8-legged scorpions, mites, ticks, spiders, daddy longlegs. Evolutionary relationships of the arthropods They are uncertain. There is strong evidence that the insects and crustaceans are closely related. The features of these animals are listed above . The group comprises the echinoderms and the chordates .
Seawater is taken into a system of canals and is used to extend the many tube feet .
These have suckers on their tips and aid the animal in attaching itself to solid surfaces. About 6,000 species - all of them marine. At its anterior end, it becomes enlarged to form the brain . In vertebrate chordates, it is replaced by a vertebral column or backbone long before maturity. These lateral outpocketings of the pharynx are matched on the exterior by paired grooves.