Leech is an Annelida, and has ventral central nervous system which consists of nerve ring, and a solid, double, mid ventral nerve cord with ganglia. Chameleon is a reptile, possessing pharyngeal gill slits during its embryonic development, and are later replaced by lungs. Scorpion is an Arthropoda, having dorsal heart. Octopus, a mollusc do not possess post anal tail. It is a characteristic feature of mammals. Related Theory The arthropod nervous system consists of a dorsal brain and a ventral, ganglionated longitudinal nerve cord (primitively paired) from which lateral nerves extend in each segment. The system is similar to that of annelid worms, from which arthropods may have evolved.