Week 13 Flashcards
1
Q
There are more species of _____ than all other vertebrates combined.
A
Blank 1: fish or fishes
2
Q
Select all that apply
Choose all features of the first fishes.
They were short (less than 1ft long). They had well formed paired fins. They used gills for respiration. They did not have a tail. They had a head.
A
They were short (less than 1ft long).
They used gills for respiration.
They had a head.
3
Q
Jawed fishes first appeared in the fossil record during the ______
period, roughly 438-408 million years ago.
A
Silurian.
4
Q
Select all that apply
Which of the following are key (defining) features of jawed fishes?
A
- paired appendages
- internal gills
- a vertebral column
- nutritional deficiencies
- single-loop circulation
5
Q
A fish heart contains how many chambers?
A
2
6
Q
Which of the following groups has the most species of vertebrates?
A
fishes
7
Q
Identify the three amino acids that fish are unable to synthesize.
A
phenylalanine, tryptophan, and tyrosine
8
Q
Which of the following accurately describes the first fishes?
A
They had a head and a primitive tail. Most had no vertebrae, although some had rudimentary vertebrae.
9
Q
Which of the following describes lampreys?
A
jawless
no paired appendages
breed in freshwater
10
Q
Which of the following is not one of the five key features of fish?
A
internal organs
11
Q
Select all that apply
Identify all of the structures found in ostraderms.
A
Internal cartilaginous skeletons
Bony head-shields
Flat head
12
Q
Identify the type of blood circulation that is found in fish.
A
Single-loop
13
Q
Phenylalanine, tryptophan, and tyrosine belong to the _____ amino acids.
A
aromatic
14
Q
evolved from the anterior gill arches of ancient, jawless fish.
A
Jaws
15
Q
Choose all features of the first fishes.
A
They were short (less than 1ft long).
They used gills for respiration.
They had a head.
16
Q
Armored fishes and spiny fishes had internal skeletons made up of
A
cartilage
17
Q
Which of the following characteristics apply to hagfishes?
A
No paired appendages Jawless Well-developed sense of smell Tooth plates rather than jaws knotting behaviour Anterior sensory tentacles
18
Q
Ostraderms thrived during these periods of history: _____ and _____ .
A
Ordovician
Silurian
19
Q
_____ developed on the jaws of fish from the modified _______ on the skin that lined the mouth.
A
Teeth
Scales
20
Q
Which of the following are placoderms?
A
Armored fishes
21
Q
How do hagfish reproduce?
A
Dioecious- separate males and females
22
Q
What is the defence system of hagfish?
A
slime
23
Q
What are characteristics of lampreys?
A
Anadromous/semelparity
Ammocoete larvae
use buccal funnel to attach to other fish
Inefficient tidal gill system when eating
definitely dioecious
24
Q
How did the jaw evolve?
A
Serial theory: evolution of jaws from branchial arches
25
What are the Gnathostomes?
Jawed vertebrates-
3 extant classes
2 extinct classes (acanthodians and placoderms)
26
What are the Choondrichyes?
One of the extant gnathostome classes
Made of the subclasses holocephali (ratfishes) and the elasmobranchs (sharks, skates and rays).
Cartilaginous skeleton
Placoid scales (aka dermal denticles- similar in structure to teeth)
Serial tooth eruption
Buoyancy through use of heterocercal tail,fins and low density oils
Adaptations for osmoregulation
Reproductively diverse
Passive electroreception
27
Chordates are ______ animals that belong to the clade of animals known as ________.
bilaterian
| Deuterostomia.
28
What is the fourth biggest animal phyla?
Chordates
They are the fourth biggest animal phyla, a lot bigger than the lophophorates. However, the chordate phylum is much smaller than the arthropods, nematodes and the molluscs.
29
What are the defining features of the chordates?
their apomorphies
notochord, dorsal hollow nerve cord, pharyngeal gill slits and the muscular post-anal tail. Sometimes you see the muscular post-anal tail missed off. It is these four apomorphies that we use to define what a chordate is.
30
What are apomorphies?
which is a novel evolutionary trait that is unique to a particular group.
31
What is a notocord?
- -Is a longitudinal, flexible rod- so it goes along the length of the chordate body and it lies between the digestive tube and the nerve cord.
- --Provides skeletal support throughout the length of the chordate.
- --Some vertebrates have remnants of this notochord, as its been replaced over time by more complicated jointed skeletal elements called vertebrates. In most vertebrates, a more complex, jointed skeleton develops, and the adult retains only remnants of the embryonic notochord.
32
What is a dorsal hollow nerve cord?
- --Its hollow because it’s developed from a plate of ectoderm that rolls into a tube.
- --Its dorsal because it lies on the dorsal side of the body, so this top side and its dorsal to the notocord as well.
- --Develops into a central nervous system, which includes the brain and the spinal cord.
33
What is the Pharyngeal slits or clefts?
- --In most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body.
- --They can be used for suspension feeding in invertebrate chordates and they can also be used for gas exchange in the vertebrates.
- --But this is excluding the vertebrates with limbs.
34
What is the Muscular, Post-Anal Tail?
- --Chordates have a tail posterior to the anus.
- --In many species, this tail is greatly reduced during embryonic development, just like our own tail. Human embryos do have a tail but they lose it by week nine of development.
- --The tail contains skeletal elements and muscle.
- --It provides a propelling force in many aquatic species.
35
What are the Cephalochordates?
Fish like but they’re not actual fish. And they spend most of their time buried in the sediment with their head poking out. Four apomorphies are present here. Find them mostly in rivers and estuaries.
36
What is the difference between the apomorphies of larval and the adult form of the Cephalochordates?
The four apomorphies are also present clearly on the right hand side of the larval form. In the adult form some of these important features are lost. It only retains these pharyngeal gill slits.
37
What are the aspects of the urochordates and cephalochordates?
-Two groups of invertebrate deuterostomes, are more closely related to vertebrates than to other invertebrates. Even though this is true they have some major differences to the vertebrates.
BUT they:
Use their pharyngeal slits for filter feeding, not for respiration
Lack a head
Lack vertebrae
38
What are the three main steps to becoming a vertrebrate?
There are three main stages involved in getting from an invertebrate to a vertebrate.
1. The muscularization of the pharynx
2. Cephalisation is the development of a head
3. Vertebrae
39
What does the muscularization of the pharynx involve?
* This involves the evolution of a band of muscles around the pharynx
* And the development of elastic cartilage which supports the transformed pharynx into a pump
* When the muscles contract, the water is expelled through the gill slits into the outside environment
* When the muscles are relaxed, water is drawn into the mouth of an organism
* There is an evolution from the cilia on the pharyngeal slits into an active pump
40
What does Cephalisation is the development of a head involve?
* The head is a concentration of sense organs at the anterior end of the animal
* And the enlargement of the central nervous system in this region to form a brain
* This is normally covered by a skull
41
What does the vertebrae step involve?
* The backbone
| * Defines the axis of the body of the vertebrate.
42
How do we divide all of the deuterostomes?
Can divide all of the deuterostomes up by capitalization. Those with a head and those without a head.
43
What are the aspects of the ancestral deuterostome?
* Branches and splits into two
* The first group is the echinoderms
* The second group is the chordates
* All chordates apart from the cephalochordates and the urochordates have a head
* The chordates are split between those that do not have a head, and those that do have a head – which are the craniates
* The head evolved from an ancestor that was like a cephalochordate – we have some understanding of this from molecular biology
44
How did the head evolve?
Nerve cord of a lancelet embryo
Central nervous system of a vertebrate embryo
In both cases, we find the same pattern of Hox genes
•Hox genes are a group of related genes that specify body plan along the anterior-posterior axes of metazoans
•They are expressed during the development of an animal
•The Hox3, BF1 and Otx genes are all similarly expressed here
The brain of a vertebrate, which is split into the forebrain, the midbrain and the hindbrain is simply an elaboration of the structure found at the rostral, or anterior end, of the lancelet dorsal nerve cord.
•The vertebrate brain is an elaboration of the ancestral structure
•The vertebral brain is homologous with the rostral tip of the dorsal nerve cord of lancelets
The evolution of a head opened up a new way of feeding for chordates – they could now become active predators
45
What are Hox genes?
group of related genes that specify the anterior-posterior axes of metazoans.
46
What may be suggested about the evolution of the head?
This suggest that the vertebrate brain is an elaboration of an ancestral structure, i.e. the vertebrate brain is homologous with the rostral tip of the dorsal nerve cord of lancelets
47
The evolution of the ______ is well documented in the fossil record from the ______ ______ which was about ___ Million years ago
craniates
Cambrian explosion
530
48
What is one of the well known fossils?
•There are several well known fossils
•One of them is Haikouella
•It was about 3 cm long
•It had a well formed brain, eyes, and muscular segments
•It had no vertebrae and no skull
Although it was a chordate and a craniate, it was not a vertebrate
49
What are the hagfish?
The hagfish are craniates but are not vertebrates
•So they are a sister group to the vertebrates
•Sister groups are monophyletic groups that are each other's closest relatives.
50
What is the vertebrae?
are separate blocks of cartilage or bone
51
What does the vertebrae form?
•They form the backbone that defines the main axis of the body
52
What does the typical vertebrae have?
has a centrum
53
What is a centrum?
This is a cylinder enclosing the notochord
54
What does the intervertebral disc or body do?
The intervertebral disc or body divides the sections that separate each vertebrae from the next
55
In mammals what is the intervertebral disc?
In mammals, the intervertebral disc is a jelly-like remnant of the notochord
56
There is a dorsal neural arch which houses
the dorsal nerve cord
57
There is a ventral hemal arch which houses
the axial blood vessels
58
These arches often form
spines for the muscles to attach onto this structure
59
Definitions of “Fishes”
* A Paraphyletic Group: “Craniates that are not Tetrapods”.
* “Aquatic vertebrates that have gills throughout their lives, and limbs, if any, in the form of fins”
There are around 49,000 species of vertebrates, and about 25,000 species are fish- make up half of vertebrates
•The number is increasing as more species are discovered, but is expected to plateau at around 29,000 species
This large number is mainly due to their radiation out of the shallow ancestral waters into just about every marine and freshwater habitat on earth.
60
Where do fish inhabit?
Fish are found in extreme locations
•Hot springs in Tibet 5000 meters above sea level
•5000 meters below sea level in the deep oceans
•They can live in very cold and very hot temperatures, in the Antarctic where the water is minus 2 degrees Celsius
•They can also be found in hot soda lakes in Africa which can reach temperatures of 44 degrees Celsius
This shows you how diverse the fish have become. They can live in all these extreme habitats.
61
What are the morphological differences of fish?
Adults can range from very small – this goby fish is only 8mm long
•Up to very large, such as this whale shark which is 12 m long, which is the worlds largest fish
Their body form can vary greatly
•They can be string-like and streamlined
•Or a ball shaped
•This all depends on the ecological niche that they occupy
62
What is the Cyclothone?
* It is a genus of small deep sea fish
* They are about 50 mm long
* Their common name is the bristlemouth
* They are probably the worlds most abundant vertebrate genus in terms of numbers of individuals
* This animal could be described as a typical vertebrate
63
What are the Derived Characteristics of Vertebrates?
* Vertebrae enclosing a spinal cord
* An elaborate skull
* Fin rays, in the aquatic forms
64
•Vertebrates evolved in the _________ and probably succeeded because they became more efficient at ______ and _______.
Cambrian period (541 – 485 million years ago)
catching food
avoiding predators
65
What are the three features that define Cyclothone?
* They have vertebrae which enclose a spinal cord
* They have an elaborate skull
* They have fin rays in the aquatic forms
•Don’t see these in the tetrapods like us, where have evolved these different limbs.
66
What are Lampreys?
* Lampreys (Petromyzontida) represent the oldest living lineage of vertebrates
* Jawless fish (AGNATHANS)
* Once grouped with hagfishes as ‘Cyclostomes’ (‘Round mouths’)
* Lampreys represent the oldest living vertebrates
* They were once grouped with the hagfishes as Cyclostomes – which means round mouth but they have since been taken out of this and are included within the vertebrates.
67
What surrounds the notochord in lampreys?
• Cartilaginous segments surrounding the notochord
These are definitely vertebrates and are probably more closely related to other vertebrates, including those with jaws, than they are to hagfish.
•They have cartilaginous segments surrounding the notochord and arching partly over the nerve cord
68
What are features of both the hagfish and the lampreys?
•Both the lampreys and the hagfishes are jawless fishes in the superclass Agnatha
69
What are Sea lamprey Petromyszon marinus?
* They have no paired fins
* They have dorsal and caudal fins – no side fins.
* Most live in freshwater
* But some of them, like the sea lamprey can live in saltwater for part or all of its lifecycle
* The term for fishes that spend some of their life in freshwater and some in saltwater is diadromus
* The lampreys spend most of their time in seawater, and then they come to breed in freshwater
* This is called an anadromous lifecycle
* (A catadromous lifecycle is where the adults live in freshwater but travel to sea water to breed)
* They only breed once in their lifetime
* This is semelparity – or ‘big bang’ reproduction
70
Diadromous
Lives in sea water and freshwater in life cycle.
71
Anadromous
=breeds in freshwater
72
Catadromous
breeds in sea water
73
Semelparity
Big Bang Reproduction- breed once in life.
74
What is involved in spawning adults?
* Eggs are laid in nests of stones and are fertilized externally
* Then the adults die
* The larvae look very different from the adults
* They were once named as a separated species called the ammocoetes so they are now called the ammocoetes larvae
* The larvae are about 5 – 10 mm long
* They are pink and worm-like
* They live for about 5 years in the sediment or mud and they emerge at night to feed
* They feed on organic detritus which they suck into their funnel-like mouths
* The food is then strained and passed to their pharynx where it is trapped by sticky secretions made by the endostyle
75
What are the Lamprey Ammocoete larva?
Feed using sticky secretions from Endostyle
1. Apomorphy of the Chordates (i.e. a unique derived feature)
2. Binds Iodine
3. Homologue of Thyroid Gland
76
What is the endostyle?
* A very unique derived feature of the chordates
| * It is found in the invertebrate chordates where it acts as a sticky food trap
77
What does the endostyle bind?
binds iodine – in the mammals this function is preserved in the thyroid gland
•Therefore the thyroid gland is homologous to the endostyle
•In other words the endostyle and the thyroid gland are both derived from the same ancestral structure
78
What do ammocoete larvae also have?
have a simple gill ventilation system
•Water enters the pharynx via the mouth and exits via the gill slits
•Water flow is effected with a muscular pump called the velum as well as with cilia
79
Adult lampreys are
active mobile swimmers
•They are predatory and attack other fish
They emerge from the stream bed as adults
80
How do adult lampreys feed?
•This is the parasitic phase because they feed by attaching on to fish
They are primarily visual feeders
•Unlike the larvae or the hagfish, they have quite large eyes
81
What is a unique feature of the lamprey?
is the buccal funnel
•This is the structure that allows them to live a predatory lifecycle without having a jaw
•It has suckers all around the margin
•It has a mobile tongue in the center
•With teeth that can rasp at the flesh all around the body
82
Today, the jawed vertebrates (called the Gnathostomes) –
outnumber the jawless vertebrates
83
Summarise elements of Hagfish.
```
Tooth plates rather than jaw
Knotting behaviour
Anterior sensory tentacles
Reproduction: Dioecious
Defense: Slime
```
84
Summarise elements of Lampreys
Anadromous / Semelparity
Ammocoete larvae
Use buccal funnel to attach to other fish
Inefficient 'tidal' gill system when eating
85
Summarise elements of the evolution of jaws.
Serial theory: evolution of jaws from branchial arches
86
What are the Gnathostomes?
There are only five classes of Gnathostomes that are recognized
•Three of those are living, or extant
•Two of them are extinct
87
Acanthodii or the spiny sharks-
Even though they are called spiny sharks, they are not related to sharks
They are some of the earliest fishes with jaws
They were common about 350-400 million years ago
They were extinct by 250 million years ago
88
What are some features of the spiny sharks
•Only about 20 cm long
•They had jaws and large eyes which is common in predators for prey detection
•They were mostly pelagic – pelagic zone is between the surface and the sea floor. Have different areas within the pelagic zone, like mesopelagic etc, so its quite a large part of the water column.
They had spines, which had skin flaps attached from the spines to the body
And they had spiny fins – which were not always paired – this was to give them roll stability
They had a heterocercal tail,
The design of the tail can give them thrust for propulsion and it can also produce lift
This is thought to be primitive characteristic
It is thought this tail evolved for a pelagic lifestyle
They ate plankton
As well as participating in active pelagic predation
89
What where the placoderms?
They were around at more or less the same time as the Acanthodians
They were common about 350 million years ago
And they were extinct about 250 million years ago
90
Dorso-ventrally flattened
•This is thought to indicate that they were demersal species – meaning that they live near, on or in association with the ocean floor or the bottom of the water body.
91
The head of the Placoderm
Heavy head shield
Trunk shield- behind the head
These were thought to be hinged so that they could rock up and down, probably to pump water over the gills
•And also to help suck up food
Although they had jaws, they did not have teeth – instead they had tooth plates
The tooth plates were quite complicated – some had sharp cutting edges, other were flat for grinding
This indicates that they exploited a diverse range of prey
92
Chondrichthyes means
cartilaginous fishes
93
Chondrichthyes include
* This includes the skates and the rays
* These are potentially one of the first walking animals walking along the seafloor around 400 million years ago.
It also includes the sharks
•This is a great white shark
The cartilaginous fishes only arose slightly later than the Acanthodians and the Placoderms
•They had a huge radiation between 400 – 300 million years ago
•During this time they would have shared the seas with the Acanthodians and the Placoderms
•Today their numbers are much reduced, there only about 750 species of extant shark, rays and their relatives
94
•The two extinct classes of Gnathostomes are
the Placoderms and the Acanthodians
95
The extant Chondrichthyes, are divided into
two subclasses
| •These are the Holocephalans and the Elasmobranchs
96
•The Elasmobranchs are
the sharks and the rays
•There are 9 orders
•There are more species of rays
97
•The Holocephalans
•Just one order, the Chimaeriformes or chimaerids, also known as the ratfishes
98
What are the Chimera, known as a rabbit fish or rat fish?
They are benthic and they are predators of invertebrates
They live on the continental slope in fairly deep water- so not really seen by humans.
•For this reason they are not often seen and are quite rare
•continental slope- this massive slope that descends into the ocean on the verges of continental plates.
They differ from sharks in many ways, the most obvious being that they don’t have separate gill slits but instead they have an operculum
•In the rat fish this comes in the form of a cartilaginous flap covering the gills
99
General features of the Chondrichthyes include
Cartilaginous skeleton
•Chondrichthyes means cartilaginous fish
•It is not surprising to see that is a common feature
•It is kept all throughout their life and is not replaced by bone
•This may be a derived feature of this group
The second feature present in all of the Chondichthyes are the placoid scales.
100
Buoyancy in Elasmobranchs
Having a “heavy” body is ok if you are a benthic predator!
“heavy” meaning “dense”
Although they have no mineralized bones, Elasmobranchs are relatively heavy bodied
By heavy, we mean dense
This is a positive advantage to benthic predators like rays
Because they live on the sea floor and want to be as close to the sea floor as possible
So floating away would not be good for them
If they want to explore the pelagic niche they need to generate lift to counteract this weight
101
What are the two ways that sharks generate lift?
Dynamic lift requires movement for lift to be created
•When they are swimming the combined effects of the asymmetrical heterocercal tail
•And the hydroplane-like pectoral fins
•Together these create the dynamic lift
Static lift is integral and does not require movement
•This is by using low density oils in their bodies
•Which lowers their overall density
•In Elasmobranchs these oils are stored mainly in the liver
•Squaline is a pale yellow oil which has a relative density of about 0.86
102
Sharks have large
livers
103
What is the function of the liver in sharks?
* In humans the liver accounts for about 5% of our body mass
* In sharks it can be around 25% of their body mass
This is a dissection of a deep sea shark which has been opened up
Without static lift sharks would have to generate much more dynamic lift
•Which means they would generate more drag, swim more slowly and use more energy
•So the liver containing the low density oils is a really important feature for the success of the sharks, they don’t have to use as much energy.
•The intestine is relatively short, but the surface area is increased by these spiral valves which you can see inside here
These spiral valves are also found in the lampreys
And even in some bony fish
•This is a simple way of increasing the surface area of the gut for better absorption of nutrients
104
What is an osmole?
is a unit of measurement which defines the number of moles (a mole is a unit of measurement for the amount of a chemical substance in terms of molecules) of solute that contributes to the osmotic pressure of a solution.
105
Why do Chondrichthyes have a problem?
because they live in sea water
•Sea water has roughly three times the osmolarity of their blood
•I.e. Sea water is a solution that is about three times more concentrated than their blood
•It is about 1000 mOsm/kg compared to the vertebrate blood osmolariy which is 300 mOsm/kg
•The rules of osmosis therefore result in water tending to flow out of the vertebrate blood
•And ions tending to flow down their concentration gradient in to the vertebrate blood
•This is a similar situation to animals living in deserts, where it is very important for organisms to conserve and retain their water
106
How do they make sure they are not losing water to the sea permanently?
To retain water, they accumulate high concentrations of urea in their blood, about as high as about 400 mOsm/kg
This helps a lot (300 from the normal blood osmolarity and 400 from the urea is 700 mOsm/kg) but it is still not quite the same osmolarity as sea water – which is 1000 mOsm/kg
They also accumulate other nitrogenous compounds such as trimethylamine oxide (TMO) and amino acids
This adds up to another 400 mOsm/kg
So the components of the blood together are similar to the osmolarity of the sea water
107
What is the benefit of they accumulating high concentrations of urea in their blood?
* This method is energetically cheap – urea is a waste product
* But it requires the animal to produce special proteins to counteract the protein destabilizing effects of urea - blood concentrations as high as 400 mOsm/kg would kill most other vertebrates
108
How do they get rid of the excess ions that tend to flow in?
Sodium and chloride ions tend to be absorbed because they are at lower concentrations internal to the organism than in the seawater
To solve this they actively pump ions out into the seawater through ion pumps in the gills or rectal glands
109
Pristis- The Sawfish-
A derived ray that has invaded freshwater
•Low blood ion concentrations
•Very low urea conc.
•Degenerate rectal glands
110
Most Chondichthyes are ______, but a few, such as this _____which is called ______, and some ______, have invaded ______.
```
marine
sawfish
Pristis
stingrays
freshwater
```
111
How have the stingrays adapted?
* It is a highy derived ray
* To manage living in freshwater it has evolved three features
* It has low blood ion concentrations
* It has very low urea concentrations
* Its rectal glands have become secondarily degenerate
112
What are the features of the gills of a shark?
The gills primary function is in gas exchange
•The Elasmobrachs have 5-7 gill pouches
•These can open independently
113
Why are shark gills different from the Chimerids (ratfish)?
•This is different from the Chimerids (ratfish) where the gills are covered by an operculum
114
What do the Elasmobranchs have?
* The Elasmobranchs also have a small opening called a spiracle
* This is a vestigial gill slit
115
What are aspects of the Cartilaginous skeleton of the head region of a dogfish?
Well developed cranium
The jaw consists of the hyoid arch and the mandibular arch
•The Gnathostome jaw structure has evolved from the primitive Agnathan branchail arches
The gill slits are separated by branchial arches
•It is not that much of a stretch to think that the jaw formed from one of these branchail arches if there used to be a branchial arch where the hyoid arch is now
•The hyoid arch is formed of two sections, the hyomandibular section and the hyoid bar
•The mandibular arch is formed of two sections also; the palatoquadrate and Meckel’s cartilage
Between the hyoid arch and the mandibular arch, the remnants of the ancient gill slits have been squashed, almost out of existence
•But in the sharks and rays can still be found as this spiracle – a vestigial gill slit
Ventilation of the gills in the Chondrichthyes involves a complicated cycle of movement of the mouth and the branchial cavities
•There is a coordinated opening and closing of the mouth, spiracle and gill slits
This ensures there is an efficient flow of water over the gills for efficient gas exchange
116
Why are mouth movements during feeding difficult?
Mouth movements during feeding are difficult, especially when the mouth is moving as part of the complicated system to enable efficient water flow over the gills
117
What is the function of the jaw during feedign?
The way that the jaws are moved in feeding is quite different
Neither the cartilage of the hyoid arch or mandibular arch are attached to the cranium, so during feeding, both can swing and move
•When the mouth opens to bite, and the lower jaw descends, both the upper jaw and lower jaw swing forward on the hyoid arch
•This results in a ventral and forward jaw shift
•The jaw protrudes from the mouth
•When the mouth is not open for feeding and is at rest, the jaws are retracted back in
A shark in feeding mode – the jaw has swung forward and is protruding from the mouth
118
Not all sharks are
active predators
119
What sharks are not active predators?
* The whale shark is the worlds biggest fish
* It feeds on plankton and has extremely reduced teeth
* Instead of biting other animals, it gulps mouthfuls of water
* It keeps the food in its pharynx near some sieves at the entrance of the gill slits
120
What are the Manta rays (Pelagic rays)?
They manta ray can have a wingspan up to 7m
•They are pelagic rays that have abandoned the benthic existence of most other rays
•They do not lie on the sea floor like most other rays do
•They ‘fly’ through the water column using enlarged pectoral fins
•And they feed on plankton just like the whale shark, so they have reduced teeth
121
Summarise the Gnathostomes
```
3 extant classes
2 extinct (acanthodians and the placoderms)
```
122
Summarise the Chondrichyes (on of the extant gnathostome classes)
Made of the holocephali (ratfishes) and the elasmobranchs (sharks, skates and rays)
Cartilaginous skeleton
Placoid scales (aka dermal denticles - similar in structure to teeth)
Serial tooth erruption
Buoyancy through use of hetercercal tail and low density oils
Adaptations for osmoregulation
Reproductively diverse
Passive electroreception
