The Echinoid Directory

Phymechinus Desor, 1856, p. 133

[=Alternechinus Schluter, 1870, p. 62, type species Alternechinus cretaceus Schluter, 1870; = Jaubertisoma Vadet, Nicolleau & Reboul, 2010 , p. 33, type species Leiosoma jauberti Cotteau, 1863, by original designation.]

Diagnostic Features
  • Test wheel-shaped, flattened below and above.
  • Apical disc small, subcircular; plating generally firmly bound to corona; hemicyclic with genital plate III insert and other ocular plates generally exsert. Periproct relatively large, with smooth outline.
  • Ambulacra polygeminate, with 5-7 elements to a compound plate. Plate compound style unclear, but with most elements reaching the perradius, possibly compound triads. Pore-pairs irregularly biserial aborally and at the ambitus, expanded adorally into well developed phyllodes.
  • Ambulacral plates with single large tubercle; single row of secondaries between the primaries and forming a zig-zag line up perradius.
  • Interambulacral plates wider than tall. A single primary tubercle centrally placed, with much smaller secondary flanking tubercles on adradial and interradial sides on ambital and adoral plates, these never approaching the size of primaries even in the largest individuals. Secondary tuberculation generally rather coarse.
  • Ambulacral and interambulacral tubercles of similar size.
  • No well defined aboral naked interradial zone.
  • Primary tubercles imperforate and non-crenulate; mamelon rather massive.
  • Peristome large, almost flush; buccal notches deep and sharp.
  • Spines and lantern unknown; no primordial interambulacral plate.
Middle Jurassic (Bajocian) to Upper Cretaceous (Maastrichtian), Europe, Middle East.
Name gender masculine
Echinus mirabilis Agassiz, in Agassiz & Desor, 1846, p. 372, by monotypy.
Species Included
  • P. mirabilis (Agassiz, in Agassiz & Desor, 1846); Oxfordian, Europe.
  • P. jauberti (Cotteau, 1863); Bajocian-Bathonian, France - with weak crenulation but identical plate compounding.
  • P. lamberti Savin; Valanginian, France.
  • P. cretaceus (Schluter, 1870); upper Senonian, Germany.
  • P. kunckeli (Cotteau, 1888); Campanian, Algeria
  • P. perplexus Smith, 1995; Maastrichtian, United Arab Emirates.
Classification and/or Status
Euechinoidea, Echinacea, Stomopneustoida, Stomopneustidae
Distinguished from Stomopneustes by having biserial rather than triserial ambulacral zones of pore-pairs.

Desor, E. 1855-1858. Synopsis des echinides fossiles. Reinwald, Paris. lxviii + 490 pp., 44 pls.