The Echinoid Directory

Crotoclypeus Pomel, 1883, p. 60

[=Dactyloclypeus Maccagno, 1947, p. 126, type species Clypeus wylliei Currie, 1925, p. 63; by subsequent designation of Kier, 1962, p. 37 ]

Diagnostic Features
  • Test large, circular in outline, subconical in profile with greatest height slightly anterior to centre; flat oral surface.
  • Apical system slightly posterior to centre, tetrabasal, madreporite very large, other genital plates small; oculars V and I not in contact with periproct.
  • Petals broad, long, extending to margin; petals II, III and IV longer than V and I. Interporiferous zones slightly wider than poriferous zones, petals open distally. Pores conjugate, outer pore slit-like, inner pore slightly elongated.
  • Periproct supramarginal, midway between apical system and posterior margin (the disc is exocyclic). Opening into a short subanal groove.
  • Peristome slightly anterior, pentagonal; ambulacra only slightly depressed towards peristome.
  • Bourrelets poorly differentiated, confined to inward sloping entrance to peristome, weakly convex.
  • Phyllodes tapering towards peristome, double pored, very long, extending almost to the margin, pore pairs arranged in three series in each half ambulacrum.
  • No buccal pores.
Middle Jurassic (Bajocian), western Europe.
Name gender masculine
Nucleolites agassizii Wright, 1852, p. 308, by subsequent designation of Lambert & Thiery, 1921, p. 344.
Species Included
  • C. agassizii (Wright, 1851); upper Bajocian, England and France.
  • C. trigeri (Cotteau, 1868); Bajocian-Callovian, England and France.
  • C. wylliei (Currie, 1925); Bathonian - Callovian, Somalia.
  • C. subulatus (Young & Bird, 1828); Bajocian-Oxfordian, England, France.
Classification and/or Status
Irregularia; Neognathostomata; \'nucleolitid\'.

Crotoclypeus differs from Clypeus in having its periproct well-separated from the apical disc, with or without catenal plates linking the apical disc and periproct. It is therefore exocyclic, while Clypeus is endocyclic. The test is consistently taller than that of Clypeus.

Crotoclypeus is similar to Dactyloclypeus. Maccagno erected Dactyloclypeus as a new subgenus of Clitopygus (considered by Kier (1962) to be a synonym of Nucleolites). Dactyloclypeus is closer morphologically to Clypeus than Nucleolites. In erecting a subgenus of Clitopygus, Maccagno may have been referring to the work of Lambert & Thiery (1925, p. 586), who synonymised Clitopygus with Crotoclypeus on the basis of the position of the periproct.

According to Kier (1962, p. 35) the presence of catenal plates joining the apical system to the periproct appears to be variable within the genus and even the type species.

Pomel, A. 1883. Classification méthodique et genera des Échinides vivante et fossiles. Thèses présentées a la Faculté des Sciences de Paris pour obtenir le Grade de Docteur ès Sciences Naturelles, 503, 131 pp. Aldolphe Jourdan, Alger.

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

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.