The Echinoid Directory

Hyboclypus L. Agassiz, 1839, p. 74

[=Hyboclypeus Cotteau & Triger, 1869, p. 416 (nomen null.) ]

Diagnostic Features
  • Test medium to large size, ovate in outline, depressed to subconical in profile with slightly tumid oral surface a little sunken towards peristome.
  • Apical system tetrabasal, elongate, adjunct, oculars II and IV in contact; a small number of catenal plates incorporated into the posterior portion of the disc.
  • Ambulacra weakly subpetaloid aborally, all ambulacra similar; narrow and straight.
  • Pores double throughout.
  • Periproct surrounded by plates of the apical system (endocyclic), opening into longitudinal groove that extends to the posterior margin.
  • Peristome anterior, depressed, subcircular with short vertical walled entrance.
  • No bourrelets.
  • Phyllodes short, not expanded; pore-pairs in arcs of three forming broad bands adorally.
  • No buccal pores.
  • Tubercles slightly larger adorally than adapically.
Distribution
Jurassic (Bajocian to Oxfordian), Europe.
Name gender masculine
Type
Hyboclypus gibberulus L. Agassiz, 1839, p. 75, by monotypy.
Species Included
  • H. gibberulus L. Agassiz, 1839; Bajocian to Oxfordian, western Europe.
  • H. sandalinus Merion, in Desor, 1857; Callovian to Oxfordian, western Europe.
Classification and/or Status

Irregularia; stem group Atelostomata.

Basal grade

Remarks

Hyboclypus has often been placed in the Galeropygidae Lambert, 1911, together with Aulacopygus and Galeropygus. The compact apical disc of Galeropygus, coupled with long phyllodes that stretch over much of the oral surface, suggest its affinities lie with the cassiduloids. The elongate apical disc of Hyboclypus and Aulacopygus places these taxa as basal within the Atelostomata.

Hyboclypus and Aulacopygus are distinguished on differences in the structure of their apical systems. In both, the apical disc is elongate, with complemental plates separating genital plates 1 and 4. However, in Aulacopygus the complemental plates also completely separate oculars II and IV, whereas in Hyboclypus such complemental pales only partially separate oculars II and IV. It is worth noting, however, that Kier (1962, p. 29) did not believe this difference to be of generic significance, and considered Hyboclypus the senior subjective synonym of Aulacopygus. Spatoclypus also has an elongate apical disc and an anal sulcus, but differs in having the posterior ocular plates separated from the remainder of the apical disc.

Agassiz, L. 1839. Description des Échinodermes fossiles de la Suisse. Première partie, Spatangoides et Clypéasteroides. Mémoires de la Société helvétique des Sciences naturelles, 3, i-viii + 1-101, 14 pls.

Barras, C. 2006. British Jurassic irregular echinoids. Monograph of the Palaeontographical Society, 1-168, pls 1-14 (publication number 625).

Kier, P. M. 1962. Revision of the cassiduloid echinoids. Smithsonian Miscellaneous Collections 144 (3), 262 pp.

Jesionek-Szymanska, W. 1963. Echinides irreguliers du dogger de pologne. Acta Palaeontologica Polonica 8, 293-397, pls 1-7.