The Echinoid Directory

Family hyboclypids Barras, 2007

Diagnosis

Stem group atelostomates with:

  • apical system elongate, adjunct and tetrabasal
  • periproct enclosed within apical system (endocyclic condition), opening into longitudinal groove extending to posterior test margin
  • peristome anterior, oval
  • ambulacra subpetaloid, flush with test
  • ambulacral plates double pored throughout
  • bourrelets absent
  • phyllodes short, narrow with two or three series of pore-pairs in each half ambulacrum
Range
Jurassic (Aalenian to Oxfordian) of Europe
Species Included Just two genera are included here. Hyboclypus and Aulacopygus
Classification and/or Status Irregularia, Microstomata, stem group Atelostomata

Informal grouping for a basal paraphyletic grade.
Remarks
 Hyboclypids are a basal paraphyletic grade sister group to all other atelostomates. Like disasteroids they have an elongate apical disc, and this fully encloses the periproct. This informal grade unites forms which primitively retain an anal sulcus. Spatoclypus is very similar in having an aboral periproct opening into a deep anal sulcus, but accessory plates separate the posterior oculars from the posterior genital plates.

Barras, C. G. 2007. Phylogeny of the Jurassic to Early Cretaceous 'Disasteroid' Echinoids (Echinoidea; Echinodermata) and the origins of Spatangoids and Holasteroids. Journal of Systematic Palaeontology 5, 134-161.