Class Chondrichthyes

1
Class Chondrichthyes

• Subclass Elasmobranchii
• 8 orders of sharks
• Gill slits on side of head
• 1 order containing skates and rays
• Gill slits on ventral surface
• Subclass Holocephali
• 1 order containing ratfishes, chimaeras
• Only one gill slit

2
Skates and Rays

• Dorsal-ventrally flattened
• Lateral extension of pectoral fins
• Mostly benthic, feed on invertebrates
• Teeth flat plates that look like paving stones
• Used with powerful suction to dislodge and crush
  invertebrates

3
Skates vs. Rays

• Skates
• Thick, fleshy tail
• 2 dorsal and a caudal fin
• oviparous

• Rays
• Tail whip-like
• Fins on tail replaced by barbs, usually serrated
  and venomous
• viviparous
• Some with sexually dimorphic dentition males
  grow sharp cusps during breeding season to hold
  onto female

4
Sharks

• Ampullae of Lorenzini detect electrical
  potentials and subtle changes in temperature
• Sensitive chemoreception
• Rod-rich retina with guanine crystals behind
  retina tapetum lucidum
• High brainbody mass
• Many (not all) use ram ventilation
• Likely to have social behavior, although
  relatively unstudied

5
Sharks Jaws

• Cranial kinesis mobility within cranium can
  eat huge food items
• Possible b/c of hyostylic jaw (Fig.5-5c)
• Palatoquadrate (upper jaw bone) braced in the
  rear by hyomandibula, which rotates
• Palatoquadrate braced in front by stretchy
  elastin fibers
• Therefore, jaw can protrude upper jaw (see photo)

6
Shark Feeding Behavior(specific to great white
shark, Carcharodon carcharias)

• Use olfaction, electroreception, and vision in
  that order
• Olfaction to smell food over long distances
• Electroreception to locate struggling prey when
  in the vicinity
• Vision to attack
• Nictitating membrane protective eye covering,
  closes during attack electroreception takes over
  for vision when membrane is closed

7
Shark Feeding Behavior(specific to great white
shark, Carcharodon carcharias)

• Seal vs. sea lion
• With seal, shark bites, holds tightly, protrudes
  jaw to tear off a bite
• Lets seal body float to top while eating
• Defends seal body from other sharks via tail
  slaps, tail lobbing, breaching
• With sea lion, shark bites repeatedly, lets sea
  lion bleed to death, then bites off chunks

8
Shark Reproduction

• Males with claspers on pelvic fins
• Skeletal structure likely increases
  effectiveness
• Clasper bends 90 degrees
• Clasper groove on clasper lies under cloacal
  papilla, where sperm are emitted
• Male inserts clasper in females cloaca locked
  there with barbs, spines, etc.
• Sperm ejaculated, funneled by groove
• Seawater from siphon sac wash sperm into female

9
Shark Reproduction

• Oviparous, viviparous, or ovoviviparous
• When eggs are young leave mother, no parental
  care
• When oviparious, nidimental gland secretes
  proteinaceaous case around egg
• Camouflages egg as kelp (Fig. 5-6b)

10
Goings-on in the Shark Uterus

• Intrauterine siblicide eggs ovulated until only
  a few uterine rivals left
• Extensions of oviduct walls penetrate fetal
  mouths and secrete milk
• Yolk-sac placenta highly vascularized, allows
  fetal shark to obtain nourishment from mothers
  blood

11
Shark-Human Interactions

• Many young sharks depend on shallow inshore
  waters, where we like to hang out.
• Over-fishing people like to eat sharks
• fish and chips
• Mako shark steaks
• Sharkfin soup
• more demand b/c of rapid economic progress in Asia

12
Shark-Human Interactions

• Shark finning
• Set out long-line, go along and pull in shark,
  de-fin it, and through body back
• Outlawed in U.S. in 2000, but easy for shark
  finners to go just outside U.S. jurisdiction not
  illegal to sell shark fins
• UN ban on shark finning in 2003, but no
  enforcement

13
Shark-Human Interactions

• Important natural history info for management
• Grow slowly
• Reach sexual maturity late in lives
• Have few young at one time
• Females dont reproduce every year b/c invest a
  lot of energy in offspring (egg production,
  yolk-sac placenta, etc.)
• Top-level predators extinctions have drastic
  effects on ecosystems