The Echinoid Directory

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Key to the genera of Strongylocentrotidae 1a. Ambulacra with four pore-pairs to a compound plate, forming vertical series. Hemicentrotus 1b. Ambulacral plates with between 5 and 10 pore-pairs to a compound plate. Go to 2 2a. Globiferous pedicellariae with paired lateral teeth and long muscular neck. Loxechinus 2b. Globiferous pedicellariae without lateral teeth and without muscular neck. Go to 3 3a. Ambulacra gradually narrowing towards peristome on oral surface; test thin. Allocentrotus 3b. Ambulacral zones expanded adorally; broader than interambulacral zones at peristome edge. Go to 4 4a. Buccal notches sharp with well developed tag. Pseudocentrotus 4b. Buccal notches feeble, hardly indenting the peristome and without tags. Go to 5 5a. Primary spines and tubercles large; spines with extensive median labyrinthic zone. Mesocentrotus 5b. Primary spines and tubercles not large; spines with well developed radial ridges. Strongylocentrotus