• ACANTHODIANS: an extinct class of fish living from Early Silurian to Permian; first fish showing jawlike structure (also known as spiny sharks)
• ACTINOPTERYGII:  subclass of Osteichthyes characterized by bony fin supports; commonly called ray-finned fish (ex: tuna, salmon, trout)
• AGNATHA: class of jawless fish from Late Cambrian to Recent (ex: ostracodrem, hagfish, lamprey)
• CHONDRICHTHYES: a class of fish; characterized by cartilaginous skeleton; includes sharks, skates, rays and chimaeras
• DENTICLE: placoid scales, teeth-like scales made of calcium phosphate; they help channel  water reducing friction
• DIFFERENCE BETWEEN SHARKS AND FISH

Feature	Fish	Sharks
"skin"	scales	denticles
gill	one gill cover (bonelike operculum)  gills on both sides of head	five to seven paired gill slits gills on both sides of head
swim bladder	yes	no
copulation	no	yes and no
mouth position	terminal	ventral
tooth attachment	attached to jaw sockets	not firmly attached
tail shape	symmetrical extension of backbone	asymmetrical - positioned where vertebrae end

• ELASMOBRANCH: subclass of Chondrichthyes containing Sharks and Rajiformes
• EXTANT:  living; present
• HOLOCEPHALAN: subclass of Chondrichthyes containing Chimaeriformes
• OSTEICHTHYES (BONY FISH): a class of fish containing two subclasses (Actinopterygii and Sarcopterygii); characterized by skeleton of bone
• OSTRACODERMS:  an early member of the class Agnatha, now extinct
• PLACODERM: an extinct armored fish; Late Silurian to Permian
• SARCOTERYGII:  subclass of Osteichthyes characterized by articulated fleshy fin attachment; commonly called lobe-finned fish (ex: lungfish, coelacanth)

bharris@chat.carleton.ca