.anterior dorsal fin 



posterior dorsal fin 



operculum 



caudal fin 



nasal tube 



LATIMERIA 



pectoral fin 



anal fin 



pelvic fin 



Figure 2-6. The living fossil tatimeria, a coelacanth crossopterygian. 



the anal fin. There are two pairs of lateral fins. These are 

 long, slim, fleshy structures with slight webbed margins. 



The lateral-line system is indicated on the head by grooves 

 or lines of openings. The lateral line of the body is distinct 

 and there is an indistinct ventral line extending back from 

 below the pectoral fin to just in front of the pelvic fin. From 

 here it appears to pass above the pelvic fin. 



Neoceratodus resembles Protopterus in many details. The 

 cycloid scales covering the body and the back of the head 

 are very large. The fins have much heavier, broader basal 

 lobes. The dorsal, caudal, and anal fins are continuous as 

 in Protopterus. The nasal or narial openings lie inside the 

 margin of the upper jaw; the more posterior one lies inside 

 the mouth. 



Amphibians 



Necturus and Cryplohranchus are la.'ge American salaman- 

 ders, both presumed to be neotenic forms; that is, they 



lateral sensory line 



retain larval features as adults (Figure 2-8). They are dorso- 

 ventrally flattened with relatively small limbs. The anterior 

 limb has four fingers, the posterior five; in Necturus the pos- 

 terior limb has only four. Each digit has a terminal pad of 

 skin. 



The head is broad and flat, the mouth is large with soft 

 fleshy lips. Necturus has an extensive opercular fold joined 

 across the ventral midline with that of the other side. These 

 folds are also fused to the isthmus. At the upper margin of 

 the opercular fold are the three large external gills, and 

 inside of the fold are the two openings between branchial 

 arches. In Cryplohranchus there is only a single branchial open- 

 ing in the fleshy lateral margin of the head. 



The body is covered with a smooth skin that has many 

 folds, and with many irregular lumps. The caudal fin extends 

 far forward above and below the fleshy tail. The cloacal 

 opening lies just behind the posterior pair of limbs. The lat- 

 eral-line organs are apparent as small bumps on the skin, 

 usually with a white tip. 



PROTOPTERUS 



NEOCERATODUS 



Figure 2-7. General oppearance of two of the living lungfishes. 



LIVING REPRESENTATIVE VERTEBRATES • 27 



