The Echinoid Directory

Key to the genera of Trigonocidaridae


1a. Apical disc with single tubercle on inner edge of othewise smooth genital plates. Trigonocidaris	1b. Apical disc tuberculate, usually with a ring of tubercles surrounding the periproct. Go to 2

2a. Test without any obvious pitting or sculpting. Prionechinus	2a. Test with pitting and/or epistromal sculpting of the test. Go to 3

3a. Secondary tubercles on coronal plates dense and uniform; ornament confined to small radial bars and pits around the primary tubercle. Genocidaris	3b. Secondary tubercles sparse and heterogeneous, intersperced with epistromal ridges. Radial ornament around primary tubercles. Go to 4

4a. Marked reduction in size of primary tubercles above the ambitus; epistromal ornament with strong vertical component linking tubercles dominates aboral plates. Scolechinus	4b. Primary tubercles not markedly smaller above ambitus; aboral plates not dominated by coarse epistromal ornament. Go to 5

5a. Pore zones offset in triads. Go to 6	5b. Pore zones uniserial or in weak arcs throughout. Go to 7

6a. Epistroma in the form of zig-zag vertical ribs and grooves. Goniosigma	6b. Epistroma in the form of reticulate ribs and grooves surrounding primary tubercle. Javanechinus

7a. Ambulacral plates with primary tubercles linked by zig-zag perradial ribs; no secondary tubercle. Leptopleurus	7b. Ambulacral plates with primary tubercle and smaller secondary tubercle immediately above and perradial to it. Go to 8

8a. Plates densely tuberculate. Ornament confined to pits around primary tubercles. Primary tubercles non-crenulate. Ortholophus	8b. Plates sparsely tuberculate aborally; ornament consisting of sparse radial bars around primary tubercles. Primary tubercles weakly crenulate. Go to 9

9a. Plate ornament of reticulate epistroma highly developed. Cryptechinus	9b. Plate ornament restricted to sparse radial bars around primary tubercles. Asterechinus