Sea Urchins are a marine invertebrate occasionally mentioned in the How to Train Your Dragon Book series.
Sea Urchins (Class Echinoidea) are invertebrates found in salt water around the world in most marine habitats. They are roughly spherical with some sort of protective spines and five-fold symmetry in their adult stage. Sea urchins start off as eggs released into the water and are fertilized by sperm floating in the water. The fertilized eggs develop into a ball of cells (blastula), then develop further into a larvae called an echinopluteus. Finally the larvae sink to the bottom of the sea, having already started developing plating, and metamorphose into the spiny adult form. Most sea urchin species are toxic to some extent, but only a few are toxic enough to harm a human.
Sea Urchins do not have a direct function in the Book series, except as a descriptor. In actuality however, sea urchins are prized food items in many cultures. Typically the five orange-colored gonads in each urchin are eaten, raw or cooked.
An image of a sea urchin appears at the end of the book along with the image of Alivin the Treacherous' hand hook.
|“||For a long time she spun round in wobbly circles, like a confused sea urchin.||”|
|— Book 3|
Also in Book 3, Hiccup's hairs on the back of his neck again stand up like sea urchin spines. A previous description was in Book 1.
|“||Two enormous, masked Kidnappers crashed into the room with yells that froze the blood and made the hairs on Hiccup's head stand up like the spines on a sea urchin.||”|
|— Book 3|