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The Echinoid Directory

Plesiozonus De Meijere, 1902, p. 12

Diagnostic Features
  • Test ovate with faint anterior sulcus or none; test domed in profile with flat base.
  • Apical disc ethmolytic with three gonopores; central.
  • Anterior ambulacrum narrow; flush to weakly depressed aborally and faintly depressed from ambitus adorally; pore-pairs small and simple.
  • Petals long, flush, parallel-sided and extending to ambitus; open distally, with occluded plates at the ends. Perradial zone not much larger than width of one pore-pair.
  • Peristome kidney-shaped and facing forward into shallow frontal groove. Labrum projecting to cover most of peristome in oral view.
  • Plastron plating: labral plate subquadrate, extending to ambulacral plate 2. Sternal plates elongate, extending to ambulacral plate 5. Episternal plates more or less symmetrical and opposite; large. Post-episternal plates also symmetrical and paired.
  • Lateral interambulacra on oral surface: Interambulacrum 1 is meridoplacous, interambulacrum 5 amphiplacous.
  • Periproct inframarginal; bounded orally by interambulacral plates 4a/b.
  • Peripetalous fasciole present only around the base of anterior paired petals.
  • Marginal fasciole present, crossing interambulacral plate 4 beneath the periproct.
Distribution
Recent, Philippines.
Name gender masculine
Type
Plesiozonus hirsutus De Meijere, 1902, p. 12, by original designation.
Species Included
  • P. diomedeae Mortensen, 1948; Recent, Philippines.
  • P. hirsutus De Meijere, 1902; Recent, Philippines.
  • P. tenuis David & De Ridder, 1989; Recent, Philippines.
Classification and/or Status

Spatangoida, Paleopneustina, Paleopneustidae.

Monophyletic.
Remarks

Differs from Paleopneustes in having a shorter labrum that does not extend beyond ambulacral plate 2, and with ambulacral plate 6 at the rear of the episternal plates. Plesiozonus also has a marginal fasciole and traces of a peripetalous fasciole as adults which are lost in Paleopneustes.

The genus has been documented in admirable detail by Mortensen (1950) and David & De Ridder (1989).

De Meijere 1902. Tijdschr. Nederland Dierk. Ver. (2) 8, p. 12.

Mortensen, T. 1950 A monograph of the Echinoidea. V, Spatangoida 1. C. A. Reitzel, Copenhagen.

David, B. & De Ridder, C. 1989. Echinodermes: Echinides irreguliers. In J. Forest (ed.) Resultats des campagnes Murorstom, volume 4. Memoires du Museum national d\'Histoire naturelle (A) 143, 203-227.