Close-up view of a young sea star or starfish, demonstrating two of the key anatomical features of echinoderms, the phylum to which they belong. The first is the pentaradial (five-way radial) symmetry that gives it its characteristic star shape, which is highly unusual. This symmetry means that, unlike most ‘higher’ animals, the sea star has no head or tail end -simply an oral side, facing down, and an aboral side facing up from the sea floor. The second is the tube feet we can see extending from the main body. These are filled with water by the water vascular system, a special network of canals and vessels in the sea star’s body, inflating them and allowing the animal to move around. Each foot has a specialised sucker at the tip containing many sensory cells. Recent research has even suggested that their feet are sensitive to light and could be used to help guide echinoderm movement. Echinoderms play an important role in many evolutionary and developmental research projects, as they are fairly closely related to vertebrates – surprising when you look at them!
Image courtesy of Bruno Vellutini and the Nikon Small World competition.