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PHYLA OF LESSER SIGNIFICANCE 



Photo by Winchester 



Fig. 18.4. Arrow worms. 



Phylum — Chaetognatha 



This phylum includes a small number of species, all of which are ma- 

 rine. They are slender transparent worm-like creatures that are given 

 the common name of arrow worms. 



Phylum — Nemertea 



This is another phylum of worms which are almost all marine and 

 not commonly seen. They are of some biological significance, however. 

 They are sometimes placed in the Platyhelminthes, yet they have a di- 

 gestive tube with two openings and a series of three blood vessels for 

 circulation that seem to set them in advance of the flatworms. They 

 are commonly called proboscis worms. 



Phylum — Onychophora 



This phylum includes a single genus, Peripatus, which bears many 

 characteristics of the annelids, but it is also similar to the most advanced 

 phylum of the invertebrates, the Arthropoda. This creates a problem 

 of classification which most authorities feel is best solved by placing it in a 



