The Echinoid Directory

Key to the families of Micrasterina


1a. Episternal plates (in red) paired and opposite. Subanal fasciole (where developed) crossing middle of episternals. Apical disc ethmolytic. Go to 2	1b. Episternal plates (in red) distinctly staggered at rear. Subanal fasciole (where developed) crosses sternal-episternal boundary. Apical disc ethmophract. Micrasteridae

2a. Labral plate (yellow) elongate and wedge-shaped; extending to at least half way down the second ambulacral plate. Go to 6	2b. Labral plate anvil-shaped; wider than long; not extending beyond the first ambulacral plate. Go to 3

3a. Anterior ambulacrum flush and narrow; without specialised funnel-building tube-feet and enlarged pore-pairs. Go to 4	3b. Anterior ambulacrum sunken and with specialised aboral funnel building tube-feet and enlarged pore-pairs. Brissopsidae

4a.Petals well developed; always narrow and parallel-sided. Peripetalous fasciole always present. Go to 5	4b. Petals poorly developed or absent. No peripetalous fasciole. Palaeotropidae

5a. Petals narrow and parallel-sided. Brissidae	5b. Petals distinctly bowed or lanceolate with wide interporal zone. Spatangidae