Survey of the Animal Kingdom 329 



Subphylum 3 — Cephalochordata (sef a lo kor -da' ta) (Gr. kephale, head; 

 chorde, chord). — These marine animals have small, slender, elongate "fishlike" 

 bodies which are distinctly segmented. The permanent dorsal notochord and nerve 

 cord extend from the head to the tail (entire length of body). Many permanent, 

 paired gill slits (pharyngeal clefts) are present in the pharynx. No cranium, 

 jaws, vertebrae, or paired appendages. 



Example: Amphioxus or lancelet (Branchiostoma sp.) (Fig, 142). 



Fig. 144. — Representatives of the class Elasmobranchii, phylum Chordata (not 

 drawn to scale). A, Spiny dogfish shark (Squalus acanthias) ; B, sawfish (Pristis 

 antiquorum) ; C, hammer-head shark {Sphyrna zygaena) ; D, Southern sting ray 

 {Dasyatis americana) , common in the Gulf of Mexico. 



Subphylum 4 — Vertebrata (vur te -bra' ta) (L. vertebratus, jointed) or Cra- 

 niata (Kra ni -a' ta) (Gr. kranion, cranium or head). — All vertebrates have a noto- 

 chord at some stage of development. This is replaced by an axial skeleton com- 

 posed of vertebrae in higher species. Both the axial and appendicular skeletons 

 are internal. They all have a coelom (true body cavity) and are bilaterally 

 symmetrical. The body is divided into head, thorax, and abdomen, A hollow 



