Chondrichthyes

1
Chondrichthyes

• Cartilaginous Fishes

2
Defining Characteristic of Chondrichthyes

• Cartilaginous skeleton
• Tough, flexible and lightweight
• Increases efficiency of swimming

3
Class Chondrichthyes

• Split into 2 subclasses
• Elasmobranchisharks and rays
• 800 species
• Very diverse
• Holocephalichimeras
• 30 species
• All very similar

4
Characteristics of Subclass Elasmobranchi

• Multiple gill slits (usually 5-7)

5
Subclass Elasmobranchi

• 3 Superorders
• GaleomorphiGaleomorph sharks
• SqualimorphiSqualomorph sharks
• BatoideaSkates and rays

6
Galeomorph sharks

• Sharky-looking sharks
• Anal fin
• Dominant predators of shallow warm ocean waters

7
Gaelomorph Sharks
ANAL FIN
8
Squalomorph sharks

• Not so sharky-looking
• No anal fin
• Deep-sea sharks
• Dogfish sharks, angel sharks and saw sharks
• Relationships within this group are uncertain

9
ANGEL SHARKS
M Harris
DOGFISH SHARKS
SAW SHARKS
10
Megamouth shark(Megachasma pelagios)

• Filter feeder
• Discovered in 1976
• Has been seen fewer than 20 times

11
Skates, Rays, and Guitarfish

• Bottom-dwelling
• Flat
• Large pectoral fins attached to head
• No anal fin
• Eyes and spiracles on top of head
• Pavement-like teeth for crushing inverts
• Gills on ventral (tummy) side

12
Skate or Ray?

• Skates
• Long, thick tail stalk supporting 2 dorsal fins
  and a caudal fin
• Oviparous

• Rays
• Whip-like tail stalk with a venomous dorsal barb
  instead of fins
• Ovoviviparous

13
Skate or Ray?
H Carvalho
LO Duarte
RAY
SKATE
14
Skate or Ray?
RAY EMBRYO
SKATE EGG CASE MERMAIDS PURSE
15
Guitarfish

• Intermediate between sharks and rays
• Harmless
• Ovoviviparous

16
Subclass Holocephali

• 1 OrderChimaeriformes
• 3 families
• No spiracle
• Only 1 gill opening each side of head (sharks
  and rays have 5-7)
• Tail is symmetrical (sharks and rays are
  asymmetrical)

17
Chimaeras (ratfish)

• Bottom dweller
• Eat crustaceans and molluscs
• Spine in front of dorsal fin with a venom gland
  for defense

18

• Produce only 2 eggs at a time
• Claspers on head and pelvic finsunknown use
• Oviparous

egg cases
19
Obtaining Oxygen

• RAM ventilation
• Must swim or die
• Great white shark, mako shark, great hammerhead
  and others

20
Obtaining Oxygen

• Buccal pumping
• Skates and rays, most species of sharks
• Steady flow of oxygen across gills
• Same as most bony fish

21
Obtaining Oxygen

• SPIRACLES
• An opening behind eyes
• Bring water to gills
• Can sit on the bottom and still breathe
• In some pelagic sharks, these operate
  independently of gill, instead bring oxygen to
  the eye muscles

22
Buoyancy

• No swim bladder
• Many dont need to floatstay on bottom
• Big oily liver
• Tail provides lift in sharks

23
(No Transcript)
24
Heterocercal tail helps stay near the bottom
while swimming
More homocercal tail helps provide thrust for
swimming fast
25
Sensory SystemsVision

• Rely less on vision than other fish used at
  close range
• Can see color
• See well during the day and in low light

26
Nictitating membranes cover eyes when about to
seize prey
27
Sensory systemselectroreception, smell and
hearing

• How sharks locate prey
• Smell
• Reception of electrical currents emitted from
  muscle contractions of prey
• Vision

28
Sensory Systemstaste

• Sharks will spit out the Moses sole
• Secretes toxic substance from bases of dorsal and
  anal fin rays
• Substance could be used as shark repellent?

29
Thermoregulation

• Some sharks (family Lamnidae) can generate heat

30
Scales

• All have placoid scales
• Sharks have tiny, overlapping scales that feel
  like sandpaper
• Increase hydrodynamic efficiency
• In some fast-swimming sharks, channels between
  scales to decrease turbulence
• Some slow-moving sharks have stouter scales for
  defense

31
PLACOID SCALES
32
Scales

• Placoid scales modified into
• Barb of stingray
• Dorsal spines of dogfish sharks
• Defensive spines on skates
• Teeth of sharks and rays

33
BARB OF STINGRAY
DEFENSIVE SPINE
34
Teeth

• Rows of teeth are shed and replaced
• Can lose up to 30,000 teeth in a lifetime
• Each shark and ray species has distinctive teeth
  that reflect how it makes a living

35
(No Transcript)
36
DietLarge fish and mammals

• Predatory sharks
• Serrated teeth for tearing off chunks of big prey

37
Dietsmall fish

• Teeth that come to long thin points
• Can hold onto prey until it can be swallowed

38
DietSmall fish and invertebrates

• Rows of small sharp teeth
• Filter feeders like whale shark

39
DietInvertebrates

• Flat, pavement-like teeth
• Crush hard-shelled invertebrates (like clams)
• Skates and rays,

40
How a shark bites

• Large bladelike teeth for grabbing and sawing or
  snapping off large chunks
• Jaws have pressure up to 2800 kg/cm3
• Jaws loosely attached to head
• Lower jaw moves first, then upper
• Cant move jaws back and forth so must shake head
  back and forth

41
Reproductive Strategy
K

• K-selected
• Long-lived, slow to sexual maturity
• Long gestation periods (6-22 months)
• Produce a small number of large, active young
• Offspring have a good chance of survival

42
Sharks are Sexually Dimorphic
MALE
FEMALE
43
Females have thicker skin, to withstand bites
from males while mating
44
John Stevens
45
Oviparity (egg-laying)

• All skates and chimaeras, many sharks
• Large eggs covered with tough leathery cases and
  tendrils at corners
• May take up to 15 months to hatch
• Female horn sharks carry eggs and nudge into
  crevices

46
Ovoviviparity

• Produce thin-shelled eggs
• Eggs are retained in female uterus
• Shell disappears and young stay in uterus until
  fully developed
• Obtain nutrition from a yolk sac
• Rays and some sharks

47
YOLK SAC
48
Viviparity (live bearing)

• Some sharks
• Eggs retained in uterus
• Mother secretes a nutrient-rich fluid
• Young ingest or take up fluid through skin
• Membrane covers embryos teeth

Eve Bunting
49
Cannibal Viviparity

• Some sharks
• Eggs retained in uterus
• Hatchlings have teeth
• Those that hatch first eat the other embryos
• Mother continues to produce eggs for them to eat

50
Young

• Females move into shallow protected area to give
  birth
• Females do not eat during birthing period
• 2-60 pups per litter
• Young are miniature adults
• Quickly disperse and hide
• No parental care

51
Shark Attacks

• Most US attacks occur in Florida
• 75-11 bites each year
• lt20 are fatal
• You are more likely to be killed by a pig than a
  shark!

52
Why do sharks attack humans?

• Interpret swimmers behavior as threatening
• Think small submersible vehicles are predators
• Male whale sharks think large boats are
  competitors and will ram them
• Prefer prey with high fat content, will spit out
  skinny humans

53
Man-eaters

• Of 350 species, 32 have attacked humans,
  especially
• White shark (Carcharodon carcharias)
• Oceanic whitetip shark (Carcharinus longimanus)
• Bull shark (Carcharinus leucas)
• Tiger shark (Galeocerdo cuvieri)
• BUT almost any shark will attack if provoked

54
Conservation Issues
Shark fin soup
55
Conservation Issues

• Shark Cartilage Pills
• No evidence ingesting it combats cancer
• More than 200,000 sharks killed every month to
  make these products

http//healthwatcher.net/Quackerywatch/Shark-carti
lage/
56
Conservation Issues

• Why no shark-safe tuna?
• Sharks also caught in nets along with dolphins

57
Conservation Issues

• Sport Fishing
• Some species are not sexually mature until age 30
• Takes a long time for a population to bounce back
  if over-fished

58
Conservation Issues

• Harassment?
• Adventure sports

59
(No Transcript)