Distribution of frilled protractor muscles in derived “regular” sea urchins.

A total of 49 echinacean (Echinoidea: Echinacea) species were analyzed by MRI, but this table also lists those genera for which no data are yet available. Representative species from all other sea urchin taxa that possess a lantern, and which have previously been analyzed by MRI (i.e., Cidaroida, Echinothurioida, “Diadematoida”, Pedinoida, Salenioida, Clypeasteroida), do not have frilled protractor muscles. See [54] for a full list of sea urchin species analyzed using MRI. Taxonomic arrangement of species according to Kroh & Mooi [83]. n/a = not available.