Sterechinus

Members of the genus Sterechinus have compound ambulacral plates that are trigeminate (composed of three elements). These plates have a primary tubercle articulating with a spine on the middle element, a small secondary tubercle in the interambulacral groove on one side of it and 3 pairs of pores on the other. The tube feet are connected to these pores in the living animal and the pore pairs are arranged in a vertical arc. The sutures between the plates are deeply indented. The area of narrow plates around the mouth is small and the buccal notches are shallowly grooved.^[2]

The type species of this genus is Stirechinus scillae which was first described from a fossil by Pierre Desor in 1856. Stirechinus scillae lived from the Late Miocene to the Plio-Pleistocene and further fossils have since been found in France, Sicily and Malta. None of the fossilized urchins so far discovered had any apical plates.^[2]

Since then, other members of the genus have been described, all from the waters around Antarctica. The World Register of Marine Species lists the following extant species in the genus:^[1]

• Sterechinus agassizii Mortensen, 1910
• Sterechinus antarcticus Koehler, 1901
• Sterechinus bernasconiae Larrain, 1975
• Sterechinus dentifer Koehler, 1926
• Sterechinus diadema (Studer, 1876)
• Sterechinus neumayeri (Meissner, 1900)