CLASS MARSIPOBRANCHII 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, eehshaped 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 Petromyzonidw , which follows. 



Family PETROMYZONlD^E 



(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 by 

 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 not 

 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 and resting on papillae; 

 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 cascal appendages, pancreas, 

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

 tive outlet peritoneal, the eggs small and falling into the abdominal 

 cavity; young undergoing a metamorphosis, the larvae being blind 

 and burrowing in the mud or sand. 



(2) 



