PHYLUM III. 

 VERMES. (The Lowek Worms.*) 



Worms of primitive structure and often of small size, usually without 

 paired locomotory appendages or a distinct head, and with non-metameric 

 and often permanently ciliated bodies. The animals are usually sluggish 

 of movement and in very many cases either sessile or parasitic. 



The Vermes form a polymorphic group of animals, the eight subphyla 

 of which do not necessarily bear a close genetic relationship to one another. 

 They, however, have many structural features in common and many of 

 the classes bear a definite relation to the trochophore larva which justifies 

 the placing of them in a common group. This would rank immediately 

 beneath the annelids and the other groups in which the trochophore 

 represents an ancestral form. 



The class Vermes, as formed by LinnaBus, included all invertebrate 

 animals except arthropods. Lamarck divided the invertebrates into several 

 classes, of which one was Vermes, including in it both the unsegmented 

 and segmented wonns. This arrangement, although it has been followed 

 by Claus, Hertwig, and other modern authors, is not now usually adopted, 

 and the Vermes, when used as the name of a phylum, generally include 

 the lower worms alone. 



The phylum contains 8 subphyla. 



Key to the subphyla of Vermes: 



Oi Animals mostly non-burrowing. 

 61 Animals mostly locomotory. 

 Cj Animals mostly not minute and very often parasitic. 



dj Flattened worms ; very many parasitic 1. Plathelminthes 



^2 Round and thread-like worms; often parasitic. .. .2. Nemathelminthes 

 C2 Animals minute and aquatic. 

 di Crown of cilia at forward end ; animals mostly in fresh water. 



3. Trochelminthes 



da No external cilia ; animals marine 7. Ch^tognatha 



?>2 Animals sessile. 



Ci Animals colonial 4. Bryozoa 



Co Animals not colonial. 



di Animals with a two-valved shell 5. Brachiopoda 



do Animals form tubes 6. Phoronidea 



Ca Marine worms which burrow in the sand and mud 8. Sipunculoidea 



* See "Vermes," by H. Pagenstecher and M. Braun, Bronn's Klassen und 

 Ordnungon des Thierreichs, Band 4, 1893. "Textbook of the Embryology of Inverte- 

 brates, Part I," by E. Korschelt and K. Heider, translated by E. L. Mark and W. M. 



155 



