Sea urchin
Sea urchins or urchins () are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to . Their tests (hard shells) are round and spiny, typically from across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, and triggerfish.
Sea snake
Sea snakes were at first regarded as a unified and separate family, the Hydrophiidae, that later came to comprise two subfamilies: the Hydrophiinae, or true/aquatic sea snakes (now 16 genera with 57 species), and the more primitive Laticaudinae, or sea kraits (one genus, "Laticauda", with five species). Eventually, as just how closely related the sea snakes are to the elapids became clear, the taxonomic situation became less well-defined. Some taxonomists responded by moving the sea snakes to the Elapidae, thereby creating the subfamilies Elapinae, Hydrophiinae, and Laticaudinae, although the latter may be omitted if "Laticauda" is included in the Hydrophiinae. No one has yet been able to convincingly work out the phylogenetic relationships between the various elapid subgroups, and the situation is still unclear. Therefore, others opted to either continue to work with the older traditional arrangements, if only for practical reasons, or to lump all of the genera together in the Elapidae, with no taxonomic subdivisions, to reflect the work that remains to be done.
"*) Not including the nominate subspecies"