Week 9 Flashcards
1
Q
In arthropods, the hard __________
provides protection and physical support, the jointed __________ provide flexibility, and the _________
body plan allows specialization of different body parts.
A
Blank 1: exoskeleton
Blank 2: appendages or legs
Blank 3: segmented
2
Q
Segmented organisms with jointed legs and a hard exoskeleton composed of chitin belong to the phylum ______.
A
Blank 1: Arthropoda or Arthropods
3
Q
Which of the following are advantages of an exoskeleton?
A
protection from predators
support for the body
protection against water loss
4
Q
What is a major disadvantage of an exoskeleton?
A
Restricted mobility
5
Q
Many arthropods possess tagmata. What are they?
A
Body segments that have become fused into functional units
6
Q
Match each arthropod characteristic with the property it confers.
1) Exoskeleton
2) Segmentation
3) Jointed appendages
A
1) Protection and physical support
2) Specialization of body parts for different functions
3) Flexibility
7
Q
In arthropods such as insects, the body is organized into which of the following functional groups or tagmata?
A
Abdomen
Thorax
Head
8
Q
All members of the phylum Arthropoda have what characteristics?
A
Segmentation
Jointed legs
An exoskeleton composed of chitin and protein
9
Q
The exoskeleton of an arthropod is made of protein and a polysaccharide called ______.
A
chitin
10
Q
One of the advantages of an exoskeleton is that it provides
A
support for the body
11
Q
Which of the following accurately describe chitin?
A
It is strong but also flexible in response to the contraction of muscles attached to it
12
Q
A hard exoskeleton provides protection against predators; however, it also restricts an animal’s______.
A
Blank 1: mobility, motion, locomotion, movement, or growth
13
Q
In many arthropods, the body segments have become fused into functional units called
A
tagmata
14
Q
All of the following are functions of the arthropod exoskeleton EXCEPT
A
radiation resistance
15
Q
What are the characteristics of echinoderms?
A
Endoskeleton made of calcium carbonate plates
Adults have pentaradial symmetry
Deuterostome development
16
Q
What substances make up the exoskeleton of an arthropod?
A
Chitin and protein
17
Q
Which of the following refers to an organism whose body has five axes of symmetry?
A
Pentaradially symmetrical
18
Q
Arthropod exoskeletons are composed of chitin, which is similar to cellulose in that it is both ______
and _______.
.
A
Blank 1: strong or tough
Blank 2: flexible
19
Q
Which of the following is true of both of the nonvertebrate chordates Urochordata and Cephalochordata?
A
They have a notochord.
20
Q
Organisms with spiny skin that exhibit pentaradial symmetry as adults, and have an endoskeleton made of calcium carbonate plates, make up what phylum?
A
Echinoderms
Echinodermata
21
Q
An organism whose body has five axes of symmetry is _____
symmetrical.
A
Pentaradially
22
Q
Nonvertebrate chordates do not form ________
or other bones.
A
vertebrae.
23
Q
What are hexapods?
A
Subphylum Hexapoda, which includes… --Class Insecta --Class Entognatha - 3 orders of wingless arthropods once thought to be insects: Collembola (Springtails) Protura (Coneheads) Diplura (Two-pronged bristletails)
Previously grouped together with the Class Myriapoda (millipedes and centipede) to form the ‘Uniramia’ – sometimes called the Antennata. Once thought to be a monophyletic group.
24
Q
What are some shared characteristics of insects and myriapods?
A
- -1 pair of antennae
- -1 pair of mandibles
- -2 pairs of maxillae
- -Uniramous limbs
- Head separate from trunk
25
What are the main characteristics of Class Insecta?
- -Body divided into three regions (tagmata):i.e. Head, Thorax, Abdomen
- -3 pairs of legs on thorax
- -No appendages on abdomen
- -Adults usually have 2 pairs wings (usually) on thorax
26
What are some key features of insects?
```
Wings
Exoskeleton
Feeding strategies
Reproductive strategies
life cycles
tracheal system
```
27
What are some wingless insects?
Silverfish
Apterygota: ‘Primitively’ Wingless
Derived species: wings lost secondarily … louse
28
What is an Apomorphy and give an example?
A new evolutionary development.
| e.g. wings
29
Wings are not
Homologous with any existing appendages.
30
What are wings?
- -Wings – thin, out-pockets of cuticle
- -Have sclerotizes veins (not true veins) between upper and lower layers
- -Venation has a fixed pattern according to species
31
What are some aspects of reproductive diversity?
Parental care
Viviparity
Parthenogenetic
Colonial
32
What are some lifecycles of insects?
Ametabolous
Hemimetabolous
Holometabolous
33
What is the effect of insects?
Pollination
Vectors
Pests + Parasites
34
What is the body of an insect divided in to?
3 regions
Head
Thorax
Abdomen
35
What are the features of each region?
3 pairs legs on thorax
No appendages on abdomen
Adults have 2 pairs wings
(usually) on thorax
36
What is an echinoderm?
Echinoderms are some of the most familiar sea shore invertebrates, particularly star fish and sea urchins
There are over 7000 species of echinoderms, and they are a major phyla within the superphyla deuterostome invertebrates.
The deuterostomia include the phylum Chordata (vertebrates, tunicates, lancelets) – we are in this phylum
Phylum Echinodermata (sea stars, brittle stars, sea lilies, sea urchins, sea cucumbers)
The phylum Hemichordata (acorn worms)
Phylum Xenoturbellida (two species of worm-like animals)
It is generally thought that the deuterostomes share a common ancestor
37
What are the main features of echinoderms?
All of the echinoderms are marine animals, and often live at great depths
The echinoderms, especially the holothurians (the sea cucumbers), but also asteroids (which are the star fish) are some of the most important deep sea benthic species (this means animals that live on the sea floor)
They have deuterostomous development
They have pentaradial symmetry, which is imposed on bilateral symmetry
They all have a calcareous endoskeleton (so this is a skeleton inside their body)
The endoskeleton is made up of separate plates or ossicles
They have a water vascular system and tube feet, also called their podia - and is what they use to move around
They usually have a complete gut, but this is lost in some species
They have a decentralised nervous system
38
How do echinoderms reproduce?
Most echinoderms reproduce by spawning
The fertilised eggs develop into planktonic free swimming larvae
These are very small, often <1mm long
They are very common in the plankton around the UK in the spring and summer
They have these so called arm structures to stop them from sinking in the water
Different classes of echinoderms have different arrangements of these arms
39
What are the properties of the echinoderm larvae?
They have bands of cilia, called ciliary bands, at various places around their bodies
These are for motility and for feeding
They have complete digestive tracts with a mouth, an oesophagus, stomach, intestine and an anus.
Although they appear complicated in shape, they are actually fundamentally bilaterally symmetrical
These features also apply to the sea cucumbers although the pentaradial
40
What type of symmetry do star fish have?
Star fish have pentaradial symmetry (5-axial symmetry) which is superimposed on bilateral symmetry. So the larval forms are bilaterally symmetrical and although the adults are pentaradial, it is thought that they retain some bilateral tendencies into adulthood because they exhibit a behavioural symmetrical plane
41
What happens when the free swimming larvae settle out of the plankton?
When the free swimming larvae settle out of the plankton there is a remarkable metamorphosis, and the bilateral symmetry is swamped by the pentaradial symmetry
42
What is the symmetry of all metazoan phyla?
All metazoan phyla (metazoans are multicellular eukaryotic organisms that undergo development from an embryo stage with three tissue layers, the ectoderm, mesoderm and endoderm; so these are all animals other than protozoans and sponges) are bilaterally symmetrical, apart from some animals which are radially symmetrical
43
What are stelleroidea?
These include the two subclasses, the Asteroidea and the Ophiuroidea
44
What is the Asteroidea class?
Asteroidea means star-like, and these are the star fish, or sea stars
There are around 1600 species
They are typically pentaradial, but some of them such as the sun star, or crossaster have many more axis of symmetry, up to 40 arms as you can see here
45
What is the Ophiuroidea class?
means snake-like, and incudes the brittle stars
These typically have 5 arms and occur in large aggregations
There are around 2000 species of these
46
What is the Echinoidea class?
means spine-like
They appear to have obvious radial symmetry, and again these are pentaradial
These are the sea urchins, heart urchins and sand dollars
There are around 1000 species
47
What are the Holothuroidea class?
are the sea cucumbers
There are about 900 species
They have pentaradial symmetry, which is only obvious if you look down on the tentacle end
These have become secondarily bilaterally symmetrical as well
Most echinoderms are adapted for life on rocks, but some Holothurians, mostly the deep sea Holothurians, are specialised for life in the sand and mud
They eat soft sediments
48
Why are Echinoderms unique?
Echinoderms are virtually unique in being the only major animal phylum that has no parasitic species – so they do not parasitize other animals – but they themselves are often parasitized, or hosts to commensal species (one species benefits from the interaction and the other is unaffected) for example by snails, bivalves, copepods, and sometimes crabs and fish
This is often the case for holothurians, which are bag-like and perfect for commensal species
49
What are Crinoidea?
means lily-like are so known as the sea lilies, or the feather stars
The sea lilies are stalked and the feather stars are not.
They also have pentaradial symmetry which is obvious when you look straight down at them
50
What are the Concentricycloidea?
These are the sea daisies
There is only one genus of sea dasies
They were discovered in the 1980s, and are now thought to be a type of specialised asteroid (star fish)
51
What do asteroids vary in?
Asteroids can vary in size from a few cm across to over a meter across: such as the huge sunflower star – but most are about 10-20 cm
52
Asteroid Anatomy
The upper surface of the asteroids is the aboral surface, and this has the anus more or less in the middle of it
The mouth is underneath
The underneath of the asteroids is the oral surface
The aboral surface and the anus of starfish is on the top, and the oral surface and the mouth of starfish is on the bottom.
--On the oral side there are grooves in the arms which are known as ambulacral grooves or walking grooves
The tube feet protrude from these ambulacral grooves
They walk using the tube feet
--They do not always have the tube feet protruding – they can be retracted and extended by the use of the water vascular system
53
What is the structure that we see in most Echinoderms?
The basic system of an oral surface with tube feet and a mouth, and the aboral surface with the anus can be seen in all of the Echinoderms
In the different classes the orientation of the animal is different
54
Even though all the Echinoderms have these two different surfaces, how are they organised?
Even though all the Echinoderms have these two different surfaces they are organised differently between classes, with elongation and shortening along different axes of the body
--For example in the Echinoids and the Holothurians the aboral surface is reduced to a very small proportion of the body surface
In the Holothurians there is a special elongation of the oral-aboral axis
55
What is present within the dermis of the body of the Echinoderms?
Within the dermis of the body of the Echinoderms there is a hard skeleton structure made of ossicles
The ossicles form part of the endoskeleton, providing rigidity and protection
They vary considerably across the echinoderms, but are all important for their various lifestyles
56
What are the properties of the ossicles in the asteroids?
In asteroids the ossicles are small and in the shape of crosses, rods or plates
Each ossicle is about 1 mm in size
They are believed to be a single crystal of magnesium rich calcite
The ossicles form a flexible and strong network
57
What are the properties of the ossicles in the ophiuroids?
```
In ophiuroids (brittle stars) the ossciles are similar to in asteroids but are even more developed
They can form vertebral ossicles which articulate against each other to form so called joint
```
58
How to the vertebral ossicles aid the arms of the Ophiuroids?
The vertebral ossicles make the arms of Ophiuroids very mobile
59
Ophiuroids are the most ____ of all the echinoderms
mobile
60
What are Ophiuroids capable of?
They are capable of rapid walking by pushing and pulling themselves with the movements of their arms
The tube feet in brittle stars are not used for locomotion as they are in the sea stars, as they are merely sensory tentacles and do not have suction capabilities
61
What are the properties of Holothurian ossicles?
The ossicles are very small, micrometers across and they lie separated from each other
The Holothurians have very well developed muscle layers
62
What are the edible Holothurians?
- --There are large fisheries for this in the sea in South East Asia, which supplies the Chinese markets
- --They are collected by diving and then are dropped in boiling water, which causes all the internal organs to shoot out
- --This is called self-evisceration and is a defence mechanism in echinoderms
63
What is the unique feature of Echinoderms and what are the properties of this?
The water vascular system is a unique feature of Echinoderms
It is a system of fluid filled tubes
It is especially well developed in the Asteroids and the Echinoids
It is used for locomotion
The internal arrangement of water-filled canals:
Near the middle of the aboral surface, there is an opening to the outside known as the madreporite; this is where the water enters and leaves
This is connected via the stone canal – called this because it is surrounded by ossicles
This descends within the animal to connect to the ring canal
The ring canal makes a ring around the mouth
From the ring canal, the radial canals lead off down each arm
These run on the oral surface of the arms in the ambulacral grooves
Off the radial canals are short lateral canals
These lateral canals connect to the podia (which are the tube feet), which have suckers on the end
They also have a flask shaped reservoir called ampulla, between the tube feet and the radial canals
64
Outline the properties of the Asteroid water vascular system?
On the oral surface (underside), you can see the radial canal, and the lateral canal connecting to the ampulla, and the podia or tube feet which are protruding through the holes in the ossicles of the arm
The podium is external and has muscles and sensory nerves, as well as mucus secreting cells
one individual asteroid may have thousands of these tube feet
The entire water vascular system is filled with fluid, and operates during locomotion as a hydraulic system
When the ampullae contract, a valve in the lateral canal shuts and fluid is pushed into the podium, which extends outwards
When the podium touches something, the centre of the terminal sucker is withdrawn, so that suction is created and the sucker holds on
This is helped by sticky secretions
To retract, the podia muscles contract, shortening the podium, forcing fluid back into the ampulla
During movement, each podium performs this same hydraulic mechanism in a stepping motion
The steps are highly coordinated so that the animal can move in a particular direction
The combined force of many hundreds of podia and the arms can be very strong, enabling most starfish to climb vertically
Some can generate forces large enough to open bivalve muscles and feed on them
65
What is well developed in Echinoids?
Echinoids have well developed tube feet, and if we look at the way in which these are organised it helps us to understand the way in which echinoids are arranged
The madreporite is at the top of the animal here
The holes along the outer surface mark the places where the tube feet leave the test – here are all the tube feet
They protrude through the ambulacral ossicles
66
Interally what are the features of the radial canals of the water vascular system?
Internally, the radial canals of the water vascular system run up the centre line of the ambulacral plates and the ampullae and podia lead off these via the lateral canals just like in the asteroids
--You can think about the Echinoid as being a pentaradial starfish with its arms all folded up on top of itself
--Walking on their tube feet is the main way echinoids get around, just like with the asteroids
67
What are the properties of Brittle stars?
Brittle stars have a similar arrangement of radial canals, but they do not move by tube feet, but by flexing their arms by pushing and pulling themselves along.
They have reduced podia – so they do not have as many tube feet and they are often reduced to sensory tentacles
This sort of athletic movement is also seen in the Crinoids (the sea lillies)
When they are at rest the sea lilies arms spread out, but when they are walking they come together so the animal becomes very vertical
Deep sea Crinoids ‘fly’ through the water by waving their arms
68
How do Holothurians (sea cucmbers) also move?
also move with their tube feet, but the podia are normally restricted to their sides
The bilateral symmetry which is secondary in the Holothurians means that the podia are not on the bottom of the animal, but more on the sides
The podia are normally very long
They walk in a very deliberate and slow manner
This is Scotoplanes, also called the sea pig, another deep sea Holothurian with very enlarged podia for locomotion
69
How do echinoderms feed?
Locomotion
Echinoderms as a group have a basically similar anatomical arrangement, but they have modified these for different lifestyles, as is the case for feeding
Asteroids are carnivores and feed on all sorts of invertebrates, especially bivalves, snails and crustaceans,
This rare asteroid can catch small fish that come to rest on its aboral surface: this is Stylasterias
But generally the asteroids are restricted to slow moving prey
70
What are some limitations to locomotion?
Locomotion using the tube feet and the water vascular system has its problems
Food in the deep sea is very patchy
Walking on podia is a very inefficient and slow way of finding food
Hence some deep sea Holuthurians ‘fly’ through the water, such as Pelegothuria which has a web of modified tentacles and uses muscles in this tunic to propel itself through the water
71
What is the feeding system of asteroids/
This is a vertical section through a starfish crossing the centre and one arm
The mouth leads to the cardiac stomach
This leads to the pyloric stomach, which has pyloric caecae branching off it running down each arm. These secrete enzymes that break down food.
Finally the pyloric stomach leads to the anus on the aboral surface
The cardiac stomach can be everted during feeding, which means it is pushed out of the mouth to directly surround the prey
Many starfish feed on large prey such as bivalves and crustaceans in this way
The starfish hunches over the prey, with its oral surface towards the prey and holds in in place with its podia, its tube feet
It then everts its stomach, which is very thin and very flexible and can completely surround the prey and even slip between the small holes in bivalves, as well as being able to open them with the arm muscles and suction of the tube feet
It exudes enzymes from the stomach to destroy the adductor muscles of the bivalves
Digestion is then completed internally, with the food being moved to the pyloric ceacae where it is absorbed and stored
The ceacae extend down the arms to give a large surface area for absorption and secretion of enzymes
72
How is waste voided in asteroids?
Waste is voided through the anus, but any bivalve shells in the stomach have to be voided through the mouth
In some asteroids this is the only way of feeding – they take things into the cardiac stomach and then everything is voided through the mouth because they do not have an anus.
73
What are most Echinoids?
Most Echinoids are herbivores – although sand dollars and heart urchins are suspension feeders or detritivores and live buried in sediment
74
What is the feeding system like inside a standard sea urchin?
The intestine is coiled around inside the animal, and ends at the anus on the aboral surface
The mouth is on the oral surface
The mouth has five teeth at its entrance
75
What is Aristotle's lantern?
Mouth structure
- --The teeth can be extended, retracted, and rocked from side to side by the lantern and are used to scrape and chew algae
- ---The five teeth grow continually from a growing point and are fed down the major ossicles of the lantern
- ---The major ossicles are known as pyramids
- ---The teeth grow at a rate of about 1 mm per week
76
What are the Lophophorates?
The Lophoporates are aquatic invertebrate animals, were previously thought to be deuterostomes. Before that, they were classified as protostomes. There is much debate over where they should be grouped.
Now the Lophophorates seem to have settled in as part of the protostomes.
--Lophophore means crest
---It is still uncertain how close these taxa are to each other
Even though we call them Lophopohorates, this is more for historical reasons than for valid taxonomical reasons
It is more of a convenience grouping, based on the presence of the Lophophore
It may be that the Lophophorates are a paraphyletic group
77
What is included in the phyla Lophophorates?
Three of the phyla, the Phoronids (also known as the horse shoe worms) the Ectoprocta (also known as moss animals) and the Brachiopods (also known as lamp shells), have only recently been recognised as Lophopohorates
The reason they are defined as Lophophorates is because they all share a unique feature called the Lophophore.
--Phoronida
(marine, benthic tube dwellers; “Horse-shoe worms")
---Ectoprocta
(aquatic, sessile, often colonial, bryozoans; “Moss animals")
---Brachiopoda
(marine, superficially like bivalve molluscs; “Lamp shells")
78
Outline aspects of the phylum-Phoronida.
----Phoronids live in tubes made of chitin
----There are two genera, and the most common of this is Phoronis
--There are about 15 species of Phoronis
--It is a worm about 5-15 cm long
--The most prominent feature is the Lophophore (the unique feature connecting all the Lophophorates)
---This is what it looks like in Phoronis - you can see why it means crest
In Phoronis it is U shaped, or horse shoe shaped
Which is why the common name for the Phoronids is the horse shoe worm
79
What is the lophophore covered in?
The lophophore is covered in cilia and this generates a water current that passes between the adjacent tentacles
Food particles are trapped in the lophophore by mucous which surrounds and covers it
The tentacles then pass the food down into the mouth
The mouth is here at the top of the animal at the base of the lophophore
80
What are aspects of the guts in the Phoronida?
---The gut is a very simple loop, which starts at the mouth, loops down through the animal, and comes back up to reach the anus which is also at the top of the animal outside the lophophore
81
Where are Phoronids commonly found?
Phoronids are commonly found in marine sediments and in mudflats
They usually form in aggregations often of many thousands of individuals
The aggregations form partly due to asexual reproduction, which they do by budding and fission
82
How many Ectoprocts are there?
There are about 4000 species of Ectoprocts. They are a major animal phyla in general, and are an important feature in the fossil record.
83
What are some properties of Ectoprocts?
All of these pictures show you Ectoprocts in their colony form
- ---Individually the Ectoprocts are very small, typically about 0.5 mm long
- ---They are most commonly found in colonies
- ---A colony is produced by asexual reproduction from a single sexually produced individual which has settled out of the plankton
- --The colonies look very plant-like and this is where they get their name the moss animals
84
What is simple in some Ectoprocts?
Some colonies are very simple strings of individuals
The most well known of these are the two dimensional colonies which form on kelp
These are Membranipora
85
What is another Ectoproct species and what are its properties?
is Electra pilosa
Each individual is known as a zooid
The zooids live in a calcareous box called a zooecium
The zooecium often has spines on it for protection
The zooid protrude out of the zooecium
The lophophore of the zooid comes out of the zooecium so that it can feed
They can withdraw the lophophore very rapidly using their fast retractor muscles
They are there to pull the animal back into the zooecium if they need to
If disturbed, they can shut the lid of the zooecium, which is called the operculum
The gut is relatively simple
The lophopore traps food and places it in the mouth
Then the gut runs from the mouth, around the animal, and then back up to the anus which again is near to, but outside, the lopophore
This zooid is not that far away from the phoronids – they look quite similar when looking at their individual form
Not all of the Ectoprocts have these calcareous boxes.
But most of them are colonial and live in a colonial form
This is one of the features of their success
86
What are the benefits of living in a colony?
Single individuals have some range of movement of its lophophore, which is helping it to find its food particles
The movements give a limited ability to pull the water towards them
The movement of water through their lophophore allows food particles to be collected
In contrast, the colonies are a lot more efficient at pulling in water
There are more of them, so they have combined action of the cilia on the lophophore which pull the water towards the animal
As a result of the combined action of many individuals, the water is pulled in, and pumped out in fountains called ex-current chimneys
By these mechanisms as a whole in the colony form, they are much more efficient at feeding and create a much greater through-flow of water which brings in more food particles for them to gather
Combined, they are much more efficient than lots of individuals on their own would be
Therefore the growth rates in the colony form are a lot faster, which is a really important feature of the ectoprocts
The species that they live on – i.e. kelp, can only last a few months, the Ectoprocts manage to go through many lifecycles while on that kelp due to their very fast growth rate
This is a reason for their success
87
Ectoprocts are important in
biofouling
88
What is fouling?
Fouling is the accumulation of microorganisms, plants, algae or animals on wetted surfaces
For example everything you see stuck to the bottom of a boat.
89
Where are foul Ectoprocts found?
Around 130 species of Ectoprocts have been found on the bottom of boats.
Ectoprocts also have the potential problem that they themselves can become fouled by other animals, so they can become encrusted by other plants, algae and animals.
As a result, they produce a compound called an anti-fouling agent
90
What is one anti fouling agent in Ectoprocts?
One of their anti fouling agents which stops other animals and plants encrusting them is called bryostatin 1
This is a really important anti-fouling agent and is under test as an anti-cancer drug
It has been isolated from this Ectoproct, Bugula neritina
91
Why are Ectoprocts also important?
Ectoprocts are also important because they are the intermediate host of proliferative kidney disease (PKD)
This is a very important parasitic disease of salmonids – which include trout and salmon
Professor Beth Okamura discovered the PKD DNA sequence and found that the PKD disease was in the infected fish, and also found the same disease in the freshwater Ectoprocts or Bryozoans
She found genes in the Bryozoans (same as Ectoprocts) that were very similar to the parasite that causes the disease that is found in the infected fish
Further experiments by other authors have confirmed that the parasites can be transmitted from the Ectoprocts to the fish
The DNA sequencing has identified that these freshwater Bryozoans are the intermediate host of the parasite that causes PKD in fish, and they transmit it to the fish, playing an important part in the lifecycle of the parasite.
92
What is the lifecycle of Tetracapsuloides bryosalmonae (which is the parasite that causes proliferative kidney disease in salmonids)
The parasite develops in the infected Ectoproct or Bryozoan
When the infection becomes overt, mature T. bryosalmonae spores are released, because large spore sacs are freely floating the in Ectoproct coelomic cavity.
These then infect salmonid fish and cause PKD. The rest of the lifecycle occurs in the fish, and spores are released from the fish which infect ectoprocts as a covert infection.
93
What are some Important features for defining a chordate?
Notochord
Dorsal hollow nerve chord
Gill slits
94
What are our closest invertebrate relatives?
The Urochordata and the Cephalochordata are our closest invertebrate relatives
There are around 300 species arranged into these many classes
95
Where are the Ascidians are commonly found?
found in tide pools, especially in the UK
They range from 1 mm – 60 cm in length
They are also known as sea squirts or tunicates
They are found in oceans at all depths, although they are common on rocky habitats
They can be solitary or cluster in groups, or they can be colonial
When they are colonial they consist of many individuals living in a gelatinous mix
96
What is the Tunic in Adult Ascidian?
The tunic is the bag surrounding the animal
It has two holes, the entrance or the oral siphon
And the exit, or the Atrial siphon
The tunic is leathery, and is made of a cellulose-like carbohydrate called tunicin
The tunic contains powerful antifouling compounds
Just as with the Ectoprocts, these are also being investigated for anti-cancer and anti-HIV drugs
Under the tunic are muscles
The muscles contract to flush the feeding apparatus with water
This is why they are called the sea squirt, because water squirts out of their atrial siphon in the process
97
How are the oral and atrial siphons positioned in the Adult Ascidian?
The oral and atrial siphons are set at angles from each other
This is important in allowing the water flows to be separated
Water is pumped by the action of the cilia on the pharangeal basket
This can produce a strong current
98
How are food particles trapped in the adult Ascidian?
- --The food particles are trapped in the mucus, and mucus is produced by the endostyle
- -The endostyle is a very important feature of the filter-feeding lower chordates, and is a ciliated fold in the pharyngeal wall which secretes mucus
- --Trapped food particles move to the gut, and waste is voided from the anus via the atrial siphon
99
What are most Ascidians?
Most Ascidians are hermaphrodites (so they have both male and female sex organs)
They shed both eggs and sperm into the water column to be fertilized
These then develop into free swimming tadpole larvae
The larvae only last from a few minutes to a few days depending on the species
100
What do Larval Ascidians share with the adult forms?
The features that they share with the adult form, include the oral siphon and the atrial siphon
They also have the pharyngeal sac, although this is called the branchial sac, and the endosytle
These are all common features with the adult form
They also have extra features, such as the notochord
The notochord is a stiff rod which takes the compressive force of the caudal muscles
This is how the animal moves to swim
There is also a neural tube, or a dorsal nerve chord
This is enlarged into a concentration of nervous system
It is a very simple nervous system
They have adhesive papillae on their anterior end, which enable them to settle and attach to a substrate during their metamorphosis
101
What are the features of the plankton?
For a very short period as a plankton, the tunicate larva becomes negatively phototactic and positively geotactic
These stay for a few days in their plankton form and then they move away from light and towards gravity, so they sink to the bottom of the ocean
They glue themselves to the bottom with the adhesive pads
There, they go through a rapid and extraordinary metamorphosis into their adult form, which can take only a few hours.
They completely change their structure
The oral siphon and the atrial siphon change position as the adult metamorphoses into the adult form
They are moving from a lateral position here in the larva to an anterior position in the adult
The notochord which is present in the larval form is lost in the adult from
102
What are some properties of Salps?
The salps can be solitary or colonial
They are very similar to the adult Ascidians
But they are not sessile like the adult Ascidians are, they are pelagic so they live free swimming in the water column
Solitary salp - Salpa
Colonial salp - Pyrosoma
103
What are some properties of Solitary salps?
They feed in a similar way to the Ascidians - they pump water into the pharynx in a gentle jet propulsion, to filter it
Well developed muscles in the tunic
They contract these muscles and use them to gently shoot through the water, and this is how they move
104
What are some properties of colonial salps?
They are an arrangement of individual zooids, which are embedded in a common gelatinous tunic
All of the zooids face the same way, so that the water is forced out of a common atrial chamber
And this is how they propel themselves along, again with gentle jet propulsion
They are bioluminescent and glow blue
That is why they are called fire body
105
Why is the Class Appendicularia (Larvaceansm) really important?
These are really important in the deep sea food chain, and are also a common class
106
What are properties of the Larvaceans?
They have a long tail which contains the notocord
Large head structure
They are only a few mm in length
Even though they are common, they are rarely seen because they live in a mucus house
The mucus house is made of mucus and jelly
107
How does water flow in Oikopleura?
The mucus house is a very complicated structure
It has chambers and filters and strains out plankton and water
Water flows in, and food is filtered and concentrated by the mucus net, with filtered water leaving via the excurrent opening
This allows larvaceans to feed on very small plankton that most other filter feeders cannot
The water is passed through the house by the tail
The house is continually shed and replaced, and one mucus house typically lasts about 3 hours
The larvaceans are so common in the open sea that the rain of the shed houses is a significant way for carbon to be transported from the shallow sea to the deep sea
So they play a really vital role in marine ecosystems
No equivalent to the adult stage of the ascidians
The larvaceans always look like this form shown here
This is an example of paedomorphosis
This means that sexually mature adults have exactly the same characteristics as those in their early developmental stages
108
What are some aspects of Cephalochordata?
The Cephalochordata are small and fish like animals, but they are not fish
They are about 5cm long
They are commonly called lancelets, amphioxus, or Brachiostina
They are common in shallow marine habitats and you can find them around the UK
You will normally see them with just their heads out
The rest of the body is usually buried
Fish like
Commonly called lancelets or amphioxus or Branchiostoma
Common in shallow marine habitats, UK
Usually lie buried with just their heads protruding
109
How do Cephalochordata filter water?
They feed by filtering water through a pharynx
They catch food particles by mucus produced by the endostyle
Water is drawn in via the mouth and exits via the pharyngeal gill slits
The pharynx has up to 200 slits, known as gill slits
Even though these are called gills, they are not for gas exchange, they are primarily for feeding
So gills in cephalochordate are for filter-feeding not for gas exchange
The mouth is anterior and the anus is posterior
They have very well developed muscles known as myotomes
There is only one mytotome shown in this diagram, but they are actually replicated along the whole body of the animal
In swimming they undulate just like a fish
The force of the muscles is taken by the notochord
The notocord in the cephalochordata is a very flexible rod which prevents the body shortening when the muscles contract
Propulsion is by the tail fin
They have some cephalisation, and they have an anterior brain and some sense organs
They have also developed a sort of circulatory system which includes vessels filled with ‘blood’ but no blood cells, and no central pump or heart; the so called blood is propelled by pulsation of several vessels
110
What are the chordates split into?
are split into the invertebrate chordates and the vertebrate chordates
111
The invertebrate chordates
| :The subphylum Urochordata:
Within the Urochordata the class Ascidiacae are the ascideans, the Thaliacea are the salps, and the Appendicularia are the larvaceans
112
The Lophophorates
```
Phoronids
----Horse-shoe worms
----Marine, benthic tube dwellers
Ectoprocts
----Moss animals
----Aquatic, sessile, often collonial, bryozoans
Brachiopods
----Lamp shells
----Marine, superficially like bivalve molluscs
```
113
Possible Deuterostomes, possibly Lophotrocozoans
Chaetognaths
- ---Arrow worms
- ---Marine and planktonic
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The Invertebrate Chordates
```
Subphylum Urochordata
----Ascidians
----Thaliacea (Salps)
----Appendicularia (Larvaceans)
Subphylum Cephalochordata
----Brachiostoma
```
