268 



SYSTEMATIC ZOOLOGY 





Auiphioxits lanceolatus (Fig. 280) is a more or less fishlike little 

 animal, about five centimeters long, exclusively marine, which 

 lives buried vertically in the sand in relatively shallow water on 

 tropical and temperate shores. In Europe it has been found 

 in the Mediterranean, the English Channel, and the North Sea, 

 and in North America along the southern portion of the eastern 

 coast of the United States and at Bermuda ; it also lives on many 

 shores in the Pacific Ocean. 



The body is somewhat compressed laterally and pointed at 

 both ends. At the anterior end on the ventral side is the 

 mouth, surrounded by a circle of bristlelike processes called 



A 



mtpL 



atrp ventfr 



or.h-cL 



mj/om eforsfr 



dorsf 



cir ' 



' or.hd 



jrov 



mlpl 



atrp 



lentfr 



yentf art 



cdf 



FIG. 280. Amphioxus lanceolatus. A, ventral aspect; B, side view. at), anus; atrp, atrial 

 pore; cd.f, caudal fin; cir, cirri; dors./, dorsal fin; dors./.r, dorsal fin-rays; gon, gonads; 

 mtpl, metapleure; myom, myomeres; nch, notochord ; or.hd, oral hood; vent.f, ventral fin ; 

 vent.f.r, ventral fin-rays. (After Kirkaldy, from Parker and Haswell's Manual.) 



cirri. Along the dorsal side of the body for its entire length 

 is a slight elevation, the dorsal fin, which is directly continuous 

 with a somewhat greater caudal or tail fin about the posterior 

 end of the body. On the ventral side of the body there is no 

 unpaired fin on the anterior two thirds, but instead two longitu- 

 dinal folds placed somewhat laterally ; at the posterior end of 

 these folds is an opening on the median line, called the atrial 

 pore, and from this an unpaired median ventral fin runs back- 

 ward to become continuous with the caudal fin. Some distance 

 posterior to the atrial pore is the anus, placed slightly to the 

 left of the median ventral line. 



Internally (Fig. 281) there is a well-developed chorda dorsalis 

 extending the entire length of the bodv, and dorsal to this is 

 the rodlike central nervous system, the neural tube, the anterior 



