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Chondrichthyes

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Title: 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
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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
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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
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