An introduction to the diversity of animal life

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An introduction to the diversity of animal life
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Aim for today
To introduce you to several characteristics found
in animals and 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. This framework has a
hierarchical structure (meaning it can be shown
as a dendrogram) founded in taxonomy.
Taxonomy the study of the classification of
life forms.
Dendrogram
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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 Eukaryotes Animals Plants Fungi Prokary
otes Eubacteria Archaebacteria (Viruses would
count as a 6th, if you regard them as alive).
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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. 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.
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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.
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How to write a scientific name!
Homo sapiens OR Homo sapiens
1st name has a capital letter, 2nd does not
When writing by hand underline the name.
On a PC make the font italic
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• Concept 32.1 Animal are multicellular,
  heterotrophic eukaryotes with tissues that
  develop from embryonic layers
• Several characteristics of animals
• Sufficiently define the group

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• Their bodies are held together
• By structural proteins such as collagen
• Nervous tissue and muscle tissue
• Are unique to animals

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Reproduction and Development

• Most animals reproduce sexually
• With the diploid stage usually dominating the
  life cycle

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• After a sperm fertilizes an egg
• The zygote undergoes cleavage, leading to the
  formation of a blastula
• The blastula undergoes gastrulation
• Resulting in the formation of embryonic tissue
  layers and a gastrula

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• Early embryonic development in animals

Figure 32.2
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• All animals, and only animals
• Have Hox genes that regulate the development of
  body form
• Although the Hox family of genes has been highly
  conserved
• It can produce a wide diversity of animal
  morphology

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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
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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) Rhizopod
a (Amoeba proteus) no cilia   a less well
known class of parasitic species Sporozoa
(Plasmodium vivax)
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  Ciliates are covered in hundreds of tiny motile
hairs cilia (sing. cilium). Are common in
freshwater, also benign gut inhabitants.   flagell
ates move by a small number of long motile hairs
flagellae (sing. flagellum). Free living, also
rumen flora and some gut parasites.   Rhizopoda
free living in sediments etc, moving by slow
protrusion of pseudopodia. A few are nasty
parasites (Entamoeba dysenterica, Naegleria
spp.)   Sporozoa (Plasmodium vivax causes
malaria, the biggest killer in human history)
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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.
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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.   They 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.
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Metazoa These are animals with fully
differentiated tissues, including muscles and
nerves.
Many cells
1 cell - Protozoa
No clear tissues parazoa
Tissues metazoa
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.
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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.
Both feed 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).   The main classes
are Scyphozoa jellyfish, Aurelia aurita in
the common UK moon jelly (harmless to
humans) Anthozoa sessile forms sea anemones,
corals, sea fans Hydrozoa various medusoid
radiations, often with several body forms fused
into one animal ie Physalia physalis, the
infamous, portugese man owar (avoid!).
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Bilateria this comprises c. 25 phyla all with
bilateral symmetry (at least as larvae) and 3
layers of cells in the embryo.
Many cells
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
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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).
lt1mm 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. 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.
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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
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Pseudocoelomates, especially phylum nematoda, the
roundworms
There are quite a few rather obscure phyla here,
mainly of tiny (lt2mm) 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.
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Phylum nematoda the roundworms
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.
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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)
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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.   The classes
are Class chaetopoda - annelids with
chaetae order Polychaetes - marine worms, often
very spiky with chaetae on lateral projections
called parapodia (Beware divers do not
touch) order oligochaeta - freshwater /
terrestrial, small chaetae   Class hirudine -
leeches predators / ectoparasites with anterior
posterior suckers.
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Phylum Mollusca snails and allies
These have a soft, mucus-covered body with a
muscular foot, often with a calcareous
shell.   Class gastropoda - limpets, slugs and
snails. Originally marine grazers, have emerged
to become major terrestrial herbivores. Class
Lamellibranchs (Bivalves) - aquatic filter
feeders, using their gills to capture suspended
food particles.   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 gt5m
long, with another 10m of tentacles.
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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, its an
echinoderm!   Classes Asteroidea -
starfish Echinoidea - sea urchins Ophiuroidea -
brittle stars Holothuridae - sea
cucumbers Crinoidea - feather stars   Starfish
are predators, echinoids are herbivores,
holothuridae are detritivores, the remainder
filter feeders.
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Superphylum 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. Forgive me
if I still use the term Arthropod! It may yet
come back, and if it doesnt it remains a handy
abbreviation.
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Superphylum Arthropoda (all have exoskeleton)
Phylum Crustacea Mouthparts are mandibles, 2
pairs antennae. Crabs, shrimps, lobsters,
woodlice etc. All have calcified cuticle.
Phylum Chelicerata Mouthparts are claw-like
(chelicera), no antennae. Spiders, mites, and
horseshoe crabs.
Phylum Mandibulata Mouthparts are mandibles, 1
pair antennae. Insects, millepedes, centipedes
etc Insects have 3 pairs of legs
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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! 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.
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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!
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• Concept 32.2 The history of animals may span
  more than a billion years
• The animal kingdom includes not only great
  diversity of living species
• But the even greater diversity of extinct ones as
  well

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• The common ancestor of living animals
• May have lived 1.2 billion800 million years ago
• May have resembled modern choanoflagellates,
  protists that are the closest living relatives of
  animals

Figure 32.3
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• Was probably itself a colonial, flagellated
  protist

Figure 32.4
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• Concept 32.3 Animals can be characterized by
  body plans
• One way in which zoologists categorize the
  diversity of animals
• Is according to general features of morphology
  and development
• A group of animal species
• That share the same level of organizational
  complexity is known as a grade

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• The set of morphological and developmental traits
  that define a grade
• Are generally integrated into a functional whole
  referred to as a body plan

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Symmetry

• Animals can be categorized
• According to the symmetry of their bodies, or
  lack of it

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• Some animals have radial symmetry
• Like in a flower pot

Figure 32.7a
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• Some animals exhibit bilateral symmetry
• Or two-sided symmetry

Figure 32.7b
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• Bilaterally symmetrical animals have
• A dorsal (top) side and a ventral (bottom) side
• A right and left side
• Anterior (head) and posterior (tail) ends
• Cephalization, the development of a head

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Tissues

• Animal body plans
• Also vary according to the organization of the
  animals tissues
• Tissues
• Are collections of specialized cells isolated
  from other tissues by membranous layers

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• Animal embryos
• Form germ layers, embryonic tissues, including
  ectoderm, endoderm, and mesoderm
• Diploblastic animals
• Have two germ layers
• Triploblastic animals
• Have three germ layers

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Body Cavities

• In triploblastic animals
• A body cavity may be present or absent

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• A true body cavity
• Is called a coelom and is derived from mesoderm

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• A pseudocoelom
• Is a body cavity derived from the blastocoel,
  rather than from mesoderm

Figure 32.8b
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• Organisms without body cavities
• Are considered acoelomates

Figure 32.8c
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Protostome and Deuterostome Development

• Based on certain features seen in early
  development
• Many animals can be categorized as having one of
  two developmental modes protostome development
  or deuterostome development

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Cleavage

• In protostome development
• Cleavage is spiral and determinate
• In deuterostome development
• Cleavage is radial and indeterminate

Figure 32.9a
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Coelom Formation

• In protostome development
• The splitting of the initially solid masses of
  mesoderm to form the coelomic cavity is called
  schizocoelous development
• In deuterostome development
• Formation of the body cavity is described as
  enterocoelous development

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Fate of the Blastopore

• In protostome development
• The blastopore becomes the mouth
• In deuterostome development
• The blastopore becomes the anus

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• Concept 32.4 Leading hypotheses agree on major
  features of the animal phylogenetic tree
• Zoologists currently recognize about 35 animal
  phyla
• The current debate in animal systematics
• Has led to the development of two phylogenetic
  hypotheses, but others exist as well

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• One hypothesis of animal phylogeny based mainly
  on morphological and developmental comparisons

Figure 32.10
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• One hypothesis of animal phylogeny based mainly
  on molecular data

Figure 32.11
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Points of Agreement

• All animals share a common ancestor
• Sponges are basal animals
• Eumetazoa is a clade of animals with true tissues

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• Most animal phyla belong to the clade Bilateria
• Vertebrates and some other phyla belong to the
  clade Deuterostomia

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Disagreement over the Bilaterians

• The morphology-based tree
• Divides the bilaterians into two clades
  deuterostomes and protostomes
• In contrast, several recent molecular studies
• Generally assign two sister taxa to the
  protostomes rather than one the ecdysozoans and
  the lophotrochozoans

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• Ecdysozoans share a common characteristic
• They shed their exoskeletons through a process
  called ecdysis

Figure 32.12
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• Lophotrochozoans share a common characteristic
• Called the lophophore, a feeding structure
• Other phyla
• Go through a distinct larval stage called a
  trochophore larva

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Chapter 33 Invertebrates- sponges

• Overview Life Without a Backbone
• Invertebrates
• Are animals that lack a backbone
• Account for 95 of known animal species

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• A review of animal phylogeny

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• Exploring invertebrate diversity

Figure 33.3
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• Exploring invertebrate diversity

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• Exploring invertebrate diversity

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• Sponges are sessile and have a porous body and
  choanocytes
• Sponges, phylum Porifera
• Live in both fresh and marine waters
• Lack true tissues and organs

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• Sponges are suspension feeders
• Capturing food particles suspended in the water
  that passes through their body

Figure 33.4
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• Choanocytes, flagellated collar cells
• Generate a water current through the sponge and
  ingest suspended food
• Most sponges are hermaphrodites
• Meaning that each individual functions as both
  male and female

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• Concept 33.2 Cnidarians have radial symmetry, a
  gastrovascular cavity, and cnidocytes
• All animals except sponges
• Belong to the clade Eumetazoa, the animals with
  true tissues
• Phylum Cnidaria
• Is one of the oldest groups in this clade