CLASS MARSIPOBRAXCHII THE HAGFISHES AND LAMPREYS 



Class MARSIPOBRANCHII 



(THE HAGFISHES AND LAMPREYS) 



Skull imperfectly developed, not separate from the vertebral col- 

 umn; no true jaws, no limbs, no shoulder girdle, no pelvic elements, 

 and no ribs; gills in the form of fixed sacs, purse-shaped, without 

 branchial arches; nostril single. Naked, eel-shaped animals, with a 

 suctorial mouth, inhabiting both fresh and salt water. 



Order HYPEROARTII 



(THE LAMPREYS) 



Nasal duct not penetrating the palate. This order is equivalent to 

 the single family Petromyzonidce, which follows. 



Family PETROMYZONIDiE 



(the lampreys) 



Limbless, eel-shaped, naked-skinned vertebrates of parasitic or 

 modified parasitic habit, with a circular suctorial mouth furnished 

 with cusp-like teeth suited for rasping; body subcylindrical forward, 

 vertically flattened behind; skeleton wholly cartilaginous; skull im- 

 perfect, continuous with the vertebral column; no shoulder girdle, no 

 pelvic elements, and no ribs; vertical fins with feeble rays, ordinarily 

 continuous around the tail ; gills 7 in number on each side, in the form 

 of fixed sacs, and without true branchial arches, being supported l>v 

 a wicker-like arrangement of cartilages known as the "branchial 

 basket"; gill-openings separate, arranged in a row along each side of 

 neck; nostril single, median, in front of eyes, the nasal tube in it 

 penetrating the palate; mouth suctorial, without true jaws; interior 

 of buccal funnel (mouth disk) armed with horny teeth or tooth-like 

 tubercles, these being simple or multicuspid ami resting on papilla?; 

 teeth immediately above and below oesophagus (on the so-called 

 "tongue") more or less specialized ; heart without arterial bulb; ali- 

 mentary canal straight, simple, without caecal appendages, pancrea 

 or spleen; intestine with a spiral valve; air-bladder wanting; gene , 

 tive outlel | the egg -mall and falling into the abdominal 



cavity; young undergoing a metamorphosis, the larvae being Mind 

 and burrowing' in I'm mud or sand. 



