The Echinoid Directory

1a. Apical disc ethmophract.

1b. Apical disc ethmolytic.

2a. No occluded plates at ends of petals.

2b. Petals end with one or more occluded plates.

3a. Fascioles present in adults.

3b. Fascioles absent.

4a. Petals short (ending well before the ambitus) and sunken. Fascioles generally present.

4b. Petals long, parallel and more or less flush, extending almost to ambitus. Fascioles generally absent in adults.

5a. Single anterior fasciole (yellow) crosses plates 3 or 4 in the anterior interambulacra.

5b. Two fascioles present anteriorly; a marginal fasciole crossing plates 3 or 4 in anterior interambulacrum, and a peripetalous band crossing plates 6-8 (the two fascioles sometimes coalescing anteriorly).

6a. Fasciole bounding the ends of the anterior petals and crossing plate 5 in interambulacra 1b and 4a. On this plate the fasciole divides into a peripetalous band and a marginal (lateroanal) band, the latter partially or completely lost in some taxa.

6b. Fasciole crossing plate 4 in interambulacra 1b and 4a and generally passing at some distance beneath the ends of the anterior petals. On this plate the fasciole divides into a peripetalous band and a marginal (lateroanal) band, the latter partially or completely lost in some taxa.