Flatworms

Taxonomic Classification

Kingdom:	Animalia
Subkingdom:	Eumetazoa
Clade:	ParaHoxozoa
Clade:	Bilateria
Clade:	Nephrozoa
Unranked:	Protostomia
Unranked:	Spiralia
Clade:	Rouphozoa
Phylum:	Platyhelminthes
Source: Integrated Taxonomic Information System

Flatworms are the simplest of the worm groups. There are roughly 20,000 species. Flatworms are found globally and can be free-living or parasitic. One of the best-known flatworms is the tapeworm.

Anthropogenic Drawbacks

Attribute	Cnidarians and Ctenophores	Platyhelminthes (flatworms)	More "advanced" bilaterians }}
Bilateral symmetry	No	Yes
Number of main cell layers	Two, with jelly-like layer between them (mesoglea)	Three
Distinct brain	No	Yes
Specialized digestive system	No	Yes
Specialized excretory system	No	Yes
Body cavity containing internal organs	No		Yes
Specialized circulatory and respiratory organs	No		Yes