral plate stout and longitudinally elongate; extending to second ambulacral plate. Sternal plates long and symmetrical. Episternal plates biserially offset; not indented to rear by ambulacral plates;
  • periproct large and marginal; bounded by interambulacral plates 5a/b on oral side;
  • marginal and peripetalous fascioles present.
Palaeocene to Recent; widespread.
Distinguished from the Paleopneustidae by the rather short, sunken petals, well developed frontal groove and suckered tube-feet. Stem group Protenastridae have no occluded plates at the ends of their petals and their marginal and peripetalous fascioles are often coalesced in the anterior interambulacra.