CHORDATA 



Bilaterally symmetrical coelomate animals with a noto- 

 chord, dorsal and tubular central nervous system, and a 

 pharynx perforated by branchial clefts (gill slits). 



Subphylum 1. Protochordata. 

 Class 1. Hemichorda. 



The notochord is poorly developed and re- 

 stricted to the anterior end of the body. 



Order 1. Enteropneusta. 



Wormlike, with numerous branchial clefts, a 

 straight intestine, and a terminal anus. Body 

 divided into three regions — proboscis, collar, 

 and trunk. Development usually with a met- 

 amorphosis, the larva being known as a 

 tornaria. (Balanoglossus and Dolichoglossus.) 



Order 2. Pterobranchia. 



Tubicolous, with one pair of branchial clefts or 

 none, a U-shaped alimentary canal, and a dor- 

 sal anus situated near the mouth. Proboscis 

 flattened ventrally into a large "buccal disk," 

 its base covered dorsally by the collar which is 

 produced into two or more tentaculiferous 

 arms. Trunk short, prolonged into a stalk. 

 Reproduction by budding occurs. (Cephalo- 

 discus, Rhabdopleura.) 



Order 3. Phoronidea (doubtfully placed with the chor- 

 dates) . 

 Tubicolous with gregarious habits. The body 

 ends in a plume of ciliated tentacles ; the 

 alimentary canal is U-shaped. There is a 

 larva known as actinotrocha. (Phoronis.) 

 Class 2. Urochorda. 



The adult body is enclosed in a tunic or test, 

 and usually lacks a notochord; the central 

 nervous system is reduced to a simple ganglion. 

 With an atrial cavity and a pharynx perfor- 

 ated by from two to many gill clefts. There 

 is usually a tadpole-shaped motile larva which 

 possesses a tubular dorsal central nervous sys- 

 tem and a notochord restricted to the caudal 

 region. 



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