The Echinoid Directory

• 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, almost no phyllode development adorally.
• Ambulacral plating trigeminate throughout with all elements reaching the perradius; alternating series of small tubercles in each half ambulacrum.
• Interambulacral plates wider than tall; with a single row of up to 8 equal-sized tubercles on each; these rows being separated by narrow bands of miliary granulation. Narrow interradial channel on aboral surface.
• Tubercles imperforate and non-crenulate, those on oral surface a little larger.
• Peristome very large (more than half test diameter), subpentagonal with small buccal notches.
• No sphaeridial pits.
• Presence of basicoronal plate not certain.
• Spines and lantern unknown.

Middle Jurassic (Bajocian) to Lower Cretaceous (Aptian), Europe, North Africa.

Echinus nodulosus Goldfuss, 1826, p. 125,  by original designation

• M. nodulosa (Goldfuss, 1826); Oxfordian-Tithonian, western Europe.
• M. pilos Agassiz, in Agassiz & Desor, 1846; Aptian, France [?=M. pulchella Gras, 1852].
• M. peroni Cotteau, 1883; Bathonian, France.
• M. termieri Lambert, 1931; Bajocian, Morocco.
• M. forbesi (Wright, 1851); Bajocian, England.

Euechinoidea, Echinacea stem group Arbacioida

Presumed monophyletic.

Distinguished from the very similar Polycyphus by having uniserial ambulacra. Distinguished from Codiopsis by its ambulacral plating, which is simple acrosaleniid style. In Codiopsis the perradial suture is clearly zig-zaged defining each triad; in Magnosia the median suture is more or less straight.

M. peroni and M. termieri distinguished by having rather tall plates with up to 5 or 6 rows of small equal tubercles. Distinct genus.

M. caraboeufi Cotteau (1880) [Bajocian, France] is based on small individuals, probably too small to have developed the characteristic differences of ambulacra and are best treated as indet.

Magnosia termieri Lambert, 1931 [Bajocian, Morocco], is a Codiopsis. Its interambulacral plates are tall with a dense array of small tubercles, 5-6 deep, not the single row of subequal primaries.

Michelin, H. 1853. Revue et Magazin de Zoologie 5, p. 34.

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

Smith, A.B. 2011. Gymnodiadema and the Jurassic roots of the Arbacioida (stirodont echinoids). Swiss Journal of Palaeontology 130, 155-171.