Chondrichthyes - the Cartilaginous Fishes Flashcards

1
Q

Class Chondrichthyes

A

“cartilage + fish”
>1300 spp; Devonian speciation (415 mya)
- eg. chimaeras, sharks, skates, rays
- Other than whales, sharks are the largest living vertebrates
Well-developed sense organs
Powerful jaws - predator lifestyle
Powerful swimming musculature
Cartilaginous skeleton
- Heavily calcified (i.e., mineralized tissue) but not true bone
- But phosphatized mineral tissues similar to bone retained in teeth, scales, and spines

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2
Q

What does it mean to have no bones?

A

You can have calcified cartilage without having bone
- Bones are organs: blood flow and cells

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3
Q

Class Chondrichthyes -> Subclass Holocephali

A
  • Only ~ 55 spp.
  • Ratfish, rabbitfish, chimaeras
    (= mythical monster w. parts from many animals)
  • Benthic, deep water
  • Mechano- and electroreceptors on rostrum/snout
  • Fused crushing tooth plates
  • Oviparous (shallow water eggs)
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4
Q

Class Chondrichthyes -> Subclass Elasmobranchii

A
  • “plate + gills”
  • ~1277 living spp. (200 in last decade!)
  • Sharks, skates and rays
  • 5-7 pairs gill slits, usually w. spiracle behind each eye
    • water passage for gills
  • Streamlined fusiform body w. large rostrum (sharks)
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5
Q

Locomotion

A
  • Torpedo-shaped (sharks)
  • Thrust and lift provided by an asymmetrical heterocercal tail
    • vertebral column turns upward and extends into dorsal lobe of caudal fin
  • Paired pectoral and pelvic fins
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6
Q

Organ Systems

A
  • Have all major organs
  • Spiral valve in (short) intestine
    - slows passage of food and
    increases absorptive area
  • No swim bladder (sink or swim)
    -> large fatty liver
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7
Q

Sensory Organ Systems

A

Predation!
- Keen sense of smell -> “swimming noses!” (i.e., blood)
- Neuromasts
- Sensitive to vibrations/sounds
- lateral line system
(mechanical)
- Ampullae of Lorenzini
- detect bioelectric fields of
animals
- Good vision, especially in low light

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8
Q

Jaw Modifications

A

Jaw protrusion in feeding sharks
- Hydrostylic jaw suspension
- Lower jaw + upper jaw attached to chondrocranium via hyoid arch
- Swings forward and out

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9
Q

Scales and Teeth

A
  • Placoid scales: (three prong, face backward), dentine + enamel
  • Dermal origin
  • Modified anteriorly for form replaceable rows of teeth
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10
Q

Reproduction

A
  • Fertilization is internal
  • Pelvic claspers
    • Modifications to male pelvic
      fins for copulations
      Maternal care variable
  • Oviparous (egg hatch)
  • Viviparous (nourished by placenta; live birth)
  • Ovoviviparous (AKA aplacental viviparity– nourished by egg; live birth)
    No care after young are born
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11
Q

Sibling Conflict..

A

Sand tiger sharks
- embryos cannibalize siblings
up to 12 embryos but only 1-2 live births

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12
Q

Galeoid Sharks

A

~370 spp
- Shallow warm water, pelagic
- Streamlined, muscular, fast
- High metabolism, high food (large carnivores)
- Great whites, hammerheads

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13
Q

Squaloid Sharks

A

~200 spp
- deep, cold water
- Long, eel-like, (usually) smaller than Galoids; slow swimming
- No anal fin
- Low metabolism, low productivity, low food

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14
Q

Batoids: Skates and Rays

A

~700 spp (> 1/2 of all elasmobranchs; more diverse than sharks!)
- Dorso-ventrally flattened
- dorsal eyes and spiracles
- Ventral gills
- Ventral protrusible mouth and
crushing teeth
- Benthic, some FW
- Large pectoral fins
- Some can stun (electric currents) or with venemous barb/sting

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15
Q

Skates vs Rays

A

Skates:
- most w. thick tail and 2 dorsal fins that lack spines; oviparous; small teeth
Rays:
- Most w. long whip-like tail; dorsal fins absent/reduced; w. venomous barbs/sting; viviparous, plate teeth

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