9); the canines are small or absent; the cheek-teeth have bluntly tuberculate or transversely-ridged crowns in most cases; and the hind-feet are syndactylous.
The tuberculate roots are edible.
In diameter, with a thick minutely tuberculate rind, the inner lining of which is sweet, and a watery acidulous pulp. It has long been cultivated in China and Japan, and was introduced to Europe in 1846 by Mr Fortune, collector for the London Horticultural Society, and shortly after into North America.
- Ambulacrals simple, each with one or two pores, which sometimes pass between rather than through the plates, in 2 columns; interambulacrals, unior multi-tuberculate, in numerous (say io or more) columns, none passing on to peristome; mouth central with jaws, no external gills or sphaeridia; position of anus doubtful, acyclic, i.e.
- Ambulacrals sometimes compound, with one or two pores to a plate, some dorsal podia begin to assume respiratory function; interambulacrals multi-tuberculate, none resorbed; mouth central, with jaws weak or wanting, with external gills and sphaeridia; anus exocyclic. Families: Pygasteridae, Discoidiidae, Galeritidae, Conoclypeidae; Jurassic to Recent.
In some species certain of the legs bear on their ventral sides furrows with tumid lips and lined by smooth non-tuberculate epithelium; they are called coxal organs, and it appears that they can be everted.