Starfish are from the family in the animal kingdom called the echinoderms. There are several species of starfish and their 'arms' are more properly called rays. Most species of five rays, but some can have four and some have nine. Some species have a variable number, but always four, five or nine. Pycnopodia helianthoides, the sunflower star starts with around 9 rays and then add more as they grow. Adults usually have over 20.
If a starfish loses one of its rays, it can quite often regenerate its tissue completely to form a new one. Usually, regeneration is only possible if the central part of the body, the part that doesn't belong to the separate rays, is intact. Bizarrely, though, there are some species that can regenerate everything. Starfish from the Linckia species can be torn apart and a new starfish will grow up from each of the mangled fragments.
The span of a starfish varies according to the species ~ the smallest are about 1 inch across from ray end to ray end and the largest are a whopping three feet.
If a starfish loses one of its rays, it can quite often regenerate its tissue completely to form a new one. Usually, regeneration is only possible if the central part of the body, the part that doesn't belong to the separate rays, is intact. Bizarrely, though, there are some species that can regenerate everything. Starfish from the Linckia species can be torn apart and a new starfish will grow up from each of the mangled fragments.
The span of a starfish varies according to the species ~ the smallest are about 1 inch across from ray end to ray end and the largest are a whopping three feet.