The Echinoid Directory

Eucosmus Agassiz, in Agassiz & Desor, 1846, p. 356

[=Eucosmechinus Lambert & Thiery, 1814, p. 270 (objective)]

Diagnostic Features
  • Test subglobular, flattened below, gently domed above.
  • Apical disc small; dicyclic; plates firmly bound to corona. Genital plates wider than tall, with gonopore towards outer point; ocular plates small and pentagonal. A ring of tubercles developed around the inner edge of genital plates encircling the periproct. Periproct relatively large, subcircular.
  • Ambulacra straight; pore-pairs small, uniserial; no oral apical differentiation of pore-pairs, but short phyllodes developed adorally.
  • Ambulacral plating apparently simple, from ambitus adapically, with all elements reaching the perradius; a single series of small tubercles in each half ambulacrum only, with no perradial space. Trigeminate from the ambitus adorally.
  • Interambulacral plates wider than tall; with only one or two rows of up to 8 equal-sized tubercles on each. Narrow interradial channel on aboral surface.
  • T-shaped basicoronal plate present with primary tubercle and projecting interradially.
  • Tubercles imperforate and non-crenulate, without a platform. Tubercles on oral surface a little larger, with relatively large mamelon.
  • Peristome very large (more than half test diameter), subpentagonal with well defined, rimmed buccal notches; no tags.
  • No sphaeridial pits.
  • Spines and lantern unknown.
Distribution Upper Jurassic (Oxfordian-Tithonian) to Lower Cretaceous (Valanginian), Europe, North Africa
Name gender masculine
Type Eucosmus decoratus Agassiz, in Agassiz & Desor, 1847, p. 356, by original designation.
Species Included
  • E. decorata Agassiz, in Agassiz & Desor, 1847; Oxfordian, Europe.
  • E. meslei (Gauthier, 1875); Tithonian, Algeria (differs in having uniserial tubercles at ambitus in ambulacra).
  • E. suessi de Loriol, 1901; Valanginian, Czech Republic.
  • E. ornata Zitt, 1986; Valanginian, Czech Republic.
Classification and/or Status

Euechinoidea, Echinacea, Arbacioida

Presumed monophyletic.


Distinguished from the very similar Magnosia tby having only a double column of tubercles in each ambulacral zone rather than four or more. In E. meslei the ambulacra are so narrow that there are only two columns of ambulacral tubercles which dominate the interporal zone, often alternating. Ambulacral plates are all simple, unlike Codiopsis where two of the three plates in each triad are demiplates. The low, wide plates indicate affinities with the type species of Magnosia rather than with earlier species.

Agassiz, L. & Desor, P. J. E. 1846-1847. Catalogue raisonné des familles, des genres, et des espèces de la classe des échinodermes. Annales des Sciences Naturelles, Troisième Série, Zoologie : 6 (1846): 305-374, pls. 15-16; 7 (1847): 129-168; 8 (1847): 5-35, 355-380.

Mortensen, T. 1935. A monograph of the Echinoidea II. Bothriocidaroida, Melonechinoida, Lepidocentroida and Stirodonta. C. A. Reitzel, Copenhagen