4 LABORATORY DIRECTIONS 



Although considered a vertebrate, the lamprey has very 

 rudimentary vertebrae which consist merely of minute cartilages 

 on either side of the notochord. 



Shark — Class Elasmobranchii 



The elasmobranchs are the cartilaginous fishes. By some 

 they are classified as belonging to an order of Pisces; others 

 think they are sufficiently diverse to form a separate class by 

 themselves. 



The mouth is ventral in position. At each corner is an oro- 

 nasal groove, extending toward, but not reaching the nostril. 

 The sharply pointed teeth are arranged in several rows. They 

 are really modified scales. 



The nares or nostrils on the ventral side of the head are mere 

 pits and have no connection with the mouth. The opening of 

 each nostril is wholly or partly divided by a projecting flap of 

 skin. 



The eyelids are not movable. Behind the eyes are a pair of 

 spiracles. These are modified gill slits and contain small gills. 

 Do they open into the mouth cavity ? There are five gill slits 

 on each side, each with its own gill cover. Do the gill slits 

 connect with the mouth cavity ? 



The cloaca is a small cavity on the ventral side about two- 

 thirds the way back toward the tail. It is the common outlet 

 of both digestive and urogenital systems. Within it is the 

 urogenital -papilla with the urogenital pore at its tip. 



The fins consist of two dorsal fins, a caudal fin, paired pectoral 

 fins, and paired pelvic fins. An anal fin just posterior to the 

 cloaca is present in most fishes, but is absent in this species of 

 shark. Male elasmobranchs may be distinguished from females 

 by the presence in males of a clasper on the inner margin of each 

 pelvic fin. 



A sense organ, the lateral line, extends as a shallow groove 

 along each side of the body. On the dorsal side of the head are 

 numerous small pores which are part of the lateral line system. 

 On the ventral side of the head are similar pores not directly 

 connected with the lateral line organs. These are the ampullae 

 of Lorenzini and are probably sensory in function. Do they 



