CLASSIFICATION OF VERTEBRATA 



SUB-PHYLUM CRANIOTA 



With cartilaginous (unless ossified) cranium, arches and 

 blocks of the axial skeleton. 



Super-CLASS CYCLOSTOMATA 



CYCLOSTOMATA, Richards = MARSIPOBRANCHII, 

 Bonaparte = MONORHINA, Haeckel 



Without visceral arches transformed into jaws, and without 

 paired limbs. 



Nasal tube unpaired, median. 



Liver a compact gland. 



Pronephros persistent. Gonomeres fused. 



With bag-shaped gill-pouches or gill-slits. 



Mouth suctorial. 



I. CLASS MYXLNOIDES 

 = HYPEROTRETA, Mueller 



The Myxinoids are the lowest living true vertebrates. 

 Their hypophysial duct still communicates with the mouth- 

 cavity, and this communicates with the unpaired rhinal open- 

 ing. If the latter condition is the primitive one, then 

 Fuerbringer (1897) is justified in establishing for the Myxin- 

 oids the term " Distoma," creatures which still possess the 

 palaeostoma and the neostoma of Kupffer. 



The segmental nephric ducts remain separate, and open 

 separately into the long, lateral archinephric ducts. 



Ear with oue semicircular canal only. — Marine, parasitic, 



Bdcllostomidae. Gill-pouches with separate external and 

 internal openings. 



Bdellostoina , Heptatrema, Polytrema. 



Myxinidae. The external openings of the gill-pouches are 

 produced into long canals with one posterior opening. 



Myxine, Gastrobranchus. 



