/THE PHYLUM CHOftDATA 33 



Sub-Phylum Tj~~Cephalochordata (Adelochorda) . 



This includes ,but a single family of fish-like creatures, of 

 which there are about twelve species v The type form is 

 1 Amphioxus (more correctly known as Branchiostoma) . 



Sub-PEylum II. Urochordata. 



Order 1. Larvacea (Appendicularia), free-swimming forms 

 with permanent tail. 



Order 2. Ascidiacea (Tunicates or Sea-Squirts), fixed forms 

 without tail in the adult. 



Order 3. Thaliacea (Salpians), free swimming forms with- 

 out tail in the adult. 



Hemichordata. 

 Order 1. Enteropneusta, including worm-like forms such 



as Balanoglossus. - 

 Order 2. Pterobranchiata, sessile, tube-dwelling forms 



Cephalodiscus and Rhabdopleura. 

 Order 3. Phoronidia, tubicolous forms Phoronis. 



Sub-Phylum IV. Vertebrata (Craniata). 



Class 1. Cyclostomata ' (round mouth eels): 



Class 2. Pisces (true fishes with jaws). 



Class 3. Amphibia (vertebrates with aquatic larvae, bu 



usually air-breathing in the adult condition). 

 Class 4. Reptilia (cold-blooded, air-breathing vertebrates} 

 Class 5. Aves (birds, feathered vertebrates). 



Class 6. Mammalia (beasts or quadrupeds) . 



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SUB-PHYLUM I. CEPHALOCHORDATA 



JThe Cephalochordata are considered first because their claims to 

 vertebrate relationship lire stronger than those of the other pro ver- 

 tebrate sub-phyla. They are rather small, marine, fish-like animals, 

 usually called "lancelets" on account of their sharply pointed ends. 

 Amphioxus was first described by Pallas in 1778. On account of its 

 resemblance to a slug it was given the name of Limax lanceolatus, the 

 implication being that it was a mollusk. In 1804 Costa, an Italian 

 naturalist, redescribed it as a fish, allied to the lampreys and hag- 

 fishes, and, because he erroneously diagnosed the oral tentacles qr/ x 



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