What is "cake urchin"

Cake \Cake\ (k[=a]k), n. [OE. cake, kaak; akin to Dan. kage, Sw. & Icel. kaka, D. koek, G.kuchen, OHG. chuocho.]

1. A small mass of dough baked; especially, a thin loaf from unleavened dough; as, an oatmeal cake; johnnycake.

2. A sweetened composition of flour and other ingredients, leavened or unleavened, baked in a loaf or mass of any size or shape.

3. A thin wafer-shaped mass of fried batter; a griddlecake or pancake; as buckwheat cakes.

4. A mass of matter concreted, congealed, or molded into a solid mass of any form, esp. into a form rather flat than high; as, a cake of soap; an ague cake.

   Cakes of rusting ice come rolling down the flood.
   --Dryden.

   Cake urchin (Zo["o]l), any species of flat sea urchins belonging to the Clypeastroidea.

   Oil cake the refuse of flax seed, cotton seed, or other vegetable substance from which oil has been expressed, compacted into a solid mass, and used as food for cattle, for manure, or for other purposes.

   To have one's cake dough, to fail or be disappointed in what one has undertaken or expected.
   --Shak.

n. Any of the genus ''Clypeaster'' of echinoderms.