362 



THE ANIMAL KINGDOM 



Proboscis 



Mouth- 

 Collar 



Anterior region: 

 oF trunk 



Gill slits 



Coelomj 



Glomeralus 



Stomochorci 



Proboscis pore. 

 Collar ne.rv(Z. 



Coelonrz, 



Coelom: 



"La-terad fold 



Figure 1 9.3. Class Enteropneusta (genus Saccoglossus). Left, external view showing 

 external features (after Bateson). Right, a diagrammatic section through the anterior part 

 of the body showing some of the internal organs. A lateral fold subdivides the pharynx 

 into a ventral channel along which the sand passes and a dorsal channel containing the 

 gill slits. 



evski (Fig. 19.3) of the Atlantic coast. These burrow in sandflats near the 

 low tide line, living in semipermanent tunnels lined with a mucous 

 secretion. The mouth, which apparently cannot be closed, lies ventrally 

 between the proboscis and the collar. As the worm burrows, much of 

 the sand is swallowed. In the pharynx excess water passes out through 

 the gill slits and the sand passes down a long intestine. All of the nourish- 

 ment of Saccoglossus comes from organic debris in the sand. Eventually 

 the sand is eliminated through a terminal anus, often piling up in long 

 coils aroimd openings to the burrows. 



The yellowish pink proboscis of Saccoglossus is longer than that of 

 most enteropneusts. The junction of proboscis to collar is a narrow 

 stalk. The proboscis pore that opens into the coelomic cavity of the 

 proboscis is located dorsally at the posterior margin of the proboscis. 

 The reddish collar overlaps the stalk in front and the trunk behind. Its 

 coelomic cavity opens on the sides through a pair of ducts that end at 

 the first pair of gill slits in the trunk. Saccoglossus burrows by inflat- 

 ing the collar against the tunnel wall, pushing the deflated proboscis 

 forward, inflating the proboscis, deflating the collar and pulling the body 

 forward. 



The trunk is divisible into three regions. In the anterior part nu- 



