The Echinoid Directory

• Test of small to medium size, subovate, greatest width at centre; low conical in profile.
• Apical system central, tetrabasal, with four gonopores, posterior oculars elongate, catenal plate present (primitive form).
• Petals open, long, extending almost to ambitus, poriferous zones narrowing distally, inner pore round, outer pore greatly elongated transversely; all pores double.
• Periproct aboral, opening into deep anal sulcus that extends to the posterior margin; far removed from the apical disc.
• Peristome anterior, pentagonal, depressed, higher than wide.
• Bourrelets slightly developed.
• Phyllodes slightly widened, double pored, with an inner and an outer series of rounded pore-pairs in each half ambulacrum.
• Buccal pores probably absent.
• No naked zone in posterior interambulacrum orally.

Middle Jurassic (Late Bajocian-Late Bathonian) of France (according to Moyne et al., 2003).

Echinobrissus burgundiae Cotteau, 1871, p. 259; by subsequent designation of Kier, 1962, p. 63.

Pomel (1883) included the following species when erecting this genus: Echinobrissus burgundiae, Perronii, Brodiei, slaviensis, Renevieri, rotundus, gibbosus.

Irregularia; Neognathostomata; 'nucleolitid'.

Subjective junior synonym of Nucleolites Lamarck, 1801.

Pomel (1883) distinguished this from Clitopygus with a similar peristome and periproct, because its madreporite was supposedly button-like and dominant, with other apical disc plates much smaller and arranged as a circle around, and by its more elongate outer pores in the petals.

Acromazus is distinguished from the type species of Nucleolites by the presence of a catenal plate between the posterior genital plates. This primitive condition (additional plates and advanced apex-periproct link) separates N. burgundiae and N. hugii (Agassiz, 1839) from other Jurassic Nucleolites (see Moyne et al., 2003, 2005). Due to the range from primitive to advanced conditions seen among the Nucleolites, such characters are not sufficient to maintain Acromazus as a separate genus.

According to Barras (2006), however, the lectotypes of hugi (Barras, 2006: text-fig. 43a) and burgundiae (Barras, 2006: text-fig. 43c) have completely different apical discs than illustrated by Moyne et al. (2003, 2005), having an enlarged madreporite separating all other genital plates from each other - a condition also seen in the lectotype of N. scutatus Lamarck, 1816, the type-species of the genus (Barras, 2006: text-fig. 43d). This is further evidence for the synonymy of Acromazus with Nucleolites, but raises the question as to the correct specific identity of Nucleolites species with a single catenal plate in the apical disc.

Barras, C. G. 2006. British Jurassic irregular echinoids.  Monographs of the Palaeontographical Society, number 625: 1-168.

S. Moyne, J. Thierry & D. Marchand. (2003). Analysis of the disparity of Nucleolites (Echinoidea, Cassiduloidea) from the Middle-Late Jurassic of the Paris Basin: Taxonomic and biodiversity implications. Proceedings of the sixth European conference on Echinoderm research, Echinoderm Research 2001, J. Feral, B. David (eds). A. A. Balkema, Netherlands. 105-112 pp.

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

A. Pomel. 1883. Classification methodique et genera des echinides vivants et fossiles. A. Jourdan, Paris.