1. An introduction to the
diversity of animal life
Peter Shaw
RU
This is the jpg-free version to save space
2. Aim for today
To introduce you to the range of animal life on the planet. In one
lecture I can do no more than scrape the surface, but want to give you
a basic structure to carry in your head into which any animal may be
fitted. Forgive me for throwing a lot at you in one lecture!
This framework has a hierarchical structure (meaning it can be
shown as a dendrogram) founded in taxonomy.
Dendrogram
Taxonomy – the study of
the classification of life
forms.
3. Taxonomic hierarchies
These are about seeking common features unifying all the organisms in a
named group. The deepest split of all is between two ways of organising
cells – the eukaryotic cell (with a nucleus and organelles) and
prokaryotic cells (with DNA loops floating free in the cytoplasm). These
are divided into 5 kingdoms in modern systems:
Prokaryotes
Eubacteria
Archaebacteria
(Viruses would count as a 6th, if
you regard them as alive).
Eukaryotes:
Animals
Plants
Fungi
4. Phyla
In this course we will concentrate on just one kingdom, the animals.
Luckily there are few hidden catches here – it is usually pretty obvious
if a life form is an animal or not, though at the single celled level
things can get rather blurred. (Volvox is a single celled green,
photosynthetic entity which can ingest particulate food. It has good
claims to be both animal and plant).
The next level down from kingdom is the one that REALLY matters
for classifying animals. It is called Phylum, plural phyla.
(NOT fila, as a student once wrote in a failed exam paper…)
There are about 30 phyla, each with a deep underlying similarity of
body form. Once you can place an animal in its phylum you have
made an excellent start towards understanding its anatomy.
5. The full hierarchy
Kingdom - animalia
Phylum - mandibulata
Class - Insecta
Order - Collembola
Family - Entomobryidae
Genus Entomobrya
Species Entomobrya nivalis
Species - the basis of taxonomy, dignified by a Latinised binomial =
the scientific name: Homo sapiens, Apodemus sylvaticus, Lumbricus
terrestris.
(I dislike the term “latin name”, since it is not Latin but merely
latinised. Others find it acceptable, but I would encourage ‘Scientific
name’)
6. How to write a scientific name!
So many students get this wrong that I want to tell you
now, at the start of your careers, how to write these
names. Remember that getting it wrong is equivalent
to saying “I have not been formally trained in
biology”.
Homo sapiens OR Homo sapiens
When writing by hand
underline the name.
1st name has a capital letter, 2nd does not
On a PC make the font italic
7. One cell or many?
We start dividing up animals here.
Some animals have just one cell – many others have
large numbers of differentiated cells.
1 cell - Protozoa Many cells – parazoa and metazoa
8. The Protozoa – the single celled
animals
In fact many of these are photosynthetic and are claimed as plants by
botanists, while some are both photosynthetic and carnivorous! The
animal -plant - fungus split does not make sense at this level.
Old system: exclude green species, lump the rest in
Phylum protozoa, which has 4 classes:
ciliates (Paramecium caudatum) – many small cilia
flagellates (Euglena, Trypanosoma) – one big cilium
(flagellum)
Rhizopoda (Amoeba proteus) – no cilia
+ a less well known class of parasitic species: Sporozoa
(Plasmodium vivax)
9. New version – kingdom Protozoa
Instead of the drastic shoe-horning described above, the current
version is to regard all single-celled organisms as belonging to
the kingdom Protozoa with many phyla (27 at last count!)
This is probably more realistic, but much harder to remember.
10. Sponges – Phylum parazoa
These are essentially colonial protozoa, whose colonies are reinforced
with solid spicules of various shapes and composition. Silica SiO2 and
Calcite CaCO3 are the commonest.
11. Parazoa are exclusively aquatic, mainly marine, and
live by filter feeding. The feeding cells are called
choanocytes, which incorporate a central flagellum
pumping water through the sponge, and the water
passes through a collar of cilia-like filtering
projections. The other main cell type is ameoba-like,
making the supporting tissues and moving nutrients
around.
Typically sponges suck water in from around
their bodies and exhale it from a common
central siphon. Due to their diffuse form, and
often variable colour, identifying them is often
difficult / impossible in the field and relies on
microscopic examination of spicules.
12. The next level up in organisation takes us to the group of animals that
used to be classed as phylum coelenterata (jellyfish, anemones and
sea gooseberries). These are now split into 2 phyla, based on deep
differences in design of their their stinging cells:
Cnidaria – jellyfish and anemones
Ctenophora – sea gooseberries.
1 cell - Protozoa
No clear tissues: parazoa
Metazoa: These are animals with fully differentiated
tissues, including muscles and nerves.
Tissues: metazoa
Many cells
13. Phylum Cnidaria (radially
symmetric, 2 cell layers in body)
Jellyfish and allies. These alternate 2 phases in their life cycle: the
free-living medusoid phase (“jellyfish”), and a sessile hydroid
phase.
Budding
Eggs and sperm
Medusoid
phase
Hydroid phase
14. This phylum feeds by capturing planktonic
food using tentacles armed with a cnidarian
speciality, the class of stinging cell called
nematocysts. Some are entangling, some
inject barbed points to anchor, some inject
toxins.
A few a lethal to humans - NEVER EVER swim with
box jellies (sea wasps, class Cubomedusae).
A cnidocyte
(=nematocyst)
15. Bilateria: this comprises c. 25 phyla all
with bilateral symmetry (at least as larvae)
and 3 layers of cells in the embryo.
1 cell - Protozoa
No clear tissues: parazoa Tissues: metazoa
Radial symmetry
2 cell layers in embrya
Phyla cnidaria and ctenophora
Bilateral symmetry
3 cell layers in embryo
Remaining animal Phyla
Many cells
16. Phylum Platyhelminths
The simplest of these phyla are the flatworms,
platyhelminths. These have no body cavity
(acoelomate), and a “bottle gut” (ie mouth and
anus are the same orifice).
A few are internal parasites, ie liver fluke
Fasciola hepatica. Bilharzia is caused by a
flatworm Schistosoma that lives inside blood
vessels - a serious medical problem.
<1mm deep
Combined mouth and anus, leading into gut
Many are free living, the planaria, and are active hunters. One recently
introduced species from New Zealand is a serious earthworm predator -
Arthiopostioa triangulata. M+F
Schistosoma
17. Body cavities
None of the phyla mentioned so far have any internal fluid-filled
body cavities. In fact most animal phyla do – these turn out to be
highly important for making sense of phyla.
Bilateral symmetry
3 cell layers in embryo
No body cavity
Flatworms
Phylum platyhelminths
(and the closely related
phylum nemertini,
bootlace worms.)
Has body cavity
Lined with cells
Coelomate phyla
Not lined with cells
Pseudocoelomate phyla
18. Pseudocoelomates, especially
phylum nematoda, the
roundworms
There are quite a few rather obscure phyla here, mainly of
tiny (<2mm) and unfamiliar creatures that live in the water
between grains of sand, in sediments etc – Phyla rotifera,
gastrotricha and others (look up “minor pseudocoelomate
phyla”). There is only one of these phyla that is really
significant in terms of species richness.
These are the roundworms, phylum nematoda.
19. Nematodes: Almost all have the same body shape - round, pointy at
both ends. (A very few plant parasitic species look like balloons, being
immobile and full of eggs).
All have a thick collagen body wall retaining a high internal hydrostatic
pressure - they are almost impossible to squash under normal
circumstances.
Most of you here will have been infected with nematodes. Luckily the
commonest nematode in humans is tiny and harmless - the pinworm
Enterobius vermicularis.
Nematode eggs are very tough (collagen wall again) and stay viable for
months or years.
Phylum nematoda – the
roundworms
20. The big 5 coelomate phyla
There are about 10 phyla in which the basic body design involves a
body cavity lined with cells (called a coelom), but of these I will
only cover 4 today – these are the important common ones. One
grouping is probably 3 distantly related phyla.
Phylum annelida – the segmented worms
Phylum mollusca: snails and allies
Phylum echinodermata – starfish and allies
Phylum (superphylum?) arthropoda – insects, spiders and
crustaceans.
Phylum chordata – everything with a backbone (including us)
21. Phylum Annelida – the segmented worms.
The most familiar of these is the common earthworm, Lumbricus
terrestris.
(In fact, ecologically, this is one of the oddest annelids!)
All have true metameric segmentation, with each segment carrying gut,
musculature and part of the nerve cord. There is often some
differentiation of segments, ie the collar (clitellum) of earthworms.
Lumbricid showing
clitellum
22. The classes are:
Class chaetopoda - annelids with chaetae:
order Polychaetes - marine worms, often very spiky
with chaetae on lateral projections called parapodia
(These are the great majority of annelids).
order oligochaeta - freshwater / terrestrial,
small chaetae, earthworms etc.
Class hirudine - leeches; predators /
ectoparasites with anterior + posterior
suckers
23. Phylum Mollusca – snails and allies
These have a soft, mucus-covered body with a muscular foot, often with
a calcareous shell.
Class Lamellibranchs (=Bivalves) -
aquatic filter feeders, using their
gills to capture suspended food
particles.
24. Class gastropoda - limpets, slugs
and snails. Originally marine
grazers, have emerged to become
major terrestrial herbivores.
Phylum Mollusca – snails and allies
25. Class Cephalopoda - octopuses, squids, ammonites, nautilus (ie
common octopus; Octopus vulgaris). Very different to other
molluscs, with the muscular foot becoming 8-10 tentacles for food
capture. They have independently evolved an eye almost identical to
vertebrates, and seem to be the most highly intelligent invertebrates.
They also include the largest invertebrates - a giant squid can be >5m
long, with another 10m of tentacles.
Phylum Mollusca – snails and allies
26. Phylum Echinodermata – starfish
and allies
All have an unexplained pentagonal symmetry, and a
calcite exoskeleton supporting a complex system of
tube feet used for slow locomotion. Any fossil – if it
is pentagonal, it’s an echinoderm!
Echinoidea - sea urchins
Ophiuroidea - brittle stars
Holothuridae - sea cucumbers
Crinoidea - feather stars
Classes
Asteroidea - starfish
27. phylum Arthropoda – insects,
spiders and crustaceans
This is the biggest phylum in existence.
All these animals have a hard external skeleton and jointed legs.
(‘Arthropod’ means jointed foot or limb). For many years these
were treated as one huge phylum with three clear subphyla. More
recently various lines of work, notably DNA analyses, suggest that
the differences in these 3 subphyla are so great that they probably
evolved the ‘armoured’ body form independently, and should be seen
as 3 distinct phyla.
Note that there is continuing disagreement about whether arthropods
are a phylum or a super-phylum. The recent merge with nematodes
into ecdysozoa strengthens the case for ‘phylum’.
28. phylum Arthropoda
(all have exoskeleton)
Sub-phylum
Mandibulata
Mouthparts are
mandibles, 1 pair
antennae.
Insects, millepedes,
centipedes etc
Insects have 3 pairs
of legs
Sub-phylum
Chelicerata
Mouthparts are
claw-like
(chelicera), no
antennae.
Spiders, mites, and
horseshoe crabs.
Sub-phylum
Crustacea
Mouthparts are
mandibles, 2 pairs
antennae.
Crabs, shrimps,
lobsters, woodlice
etc.
All have calcified
cuticle.
29. Our phylum – the chordates
All chordates have a dorsal nerve cord running along the body.
There is an anterior swelling (‘brain’), and segmentalised body with
segmented blocks of muscle. Unlike the arthropods and molluscs
the brain does not encircle the gut – happens to be a good design for
large body sizes.
Most chordates have bones along their nerve cord, making them
vertebrates. Not all – some of our phylum are invertebrates!
A hagfish – a boneless chordate, here tying
A knot in itself.
30. Sea squirts (subphylum urochordates) have a larval
form that is built much like a tadpole, barring a lack
of bone, and are clearly from the chordate mould. But
the adults forsake this for a sedentary life filtering sea
water through a mucus net. There are a few other less
well known invertebrate chordates.
Our phylum – the chordates
Adult sea squirt – Ciona intestinalis
Larval
tunicate,
showing
same
notochord
anatomy as
mouse
31. Vertebrates
The bony animals divide neatly into 5 classes, all of which
you will recognise:
Pisces (fishes)
Amphibia – frogs newts etc (smooth skin)
Reptiles – lizards etc (scales)
Birds (feathers)
Mammals (us, whales and everything else warm and furry)
Inevitably, the harder one looks at the fossil record, the less
clear-cut these boundaries become!
