Chapter 30: Introduction to Animals

Diploblastic

(adjective: diploblastic) An animal whose body develops from two basic embryonic cell layers or tissues-ectoderm and endoderm. Compare with triploblast.

Triploblastic

(adjective: triploblastic) An animal whose body develops from three basic embryonic cell layers or tissues: ectoderm, mesoderm，and endoderm. Compare with diploblast.

determinate cleavage

(also called mosaic cleavage) is in most protostomes. It results in the developmental fate of the cells being set early in the embryo development.

Symmetry

-Asymmetry -Radial symmetry -Bilateral symmetry

Pattern of Development

1. Cleavage •Protosomes -Spiral -Determinate (a) Spiral cleavage •Deuterostomes -Radial -Indeterminate (b) Radial cleavage LOOK AT PPT SLIDES

Pattern of Development

2. Fate of blastopore during gastrulation

Pattern of Development

3. Development of coelom

acoelomate

A bilaterian animal that lacks an internal body cavity (coelom). Compare with coelomate and pseudocoelomate.

Presence and type of body cavity can be used to further describe triploblastic organisms.

A body cavity, also known as a coelom, is a space that opens up either within the mesodermal tissue or between the mesoderm and endoderm. It is not the same as the gut, which all triploblasts will have.

protosomes

A major lineage of bilaterian animals including arthropods, mollusks, and annelids. Sister group to deuterostomes.

deuterostomes

A major lineage of bilaterian animals that includes echinoderms and chordates; named for the embryonic development of the anus before the mouth (literally"second mouth"). Sister group to protostomes.

Nerve net

A nervous system in which neurons are diffuse instead of being clustered into large ganglia or tracts; found in cnidarians and ctenophores.

hydrostatic skeleton

A system of body support involving a body wall in tension surrounding a fluid or soft tissue under compression. Also called hydrostat. Compare with endoskeleton and exoskeleton.

Radially symmetrical animals have a diffuse network of neurons called a nerve net.

A typical nerve net is shown for the radially symmetrical hydra (a relative of jellyfish) on the right. The neurons (blue cells) are widely scattered throughout the entire organism, with no main branch or central concentration. Nerve nets work well for animals with radial symmetry, as they allow them to sense, respond and move equally in any direction.

The new organisms are typically all female and are genetically identical.

A variety of different animals are capable of producing young this way, from include invertebrates as well as some vertebrates, like this species of lizard.

Lastly, the coelom provides space that allows for the development of more complex internal organs.

Acoelomate organisms tend to have simpler bodies and less organ development than those with coeloms.

Centralized Nervous System

An aggregation of large numbers of neurons into clusters called ganglia in bilaterian animals. In vertebrates，the CNS consists of the brain and spinal cord. Compare with nerve net and peripheral nervous system (PNS).

pseudocoelomate

An animal having acoelom that is only partially lined with mesoderm. Compare with acoelomate and coelomate.

coelomate

An animal that has a true coelom, completely lined with mesoderm. Compare with acoelomate and pseudocoelomate.

Animals that have just two germ layers tend to have a "sac-like" body plan and an incomplete digestive tract.

An incomplete digestive tract has just one opening, as shown in this sea anemone diagram. Food enters the gut via this opening; and the gut itself it basically just a large sac that contains digestive enzymes. The food is broken down into monomers and absorbed, and any unused wastes pass out of the organism via the same opening they came in.

Coelom

An internal, usually fluid-filled body cavity that is completely or partially lined with mesoderm.

Some triploblasts do not have a coelom - these are called acoelomate organisms.

As shown in this diagram, the mesoderm forms a solid mass of tissue between the ecto- and endoderm.

Animals are split into three categories based on symmetry; they can be asymmetrical, radially symmetrical, or bilaterally symmetrical.

Basically, can we draw a line through the animal that will split it into two relatively equal parts?

If we look back to our phylogenetic tree, up top we can see that the earliest animals to evolve either lack symmetry (sponges) or have radial symmetry (Ctenophora and Cnidaria).

Bilateral symmetry evolved later and this large monophyletic group (the purple and orange branches) are called the "Bilateria". These are the animals that have bilateral symmetry, and it includes most of the animals that exist today. That's because bilateral symmetry has some advantages over the others that'll be discussed later.

There are three major patterns of asexual reproduction that we see in animals: budding, fragmentation and parthenogenesis. LOOK AT PPT SLIDES

Budding is shown in this image and occurs when a new daughter organism forms on the parent and eventually splits off. The new animal is formed solely via mitosis.

Triploblastic organisms tend to have a body plan that is described as a "tube within a tube", as well as a complete digestive tract.

Complete digestive tracts have two openings: a mouth and an anus.

Cell fate also differs. For protostomes, the new cells formed at this stage have a determinate fate - they have already started to specialize and can only develop into certain parts of the body.

Deuterostomes have indeterminate fate at this state - each cell at this early stage can still become ANY cell type of the body; they haven't begun to specialize yet.

The adult tissues that develop from these layers are listed here. LOOK AT PPT SLIDE

Ectoderm gives rise to the outermost tissue layers (outer layers of the skin) as well as nervous tissue. Endoderm gives rise to the inner lining of the digestive tract. Mesoderm produces pretty much everything else, including muscle, bone and most other internal organs.

Tissues arise during embryonic development; the embryo is the early stage of the new animal.

Embryonic tissue layers are called germ layers. These are layers of stem cells that will later differentiate into the adult tissue types.

All animals are heterotrophic via ingestion, but we have different methods of actually getting that food into our mouth. Common strategies include filter feeding (also called suspension feeding), where small particles are filtered out of the water and funneled toward the gut.

Fluid feeders are those that have a liquid diet and includes organisms who feed on plant fluids (nectar, etc, like this fly) or animal fluids (blood). These animals typically have piercing mouthparts that can be used like a straw. Other animals are mass feeders (this is what we are) - those that take in large chunks of solid food at a time.

For protostomes, the blastopore (the first opening) becomes the mouth of the GI tract while the 2nd opening becomes the anus. The term protostome literally means "first mouth".

For deuterostomes, the blastopore actually becomes the anus and the 2nd opening becomes the mouth. (Deuterostome means "second mouth").

Since the coelom forms between or within the mesoderm, it essentially separates the endodermal tissues from the ectodermal tissues. That allows independent movement of the body wall and the gut.

For example, the digestive muscles can contract to help digest food and move it along the tract, and those contractions can occur independently of the other muscles associated with outer body movements. Acoelomates in contrast have a solid mass of tissue from the endoderm to the ectoderm, so any muscle movement is transferred to the whole body.

The process of fertilization can occur in the external environment, or within the reproductive tract of the female.

For external fertilization, the gametes are released into the environment where they will fuse to form zygotes. The embryos will also typically develop in this external environment. This is usually only associated with aquatic animals, or with those who reproduce in the water.

Segmented body plans tend to be very successful - they lead to lots of specializations and diversity in animal bodies within these groups.

For instance with the vertebrates, the number and size of the vertebrae can differ between species, leading to differences in things like body length, neck length and flexibility. The arthropods have evolved all sorts of interesting body types based on variations in their segment, as we'll see later when we discuss that group.

For the worms and arthropods, the segmentation patterns are typically pretty obvious when looking at the body.

For instance, in this caterpillar (an arthropod) we see these repeating segments that extend down the body, with "feet" and spikes coming off each segment at regular intervals.

Fragmentation occurs when an animal splits or is split into multiple parts, and each part can grow can re-grow into a whole new animal. Certain worms as well as some other species are well-known for this.

For instance, planarian worms can be cut into 10 or more different pieces, and each piece will then regrow into a whole new worm!

We also use different terms to describe an animal's diet, and hopefully these will sound familiar.

Herbivores feed exclusively on non-animal foods (plants, fungi), carnivores feed exclusively on other animals (meat eaters) and omnivores have a diet of both plant and animal based foods.

This combination of features was so successful that we see it in most animals that exist today.

If you look back at that phylogenetic tree again, you can see that cephalization appears at the same branch as bilateral symmetry.

Germ Layers

In animals, one of the three embryonic tissue layers formed during gastrulation; gives rise to all other tissues and organs. See endoderm, mesoderm, and ectoderm.

cleavage

In animals, the series of rapid mitotic divisions, with little cell growth，that produces successively smaller cells (blastomeres) and transforms a zygote into a multicellular blastula.

In protostomes, a solid block of mesodermal tissue forms between the ecto- and endoderm and then splits to form the coelom.

In deuterostomes, the mesoderm forms as pockets that pinch off of the endodermal tissue.

Finally, ovoviviparous animals develop inside of an egg and receive nutrition from the egg yolk, but the egg is retained inside the mother's reproductive tract.

In other words, after fertilization occurs, the mother doesn't lay the eggs in the environment but keeps them in her body until the young hatch. Many fish species as well as certain snakes, like this copperhead, have ovoviviparous development.

The two remaining classifications - presence of body cavity and pattern of embryonic development - only apply to the triploblastic animals.

In other words, these are additional classification we use to categorize the triploblasts and we wouldn't use these categories when describing the sponges or diploblasts.

Where do fertilized eggs develop? There are three general patterns.

In oviparous animals, the fertilized eggs develop in the external environment. If the eggs are developing on land, they will have some protection against dessication (drying out). The eggs also contain yolk - a nutrient source that will supply the developing embryo with food.

Protostomes experience spiral cleavage, which we can see here as the embryo progresses from the 4-cell stage to the 8-cell stage.

In spiral cleavage, the new cells are produced at a diagonal angle to the vertical axis, so that each new cell sits in between the older ones. Deuterostomes experience radial cleavage, where each new cell sits directly on top of the parent cells.

Internal fertilization will occur in virtually all terrestrial animals (as the gametes would dry out if exposed to air), but many aquatic animals have internal fertilization too.

In these species, the sperm is passed from the male into the female's reproductive tract and fertilization occurs inside the female (like with us).

Mammals, as well as a few other species, have viviparous embryonic development.

In this case, the embryo is retained by the mother and receives nutrients directly from the mother instead of an egg yolk.

Bilaterally symmetrical animals have centralized nervous systems.

Instead of a widely scattered network, these systems typically have one or two main tracts of concentrated neurons running along the midline of the body, with smaller branches coming off that main line.

LOOK AT PPT SLIDES This diagram shows basic animal development in the embryonic stages. The zygote is the first cell of the new organism formed after fertilization. That zygote then begins to divide via mitosis, first forming a blastula, which is a hollow ball of hundreds of cells. That blastula then undergoes the process of gastrulation to produce a gastrula.

Invagination occurs as some of the outer layer of cells pushes into the middle of the embryo. This forms two distinct germ layers: the inner layer of cells becomes endoderm ("inner skin", shown in yellow), while the outer layer becomes ectoderm ("outer skin", shown in blue).

In some species, the fluid within the coelom is under pressure and acts as a hydrostatic skeleton (somewhat like the turgor pressure that develops in plant cells).

It provides a firm structures that muscles can push against to create more efficient movements.

This is the most common type of egg development in animals.

It will almost always be this type with animals who have external fertilization (where the egg is already in the external environment before it's fertilized), but it also common with internal fertilization, where the egg will be layed after fertilization occurs in the female.

Animals are characterized by their ability to move, but species vary in their method of moving. These images show various types of limbs, or limb-like structures, and other animals have no limbs at all. Don't worry about the terms you see on these images for now - we'll discuss some of these specific methods when we start getting into the various phyla.

LOOK AT PPT SLIDES

One of the other interesting patterns we see with many animals is metamorphosis, which is defined as a major changes in body form during their life cycle. Not all animals experience metamorphosis, but most people are familiar with this pattern in butterflies.

LOOK AT PPT SLIDES These images show the same species - the image on the left is the younger larval phase of the life cycle (the caterpillar), while the one on the right shows the adult. This dramatic change in form in common among insects, and we also see it in many amphibians - for instance with the change from tadpole to adult frog.

These images compare choanoflagellate protists to sponges, which were some of the earlier animals to evolve. To review a bit of phylogeny first, this piece of the eukaryotic phylogenetic tree shows the Opisthokonta lineage, which is the eukaryotic lineage that animals, fungi, and the choanoflagellate protists belong to.

LOOK AT PPT SLIDES FOR PHOTO

Sexual reproduction is also very common among animals. Unlike asexual reproduction, this process involves meiosis and fertilization, so the offspring are genetically unique.

Populations that reproduce sexually tend to have more diversity, which is advantageous for natural selection and survival of the species, particularly within changing environments.

We'll see example of both predator and parasites as we move forward, so I want to differentiate those terms here. Both predators and parasites feed on or off other organisms.

Predators are those that are typically larger than their prey (or similar sized) and kill the prey quickly. Parasites are usually much smaller than their prey and live on/in their prey (host) without killing them quickly. The tapeworm in this image is a good example of a parasitic animal - living in the intestine and feeding off the the nutrients taken in by the host. Parasites may weaken the host, and could eventually kill it in some circumstance, but not usually (the parasite is living off the host, so if the host dies, the parasite has lost it's meal).

LOOK AT ANIMAL PHYLOGENETIC TREE Note that the presence of the coelom is thought to have arisen at the same branch point as bilateral symmetry and triploblasty, although there is a question mark there.

Scientists are still uncertain about the evolutionary history of this trait, and among the bilateral animals we can see that the flatworms are acoelomate (they are thought to have lost their coelom sometime during their evolution). The others bilateral phyla shown here are either true coelomates or pseudocoelomates.

The animals make up a single monophyletic kingdom. Current estimates on total animal species sits between about 3-10 million, although it could be higher than that.

Scientists continue to discover new species of animals, particularly insects, on a regular basis.

In the adult organism, this allows specialization of the digestive tract.

Since food is moving through the gut in a single direction - entering at the mouth and exiting at the anus - different organs can develop that will process the food in specialized ways (i.e. esophagus, stomach, intestines).

All of these animals share several important characteristics. Firstly, all animals are multicellular. This distinguishes them from some of the single celled but heterotrophic protists (things like amoebas and paramecia).

Size varies from microscopic to very large (the blue whale, which is the largest living animal, can reach 30 m in length!).

All animals have a diploid life cycle.

Some can reproduce asexually though, and we'll talk more about that later.

These germ layers will later specialize into the adult tissues. All animals except sponges have these germ layers.

Some only have those two layers we just mentioned - the endoderm and ectoderm. Others have an additional 3rd germ layer called the mesoderm which forms in between the other two (shown in red).

Oviparous species may or may not provide parental care for the eggs.

Some parents will stay with and protect the eggs until they hatch while others leave them to fend for themselves.

Finally, all animals are motile at some point in their life cycle (they move).

Some species may be sessile as adults but motile during their larval phases. All animals except sponges have nerve and muscle cells that enable this movement.

Coelomate organisms contain a body cavity that develops within the mesodermal tissue. You can see these open areas bound on all side by the red mesoderm - that's the coelom. LOOK AT PPT SLIDES

Sometimes this group is called the eucoelomates, or true coelomates, to distinguish them from the third category...

Bilateral symmetry refers to animals in which there is only one plane of division that will give equal halves (one plane of symmetry).

That plane is typically along the center line of the animal from the head (anterior) end, to the tail (posterior) end. (Although not all bilateral animals have tails).

Animals that can reproduce via asexual reproduction will produce genetically identical offspring.

The advantage of asexual reproduction is that is usually takes less energy (no meiosis or gamete production, no mating).

The third category of triploblasts are pseudocoelomate organisms.

The animals do have a coelom, but it is only lined by mesoderm on one side (it sits between the mesoderm and endoderm).

The second thing that differs for proto- and deuterostome development is the fate of the blastopore.

The blastopore is the opening that forms during gastrulation, as some of the cells of the blastula migrate into the middle of the embryo and form the endoderm. The cavity that forms (which will become the gut) has a single opening at first - that is the blastopore.

Sponges are multicellular, and thus have multiple cell types that work together and are dependent on each other.

The choanocytes (also called collar cells) of the sponges closely resemble the choanoflagellate cells and gather and absorb food in a similar way. This close physical resemblance is the major reason why we consider these protists to be a sister group to the animals.

The smaller diagram on the left shows what happens during embryonic development that leads to this body type. Following gastrulation and the appearance of the 3rd germ layer (mesoderm, shown in pink), the primitive gut expands to the opposite side of the embryo and forms a 2nd opening.

The endoderm still lines the gut, but now it is a complete tract with both a mouth and an anus.

This body plan is typical of diploblastic organisms, and you can see the basic body shape within the embryo.

The endodermal cells frame the developing gut (called the archenteron), and there's a single opening for the gut.

All animals, except for sponges, have nervous tissue.

The evolution of nervous tissue and a nervous system was a huge asset to these organisms. Nervous systems use electrical signals and allow very fast communication with the external environment. It allowed animals to sense their environment in new ways as well as respond very quickly. In combination with muscle cells, which also work via electrical signaling and produce movement, nervous systems allow animals to move more rapidly than other organisms had done before, whether it was moving away from something (predator or unfavorable environment) or toward something (prey/food).

Cephalization

The formation in animals of a distinct anterior region (the head) where sense organs and a mouth are clustered.

Endoderm

The innermost of the three basic cell layers (germ layers) in most animal embryos; gives rise to the digestive tract and organs that connect to it (liver, lungs, etc.). Compare with ectoderm and mesoderm.

Segmentation refers to a body plan that contains repeated parts.

The major groups that show segmentation are the segmented worms (Phylum Annelida), the arthropods, and our own phylum - Phylum Chordata.

Mesoderm

The middle of the three basic cell layers (germ layers) in most animal embryos; gives rise to muscles, bones, blood, and some internal organs (kidney, spleen, etc.). Compare with ectoderm and endoderm.

Ectoderm

The outermost of the three basic cell layers (germ layers) in most animal embryos; gives rise to the outer covering and nervous system. Compare with endoderm and mesoderm.

Animalia plylas: -Porifera (sponges) -Ctenophora (comb jellies) -Cnidaria (jellyfish, corals, sea anemones) -Rotifera (rotifers) -Platyhelminthes (flatworms) -Annelida (segmented worms) -Mollusca (snails, clams, squid) -Nematoda (roundworms) -Anthropoda (insects, spiders, crustaceans) -Echinodermata (seas stars, sand dollars) -Chordata (vertebrates, tunicates) We'll be covering each of these phyla, with the exception of Ctenophora. LOOK AT ANIMALIA PHYLOGENETIC TREE

The outgroup up top of , the choanoflagellates, are not part of the animal kingdom, but they are considered our closest non-animal relatives among the protists.phylogenetic tree

In either case, the coelom provides various advantages for the animal.

The space that is created allows better circulation of oxygen and nutrients through the body, allowing organisms to grow larger.

To summarize those differences and assign terms - the phyla with two germ layers include the Cnidarians and Ctenophores, while all others have three (except sponges, which again don't have germ layers at all).

The term used to describe animals with two germ layers is diploblastic. Animals with three germ layers are triploblastic

LOOK AT PPT SLIDE Diploblastic organisms have simpler bodies - basically just an outer covering with nerve cells and an inner gut

The third germ layer - triploblasty - appears at the same point on the tree as bilateral symmetry and cephalization. Most of the animals that exist today have three layers and the more complex organ development that goes along with that.

Scientists are still trying to work out whether or not genes for segmentation are homologous among various groups, or whether it's completely convergent evolution (in other words, the genes may be homologous, but they may not be expressed in some groups).

Their morphological appearance in various groups does appear to be convergent though.

Sponges are only animals that can lack symmetry (they have asymmetry).

There is no line or plane of division we can make on a sponge that will divide it equally

The vast majority of animal species, and all phyla except 1, are classified an invertebrates.

These are the animals that lack a backbone (vertebral column) and includes things like sponges, jellies, worms, insects, spiders and more.

Many animals are also classified as detritivores.

These are those that feed on dead organisms. Like the decomposers of the food chain, they help recycle nutrients

The last strategy is called parthenogenesis. Parthenogenesis literally means "virgin birth", and this is where new animals develop from unfertilized eggs.

These eggs are typically produced via mitosis rather than meiosis and are capable of growing into a new organism without being fertilized by a sperm.

Animals undergo a diploid life cycle, and the only haploid phases will be the egg and sperm.

These gametes are produced via meiosis.

The combination of bilateral symmetry, a "head", and a centralized nervous system with neurons clustered in this head region allowed animals to sense and respond to their environment with more directed movements.

These organisms move through their environment headfirst, so its advantageous to have all these nerve cells concentrated on that end. Feeding structures (mouths, jaws, etc) also evolved to be positioned at the head, allowing animals to more actively feed/hunt.

There are two major groups of bilateral triploblasts based on these patterns: protostomes and deuterostomes.

These two groups are differentiated by three events that occur during their early embryonic development...

Choanoflagellates are not multicellular (although some are colonial, like the one shown here).

They have several physical characteristics in common with the sponges (which ARE classified as multicellular animals) and they share a similar feeding method.

Each choanoflagellate cell has a collar of microvilli as well as a single flagellum (choano = collar).

They use the motion of the flagellum to sweep food particles into the collar where they are filtered and absorbed.

In association with bilateral symmetry and the central nervous system, animals began to evolve cephalization - the appearance of a "head" (cephal = head).

This "head" end evolved additional clusters of concentrated neurons called ganglia - a primitive brain. Sensory neurons also came to be clustered at the head end of the animal; these are neurons that might sense light, smells, sounds, or touch.

Second, all animals are heterotrophic via ingestion.

This distinguishes us from the fungi. We ingest our food first and then digestion occurs internally, within our digestive system.

LOOK AT PPT SLIDE For us and the other vertebrates, our segmentation is seen in our vertebral column (note the repeated vertebrae that extend down our spine) as well as some aspects of our development.

This image shows a vertebrate embryo, and you can see the repeating blocks of tissue along the back side of the organism. Those blocks become bone as well as muscle tissue and nervous tissue.

LOOK AT PPT SLIDE (b) Coordinated muscle contractions result in locomotion.

This type of movement is shown here and is particularly important in soft-bodied animals that don't have an internal or external skeleton, like this worm.

Early Development of Animals

To review those stages we discussed earlier...the zygote is the first cell of the new organism that forms following fertilization. That zygote then begins to undergo a series of rapid mitotic cells divisions to produce a blastula (the hollow ball of cells). Those early cell divisions are called cleavage, and the first difference in protostomes vs deuterostomes involves these divisions.

Animals that have radial symmetry are those arranged around a central axis.

Two or more planes of division can give equal halves. In other words, they have at least 2 planes of symmetry, and any slice around the central axis produces equal halves.

Both asexual and sexual reproduction are common, but it depends on the species as to which they can do (and some can do both).

We'll take a look at the different pattern of asexual reproduction in second.

The vertebrates are those that have a backbone, and include fishes, amphibians, reptiles, birds and mammals.

While most of us are more familiar with the vertebrate animals, they comprise only a single phylum and <10% of all animal species. (The animal world is mostly insects!)

complete digestive tract

a clear beginning (the mouth) and a separate end (the anus). These animals take in food from the same opening they release waste.

Diploblastic organisms have... a. Simpler bodies and less organ development than triploblastic organisms b.More complex bodies and more organ development than triploblastic organisms c. Similar body types as triploblastic organisms

a. Simpler bodies and less organ development than triploblastic organisms Diploblastic organisms have simpler bodies - basically just an outer covering with nerve cells and an inner gut.

Humans are deuterostomes. During our early development... a. our cleavage pattern is radial b. our blastopore develops into our mouth c. our coelom develops via a splitting of mesodermal tissue

a. our cleavage pattern is radial

Are sea stars classfied as protosomes or deuterostomes? a. Protosomes b. Deuterosomes

b. Deuterosomes

indeterminate cleavage

cleavage in which all the early divisions produce blastomeres with the potencies of the entire zygote — compare determinate cleavage.

Coelomate organisms generally have......................than acoelomates. a. greater range of movement b. more complex organ development c. flatter bodies d. A & B e. A, B & C

d. A & B

radial cleavage

holoblastic cleavage that is typical of deuterostomes and that is characterized by arrangement of the blastomeres of each upper tier directly over those of the next lower tier resulting in radial symmetry around the pole to pole axis of the embryo — compare spiral cleavage.

Asymmetry

lack of equality or equivalence between parts or aspects of something; lack of symmetry.

Radial Symmetry

symmetry around a central axis, as in a starfish or a tulip flower.

blastopore

the opening of the central cavity of an embryo in the early stage of development.

gastrulation

the process by which a gastrula forms from a blastula.

spiral cleavage

the process by which cells of the early embryo divide and spiral around the pole-to-pole axis of the embryo - is the most common mode of animal development.

Bilateral Symmetry

the property of being divisible into symmetrical halves on either side of a unique plane.

Importance of Coelom

•Allows better circulation of oxygen and nutrients •Fluid acts as a hydrostatic skeleton

Importance of Coelom

•Allows independent movement of body wall and gut •Allows space for internal organs to develop

Pattern of Development

•Bilateral Triploblasts are divided into two groups: -Protosomes -Deuterosomes •Differentiated by three events during development

Symmetry and Nervous Systems

•Bilaterally symmetrical animals have centralized nervous systems (CNS) •Associated with cephalization (b) Central nervous system: clustered neurons in earthworm

Animal Evolution and Classification

•Body Symmetry •Number of embryonic tissue layers •Presence of body cavity •Pattern of embryonic development

Animal Evolution and Classification

•Body symmetry •Number of embryonic tissue layers •Presence of body cavity •Pattern of embryonic development

Phylogeny

•Choanoflagellate protists are closest living relatives of animals.

Presence of Body Cavity (Coelom)

•Coelomate organisms contain a body cavity that develops within the mesoderm

Tissue Layers

•Embryonic germ layers develop into adult tissues •Most animals, except sponges, have two or three distinct types of germ layers -Ectoderm: outer layer -Endoderm: inner layer -Mesoderm: middle layer

Fertilization

•External -Gametes released into environment •Internal -Sperm passed to female reproductive tract

Animal Diversity

•Feeding methods/food sources -Filter feeders, fluid feeders, mass feeders

Animal Diversity

•Feeding methods/food sources -Herbivores, carnivores, omnivores -Detritivores -Predators v. parasites •Predators are larger than their prey (usually) and kill quickly •Parasites are smaller than their prey and take nutrients from host without killing them (usually)

Sexual Reproduction

•Fusion of gametes •Offspring are genetically unique •Diploid life cycle •Higher genetic diversity results •Adaptive to changing environments

Germ Layers

•In general... -Ectoderm gives rise to outer coverings and nervous tissue -Endoderm gives rise to digestive tissue -Mesoderm gives rise to tissues in between

Segmentation

•Many animals have body plans based on repeated segments

Animal Diversity

•Method of moving

Kingdom Animalia

•Monophyletic •~3-10 million species •35 phyla -Invertebrates -Vertebrates

Major Characteristics

•Multicellular eukaryotes •Heterotrophic by ingestion (internal digestion) •Diploid life cycle; many can reproduce asexually •Motile at some point in their life cycle

Germ Layers

•No distinct layers -Sponges •Two germ layers (diploblastic) -Cnidarians, Ctenophores •Three germ layers (triploblastic) -All others

Embryonic Development

•Oviparous animals -Fertilized eggs deposited into external environment -Embryos nourished by yolk -May or may not have parental care

Embryonic Development

•Ovoviviparous animals -Embryo develops within egg (nourished by yolk), but egg is retained inside mother

Asexual Reproduction

•Partheogensis

Asexual Reproduction

•Produce genetically identical offspring •Strategies: -Budding -Fragmentation -Parthenogenesis

Early Development of Animals

•Produce germ layers

Animal Diversity

•Reproduction and life cycles -Asexual v. sexual -Metamorphosis

Body Plan and Digestive Tracts

•Sac body plan- incomplete digestive tract

Presence of Body Cavity

•Some organisms have a pseudocoelom, which is incompletely lined by mesoderm

Symmetry and Nervous Systems

•Sponges lack nervous systems •Radially symmetrical animals have nerve nets (a) Nerve net: diffuse neurons in hydra

Presence of Body Cavity (Coelom)

•Triploblastic organisms are classified by presence/absence of body cavity (coelom) •Acoelomate organisms do not contain a body cavity.

Body Plan and Digestive Tracts

•Tube w/n a tube - complete digestive tract

Embryonic Development

•Viviparous animals -Embryo develops in mother's body -Receive nutrition directly from mother