The Echinoid Directory

• Apical disc dicyclic.
• Test circular in outline; depressed in profile.
• Ambulacral plating trigeminate with pore-pairs forming vertical band.
• One large primary tubercle to each ambulacral and interambulacral plate. Secondary tubercles developed on either side and smaller tubercles common.
• Buccal notches small; phyllodes not developed.
• Spines stout and pointed; less than half the test diameter at their longest..

?Miocene to Recent; Eastern Atlantic and Mediterranean.

Echinus miliaris Muller, 1771, p. 108, by subsequent designation of Lambert & Thiery, 1910, p. 239.

• P. miliaris (Muller, 1771); Recent, Atlantic.
• P. microtuberculatus (Blainville, 1825); Recent, Mediterranean.
• ? P. praecursor Ortmann, 1904; Miocene, Patagonia.

Camarodonta; Echinoida; Parechinidae.

?Paraphyletic.

The primitive nature of the globiferous pedicellariae and simple trigeminate ambulacral plating place Psammechinus as plesiomorphic to most other Echinoida discussed here. It differs from Paracentrotus in having trigeminate rather than polygeminate ambulacra, and from Parechinus in having the arcs of pore-pairs more vertical such that the pore-pairs do not define vertical series. In comparison to Gracilechinus the test is very much more densely tuberculate. Finally Echinus and Sterechinus have tubercles on every second or third ambulacral plate only. Isechinus is very similar but has better developed secondary tubercles in both ambulacra and interambulacra.

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. 1943. A monograph of the Echinoidea Part III, 3. Camarodonta II. C. A. Retzel, Copenhagen.