A 



CHAPTER 14 



i 1 



Oil 



Miscellaneous 

 Minor Phyla 



NUMBER of groups of animals are con- 

 sidered together here because their relation- 

 ships to other animals and to each other are 

 rather uncertain. Tliis chapter is something 

 of an invertebrate catchall; it contains sev- 

 eral groups that in prehistoric times were 

 large, but at present are represented by 

 relatively few types. However, an introduc- 

 tion to general zoology would be incomplete 

 without at least a look at these interesting 

 though highly specialized groups. 



PHYLUM NEMERTINA 



(RHYNCHOCOELA)- 



RIBBON WORMS 



The members of the phylum are called 

 ribbon worms because they are long and 

 flattened dorsoventrally (Fig. 86). They 

 range in length from less than an inch to 

 over 90 feet. Most live in the sea, but a few 

 inhabit fresh water and land. 



The most important anatomic features of 

 the nemertines are the presence of (1) a 

 long retractile proboscis, which lies in a 

 proboscis sheath just above the digestive 

 tract and may be everted and used as a 

 tactile, and a defensive organ; (2) a blood 

 vascular system, usually consisting of a me- 

 dian dorsal and two lateral trunks; and (3) 

 a complete digestive tract with both mouth 

 and anal openings. The circulator}' system 

 is encountered here for the first time. 



The nemertines resemble the free-living 

 flatworm or Turbellaria in being bilaterally 

 symmetrical, in having flame cells, unseg- 

 mented and contractile bodies, and in lack- 

 ing a true coelom and respirator}' system. 

 However, they differ from the flatworms in 

 that they have a complete digestive system 

 with mouth and anus, a functional cir- 

 culatory system, a less complex reproduc- 

 tive system, and they are usually dioecious. 

 Nemertines feed on other animals, both 

 dead and alive. They live, as a rule, coiled 

 up in burrows in mud, sand, or under stones, 

 but some of them frequent patches of sea- 



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