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Vertebrate Zoology > Class Chondrichthyes and Sharks > Flashcards

Class Chondrichthyes and Sharks Flashcards

1
Q

What are the defining features of a shark?

A
  • prismatic endoskeletal calcification
  • pelvic claspers
  • placoid scales
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2
Q

Define synapomorphy

A

cladistic term for a defining character of a clade

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3
Q

Describe Chondrichthyes

A
  • bone absent from cartilaginous endoskeleton
  • prismatic calcification of surface layers of cartilage matrix
  • bone in teeth and scales
  • bone abscence lightens body and increases manoeuvrability
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4
Q

Describe Shark Vertebrae

A
  • simple morphology
  • spinal cord in neural canal formed by neural arches
  • notochord sheathed by centrum
  • solid casing of cartilaginous vertebrae
  • neural arches enclose neural canal
  • spinal cord dorsal to notochord in neural canal
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5
Q

Describe the exoskeleton of dogfish

A

early exoskeleton of dermal bone:
* bone forms in skin
* feels rough to the touch due to small placoid scales / dermal denticles

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6
Q

Describe placoid scales

A
  • form in dermis
  • project through epidermis to surface
  • tooth-like structure: enamel tip, dentin, pulp cavity
  • (homologous in structure to teeth)
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7
Q

Describe tooth whorls

A
  • ligamentous band along jaw cartilage beneath flesh
  • developing teeth in file behind each functional tooth - conveyor belt system
  • tooth replacement ~ weekly in young sharks
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8
Q

What does it mean when sharks have cranial kinesis?

A
  • ability to move skulls
  • can protrude upper jaw to get better grip on prey
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9
Q

Define hyostylic jaw suspension

A

jaw not fused to cranium - linked by cartilaginous hyomandibular brances

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10
Q

What allows the protrusion of the upper jaw in cranial kinesies?

A

elastic ligaments

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11
Q

Describe gill openings in sharks

A

separate and uncovered
except chimaeras - soft tissue covering

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12
Q

What are the 2 main ventilation strategies in sharks?

A

ram ventilation
buccal pump

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13
Q

describe ram ventilation

A
  • when shark is moving: water -> mouth -> gills
  • 5 gill pairs
  • constant forward movement to ventilate
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14
Q

What is Pelagic ram ventilation?

A

sharks in deep open ocean won’t rest on seafloor

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15
Q

Which species have obligate ram ventilation?

A

great white, mako, whale sharks

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16
Q

describe buccal pump ventilation

A
  • when shark at rest: water in via mouth and spiracles, out via gills
  • flap valves - no water in via gills
  • ## can rest on seabed (benthic)
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17
Q

which species are obligate buccal pumps?

A

angel, carpet, nurse sharks

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18
Q

How do most sharks ventilate?

A

mix of buccal pump and ram ventilation

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19
Q

Describe the gill structures

A
  • filaments protrude off gill flaps
  • interbranchial septum between gills to allow blood vessels to pass through
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20
Q

Describe filter feeders and a common example

A

Cetorhinus maximus - basking sharks
- gill filament protrudes
- comb-like gill rakers around 10cm
- cartilaginous structures stop material reaching gills
- basking filter zoo-plankton prey

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21
Q

What is the new 2016 theory on filter feeding gills?

A

Sanderson et al
- vortical cross-step filtration
- gill arches create vortices
- vortical flow interacts with gill rakers to concentrate particles along slot margins

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22
Q

What are the 3 filter feeding sharks?

A
  • basking sharks
  • whale sharks
  • megamouth sharks
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23
Q

What are the 2 forms of tribasal pectoral and pelvic fin evolutions?

A

cladoselache (upper devonian)
hybodus (early triassic to late Cretaceous)

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24
Q

Describe cladoselache fins

A

traingular basal cartilage
parallel radial cartilages to margin

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25
Q

describe Hybodus fins

A

stalk of 3 basal cartilages
segmented, shorter cartilages in blade

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26
Q

describe tribasal and pelvic fins in modern sharks

A
  • tribasal structure has mobility and flexibility
  • collagenous fibres ‘ceratotricia’ extend to fin margin
  • muscles within fin
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27
Q

What is the function of pectoral fins?

A
  • horizontal swimming - no lift from pectoral fins
  • to rise: posterior plane of pectoral fins flip up to generate lift
  • to sink: posterior plane of pectoral fins flip down
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28
Q

Describe pectoral wings in skates and rays

A
  • dorsoventral flattening of body
  • wave-like motion to move, large amplitude
  • lateral extension of pectoral fins
  • outer half of wing oscillated most
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29
Q

Describe the caudal fin in the modern shark

A
  • heterocercal -> generates lift
  • dorsal tail lobe > ventral lobe
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30
Q

Describe the caudal fin in Squalus acanthias

A
  • musculature extends into dorsal lobe of dorsal fin
  • sharks swim using wave-like body undulations
  • muscles act as caudal fin - changes shape
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31
Q

Describe shark anal fins

A
  • median fin
  • not present in all sharks
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32
Q

Give an example of a shark with an anal fin, and a shark without

A

with: Mesozoic Hybodus
without: Devonian Cladoselache

33
Q

Describe Median fins

A
  • like dorsal and anal fins balance roll & yaw in locomotion
  • may generate additional thrust
34
Q

Describe the underslung mouth

A
  • evolution of rostral process (snout) due to concentration of packed sensory organs in snout
  • Hybodus did not have - separates from modern sharks
35
Q

What are the hunting senses?

A
  • vision
  • olfaction
  • hearing
  • electroreception
36
Q

Describe vision for hunting in sharks

A
  • spherical lens focused by change in position not change in shape
  • retina rods and cones vary in proportion with habitat
  • reflactive tapetum lucidum behind retina to increase sensitivity
37
Q

Describe olfaction in hunting in sharks

A
  • can smell 1 ppm blood
  • nostrils divided externally by flap of skin: water flows in incurrent nostrils and out excurrent nostrils
  • detects conc. differents between nostrils, turns towards higher conc.
38
Q

Describe olfaction in hammerhead sharks

A
  • elongated but flattened olfactory chambers
  • folded sensory epithelia lining
39
Q

Describe hearing in sharks

A
  • low frequencies of struggling prey attract sharks
  • fish & water same density therefore only inner ear - no eardrum
  • 3 orthogonal D-shaped canals and 2 vestibular sacs
40
Q

What are the 3 orthogonal D-shaped canals in sharks ears?

A

Posterior, horizontal and anterior canals

41
Q

What are the 2 vestibular sacs in sharks ears?

A

utriculus
sacculus

42
Q

How is displacement sensed in the inner ear?

A
  • calcium carbonate otolith and neuromast hair cell clusters
  • deflection of hair cell: in one direction decreased nerve-cell discharge rates, in opposite increase discharge rates
43
Q

How is sound and movement detected in shark hearing?

A

low frequencies only detected, by particle motion

44
Q

Describe the lateral line in shark hearing

A
  • neuromasts also in canals below skin
  • detects water displacement through pores
  • neuromasts wafted directly through water
  • most visible in chimaeras
45
Q

Describe electroreception in sharks

A
  • primary mode of prey detection - rostral process
  • sense weak electric fields generated by other animals - esp blood
  • terminal metre of attack
  • known as Ampullae of Lorenzini
46
Q

Describe the Ampullae of Lorenzini

A
  • pores on head of shark have canals leading to jelly filled sacs
  • canals allow voltage at pore surface to extend to ampulla
  • high resistance walls filled with conductive jelly
  • modified hair cells respond to electric potential
47
Q

Describe electoreception in embyronic sharks

A
  • ‘Bamboo shark’ embryos in egg cases detect electric fields
  • cease respiratory gill movements to avoid detection
48
Q

Describe the coelomic cavity

A
  • contains internal organs
  • subdivided by transverse septum
  • lined by tissue sheets pericardium and peritoneum
49
Q

What is in the anterior pericardial cavity?

A

heart

50
Q

What is in the posterior peritoneal cavity?

A
  • oily liver
  • underneath liver is u-shaped stomach
  • spiral valve
  • excretory organs
51
Q

Describe the single circulation system in sharks

A
  • blood passes through heart once in each circuit
  • heart chambers in series
  • ventral aorta: from ventricle to gills
  • dorsal aorta: from gills to body
52
Q

Describe aortic arches from the ventral aorta?

A

afferent arteries to the gills

53
Q

Where do efferent arteries lead to?

A

from the gills to dorsal aorta and carotid artery

54
Q

Describe the oily liver

A
  • most of body cavity
  • up to 25% body weight
  • buoyancy organ
  • fatty reserves - energy store
  • oil utilised for humans
55
Q

How does the liver act as buoyancy organ?

A

the oils are lighter than water

56
Q

Why do sharks not have bone marrow?

A

blood cells produced in spleen and epigonal organ

57
Q

Describe the excretory organs

A
  • ribbon-like kidneys each side of dorsal midline along length of body cavity
  • rectal gland associated with rectum
58
Q

Describe osmoregulation in sharks

A
  • osmoconformers
  • slightly hyperosmotic
  • reabsorption of urea by kidney tubules
  • urea denatures proteins but countered by accumulation of TMAO
  • rectal gland excretes excess Na+ and Cl - lower salt conc than seawater
59
Q

What are osmoconformers?

A
  • internal osmolarity is close to seawater
  • use urea not salt to keep osmolarity high
60
Q

Why are sharks slightly hyperosmotic?

A

water influx via gills due to use of urea

61
Q

Describe the urogenital system in sharks

A
  • excretory and reproductive systems from similar embryonic tissues
  • some common ducts
  • cloaca
62
Q

What is a common duct in sharks?

A

archinephric duct - ancestral kidney drainage
also for sperm in jawed vertebrates
evolved into part of urogenital system

63
Q

Describe the cloaca

A
  • posterior orifice
  • common opening for digestive, urinary and reproductive tracts
  • in sharks, lobe-finned fish, amphibians, birds, reptiles
  • chamber with 3 compartments separated by folds in wall
64
Q

What are the 3 comparements of the cloaca?

A
  • faeces from intestine
  • urine from kidneys
  • sperm from male sex organs
65
Q

Describe the male shark genital system

A
  • testes - paired structures at anterior dorsal end of coelom
  • spermatozoa mature in epidydimis ducts
  • sperm stored in seminal vesicles for several weeks before mating
66
Q

Describe the female shark genital system

A
  • ovaries - only 1 in dogfish
  • 2 oviducts consisting of: funnel, shell gland, isthumus, uterus
67
Q

Describe claspers

A
  • earliest copulatory organs
  • inserted into female cloaca
  • elongated portions of male pelvic fins - so 2 claspers
  • clasper tip spreads to lock within female urogenital system
68
Q

Describe copulation in sharks

A
  • small flexible sharks - male coils around female
  • large stiff bodied sharks - male lies parallel to female
  • biting of female by male often observed
69
Q

Describe copulation in Paleozoic sharklife forms

A
  • Carboniferous 318 mya
  • fossil claspers
  • appendage on head of male - held by female in possible fossil copulation
70
Q

Describe oviparity in sharks

A
  • shell gland enlarges post-fertilization
  • secretes albumen & collagenous fibrils as eggs pass through
  • eggs - relatively short time in uterus, laid on substate or bottom structures
  • varied egg shapes
  • placental viviparity in half of carcharhiniforms order
71
Q

What is viviparity?

A

giving birth to live young

72
Q

What is an example of egg shape?

A
  • ## spiral to wrap around seaweed
73
Q

Which species tend to lay eggs?

A
  • smaller, benthic and reef forms
  • Catsharks - Scyliohinidae
  • Bullhead sharks - Heterodontidae
  • Wobbegongs - Orectolobidae
74
Q

What are some examples of species that display viviparity?

A
  • deeper water sharks
  • Hammerhead - Sphyrnidae
  • Weasel - Hemigaleidae
75
Q

What are the 3 sections of ovoviviparity?

A
  • lecithotrophy
  • histotrophy
  • oophagy
76
Q

Describe lecithotrophy

A
  • embryos retained in uterus but soley depend on yolk deposited at ovulation
  • 2 orders of rays and squalomorphii shark superorder
77
Q

Describe histotrophy

A
  • more specialised - 1 order, stingray
  • embryo obtains protein and lipid rich secretions from trophonemate in uterus
78
Q

Describe oophagy

A
  • embryo consumes later ovulated eggs
  • precocious dentition
  • mackeral shark order - includes great whites

Vertebrate Zoology (25 decks)

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