Jain Biology: 6. Phylum Annelida:

These arc referred to as the true worms; they are triploblastic, bilaterally symmetrical animals; most of the organs are repeated in all of a large number of segments; digestive tract is complete; circulatory system is of the closed type; respiratory pigment—haemoglobin is dissolved in the plasma; excretory organs are in large numbers in most segments; nervous system consists of a ganglonated nerve cord connected to a pair of ganglia (brain). Many of them have the capacity of regeneration when cut into pieces. Some common exam-pies: Earthworms—mostly found in damp soil amongst decaying vegetation; cylindrical body is divided into 120-125 segments; they are bisexual. Leech—mostly live in fresh water; some of them are blood-sueking ectoparasites on other animals including men. A medici-nal leech (Hirudo) is used occasionally to suck blood from inflamed parts.