72 



PLATYHELMINTHES 



Natural History 



Class I. Turbellaria. — Turbellaria are unsegmented worms, 

 living in fresh, brackish or salt water or moist earth. They are 

 elongated and flat, and antero-posteriorly differentiated, with two 

 prominent eyes. They vary in color from transparent to red, gray, 

 brown and almost black. Some {Planaria maculatd) are spotted. 

 Locomotion is by undulation and by means of cilia. (Figure 31.) 



5ra/n 



Eye 

 ■ Ovory 



YolR (glands 



In^esfine 



-Lofero/ nerve 



Vos deferens- 



Genital pore' 



1- Pharynx 



~Infes//'ne 



■ Mouth 

 Penis 



Oviduct 

 Vocjina 



Fig. 31. A Planarlan worm. (From Lankester, after von Graff.) 



Planarians vary in size, but do not usually exceed one-half inch 

 in length. Some greenhouse and tropical tree planarians are over a 

 meter in length. They are widely distributed in fresh or salt water, 

 but only a few are pelagic. They usually live free but are sometimes 

 found in a state of commensalism, as for example Bdelloura, which 

 lives in the gill books of the horseshoe crab, Limidus. Planaria are 

 dorsiventrally differentiated and have eye-spots and ganglia. The 

 lappets, antero-laterally situated, are olfacto-gustatory organs. 

 The ectoderm is ciliated, often glandular, and equipped with rhab- 

 dites, rod-like bodies capable of being discharged on irritation. 

 Turbellaria with a branched digestive tract are called Dendrocoela, 

 and those with a straight digestive tract are called Rhabdocoela. 



