ORDER CHONDROSTEI — THE STURGEONS 21 



Order CHONDROSTEI 



THE STURGEONS 



Skeleton chiefly cartilaginous, the vertebral column entirely so; vertebrae 

 simple, acentrous, the notochord being persistent; fins without spines; ven- 

 tral fins abdominal; a mesocoracoid arch present; opercular series repre- 

 sented by an operculum only; maxillary present; air-bladder simple, with a 

 well-developed duct. Large fishes of the seas and fresh waters of northern 

 regions. A single living family. 



Family ACIPENSERIDiiE 



THE STURGEONS 



Elongate, subcylindrical fishes, with the head covered with bony plates 

 united by sutures, and with the body armed with 5 longitudinal rows of 

 bony bucklers; skin of sides between bucklers roughened more or less with 

 small irregular plates or spine-tipped ossicles; skeleton chiefly cartilaginous, 

 the notochord persistent and the vertebrae imperfectly developed; ventral 

 fins abdominal, behind middle of body; dorsal and anal fins posterior; tail 

 heterocercal, its upper lobe covered with rhombic scales; pectorals placed 

 low; gills 4; spiracles developed in some species; an accessory opercular 

 gill; spiracular pseudobranch small or obsolete; no branchiostegals; an 

 operculum and an interoperculum present; no suboperculum or preoperculum ; 

 nostrils double, in front of eye; lateral line present, concealed, traversing 

 the interior of the lateral bucklers; eyes small; optic nerves forming a chiasma; 

 mouth inferior, protractile, with thickened papillose lips; four barbels in a 

 transverse series on lower side of snout in front of mouth; no teeth except 

 in very young; stomach without bhnd sac; rectum with a spiral valve; pan- 

 creas divided into pyloric appendages; air-bladder simple, connected with 

 oesophagus by a duct; arterial bulb with several pairs of valves. 



Sturgeons are widety distributed in the seas, estuaries, and 

 rivers of Europe, Asia, and America, south of the arctic circle, 

 most species being anadromous— that is, hving part of the time 

 in salt water and ascending rivers to spawn, as do the salmon and 

 the shad. About 10 species of the genus Acipenser are found 

 along the coasts and in the seas and rivers of Europe and Asia, 

 being most abundant in the Black Sea, the Azov, and the Cas- 

 pian. Five species are found in North America, two on the 

 Atlantic coast, two on the Pacific coast, and one in the Great 

 Lake region — one of the Atlantic species (A. sturio) frequenting 



