BIOL 2003 Lecture Notes - Lecture 16: Agnatha, Gnathostomata, Holocephali
Chondricthyes
November 2, 2015
Chondricthyes – sharks and rays
• Part of gnathostomata
• Cartilaginous skeleton
• Placoid scales
• Claspers
• Groups: Elasmobranchii and Holocephali
New in gnathostomes:
• Jaws (and teeth)
o Derived from support arches
o Increases dietary diversity
• Paired fins
o Not found in most jawless fish
o New muscles associated with fin anatomy
o More maneuverability and mobility
o Cephalochorates were leading predators before sharks
• Stomach
o Store food to be digested
• Predation
o Need stronger swimming, better muscular physiology
Include all the major funding organs
o Brain: forebrain, midbrain and hindbrain
o Senses of vibration, balance and rotation acceleration
o Dorsal hollow nerve chord
o Gill slits
o Similar, recognizable heart
o Digestive system: stomach, intestine
o Kidney is elongated down the back
▪ Same nephrons although it looks very different
o Liver is connected to gut through circulation
o Pancreas – secretes digestive enzymes; secretes insulin/glucagon
o Spleen
Finding Prey: sensing vibration and electrical fields
• Sensory organs include well developed eyes and senses that do not work in air
• Sense organs are below the external surface that are in water connected organelles called lateral line
canals
• Vibration sensors – neuromast cells
• Electrical field sensors – nerves through jelly filled canal
o Derived from mechanical sensors
• Ectractoderms (jawless fish) may have been able to pick up electrical signals
• Both sensories found in gnathostomes
Jaws and Teeth (SHARKS):
• Row of teeth is a characteristic of all gnathostome
• Functional rows in front with developing teeth behind
• Creates a conveyor belt
• Every shark sheds many teeth over a lifetime – continuously replaces
• Great white – cerated teeth?
find more resources at oneclass.com
find more resources at oneclass.com
