Sensory organs of the squid are located in the head region, much like in our bodies. Their brains are relatively large, and they can sense light, which gives them an advantage in hunting. That is what makes these worms special. Their segments are called metameres, and they allow the worms to have a fast response. The segmented body type help to control locomotion, and in addition to the nervous system, they also have muscles that run the whole length of the body, and muscles that circle around.
Annelids have some of the fastest reflexes in the animal kingdom.
Sea squirts are just one kind of Urochordate. When the adult is fully developed, there is no sign that a central nerve chord ever existed. Their curculatory system is composed of a heart with vessels, similar to what we have, except that in Urochordates body fluid can be pumped backwards and forwards through the body. This is also important to make sure that oxygen is equally transferred to all parts of the organism.