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Animals are multicellular eukaryotes. Unlike and fungi,most are motile (can move around), have amazing sensory ability, and capable of very complex behaviours.
Phylogeny and classification
Phylogeny and classification
The common ancestor of animals may have been a colonial, flagellated protist from 700 million years ago
Colonial protist indented (likely for feeding purposes).
Biologists have theorized that a spherical arrangement of cells in a colony may have become indented, forming a hollow cavity, which would have helped the organism capture and digest food (Figure 3). This same arrangement and process can be observed in the embryonic development of animals today. This double-layered arrangement of cells with a lining of specialized digestive cells is very similar to that of sponges, the simplest of all modern animals
Hollow feeding cavity formed and specialized feeding cells developed
Some animals developed specialized nerve cells
Figure 3. Scientists believe that animals evolved from colonial protists. The protists developed a hollow body cavity and specialized feeding cells. Over time, the colonies evolved into multicellular organisms with specialized tissues.
A key early innovation among animals was the development of nerves— specialized cells for coordinating movements and sense changes in environments. Animals in the Porifera phylum, like modern sponges, are the only ones that do not have this key animal feature. Another major division among animal phyla is between those with radial symmetry and those with bilateral symmetry. Animal bodies with radial symmetry are regularly arranged around a central axis, like the spokes of a wheel. Jellyfish, for instance, have radial symmetry. The bodies with bilateral symmetry, like humans, have left and right sides that are mirrored of each. As shown in Figure 4, bilaterally symmetrical animals also have different dorsal (upper) and ventral (lower) surfaces, and an anterior (front) and posterior (back) end.
radial symmetry: a symmetry around a central axis
bilateral symmetry: a symmetry around a midline
Figure 5. A phylogenetic tree of the Animal Kingdom is based on recent evidence from genetics and molecular biology. The tree shows 10 of the 17 animal phyla.
Bilaterally symmetrical animals are further divided into 2 major branches. The
protostomes and deuterostomes are distinguished by different patterns of embryonic
development. Humans belong to the deuterostome phylum Chordata. The Chordata
are mostly vertebrates—animals with a dorsal backbone or notochord (fish, amphibians, reptiles, birds, and mammals). All other animals are invertebrates.
Figure 5 is a phylogenetic tree based on recent evidence from genetics and molecular biology. It illustrates one current hypothesis about the evolutionary relationships
of 10 major phyla of animals. There are 7 more animal phyla not shown on the tree, but they include relatively few species.
protostome an animal with bilateral symmetry; during embryonic development, the mouth forms before the anus
deuterostome an animal with bilateral symmetry; during embryonic development, the anus forms before the mouth
vertebrate an animal with a backbone or a notochord
notochord a flexible rod found in some chordates; in most modern chordates it is replaced by vertebrae during embryonic development
invertebrate an animal that does not have a backbone; the great majority of animal species are invertebrates
Characteristics
Characteristics
All animals are multicellular heterotrophs that use oxygen for aerobic respiration. Unlike plants and fungi, animal cells do not have cell walls. Their cell membranes are in direct contact with each other. Animals feed on plants, fungi, protists, and each other. A number of animals also have symbiotic relationships with autotrophs that provide a supplementary source of food.
Cell Specialization and Germ Layers
Cell Specialization and Germ Layers
The nerve cells developed in first animals are one of the many specialized cell types in animals. These cells become specialized in embryonic development. A way that animal phyla are distinguished is by their number of germ layers of the members. Germ layers are the cell layers in a developing embryo giving rise to specialized tissues.
There are 3 germ layers:
ectoderm (ecto means “outer” and derm means “layer”)
endoderm (endo means “inner”)
mesoderm (meso means “middle”)
The ectoderm gives rise to the skin and nervous system. In some complex animal ectoderm cells produce shells, scales, feathers, hair, and nails, forming the inner lining of the gut, and in the respiratory system in some organisms. The mesoderm gives rise to the circulatory, reproductive, excretory, and muscular systems.
Coelom
Coelom
A coelom is a fluid filled body cavity providing space for the development and suspension of organs and organ systems
Develops from the mesoderm
a) Acoelomate:
flat bodies, softer, less rigid
Flatworms, jellyfish, corals
b) Coelomate:
rounder bodies, firmer, more rigid
Insects, humans, fish
Simplest Invertebrate Organisms
Simplest Invertebrate Organisms
Phyla Porifera and Cnidaria include the simplest invertebrate animals. The Porifera has about 8k sponge species. Figure 7 shows that sponges have a simple body plan with flagellated cells, called choanocytes, lining a central cavity. The flagella create a continuous current of water passing through pores in the body wall and exit through large openings at the sponge's top. Choanocytes capture the food particles entering with water. Porifera are sessile as adults and range in size from 1 cm to 2 m across (Figure 8 (a)). Most sponges are hermaphrodites releasing sperm to surrounding water. Their eggs remain in their bodies and fertilized by other sperm drawn in with water. The fertilized eggs develop into ciliated larvae swimming or crawl looking for suitable locations to rest and grow. Most sponges are marine and more than 100 freshwater species. Freshwater ones are often mistaken for plants as they have symbiotic blue–green algae, or cyanobacteria. Marine sponges can be very abundant, and are important as foods and shelters for many organisms (large sponges can harbour thousands of shrimp). Sponges are commercially valuable and are threatened by overharvesting in some regions. The Cnidaria has nearly 9000 species of hydras, anemones, jellyfish, and coral animals (Figure 8(b) and (c)) and don't have mesoderms and exhibit radial symmetries, and are the simplest animals with specialized nerve, muscle, digestive, and reproductive tissues. They all have tentacles with stinging cells containing nematocysts, capsules containing a barbed, thread-like tube delivering a paralyzing sting when propelled into targets.
nematocyst is a capsule in specialized cells of cnidarians with toxins that can be propelled to targets, causing paralyzation (called a stinging cell)
Porifera
Porifera
Sponges are part of the phylum in the taxonomic rank. Sponges have unspecialized cells that can transform into other types and that often migrate between the main cell layers and the mesohyl in the process. Sponges don't have complex nerves.
They're multicellular organisms with bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells.
Sponges were the first to branch off evolutionary tree from the last common ancestor of all animals, making them sister group of all other animals.
Sponges have unspecialized cells that can transform into other types and that often migrate between the main cell layers and the mesohyl in the process.
Sponges don't have complex nervous systems, digestive or circulatory systems like humans. Instead, most rely on maintaining constant water flow through bodies for food and oxygen and to remove wastes.
Coral animals are cnidarians producing external skeletons made of calcium carbonate, which accumulate overtime. These form complex structures and give habitat for countless of other marine species. They're deemed the most biologically diverse of aquatic ecosystems (Figure 9). Though the status of many cnidarians is unknown, 236 species are deemed at risk, mostly due to pollution and habitat destruction. The greenhouse gases effects and climate change on water chemistry may be a greater issue. Most of the world’s today coral reefs are highly threatened.
Figure 9. Communities of coral animals can build complex reefs that are home to many other species.
Protostome invertebrates
Protostome invertebrates
The protostome invertebrates has 6 major animal phyla and most of all animal species, occupying most environment and are mostly very abundant.
Body plans and life cycles
Body plans and life cycles
Protostomes' body plans and life cycles are highly diverse.
Figure 10 shows a representative body plan from the most biologically successful class of organisms—Phylum Arthropoda, Class Insecta.
Figure 10 There are more known species of insects than of any other class of organisms on Earth. Their success is due in large part to an effi cient body plan that includes nervous, digestive, respiratory, excretory systems and reproductive systems; advanced sensory structures; and the ability to fly.
Other characteristic body features of protostomes have powerful claws of crabs and lobsters, tentacles, snail and clam ornate shells, and butterfly wings. Many, like insects, have a life cycle with a number of distinct larval stages. These life cycles have larval stages that are sometimes unrecognizable when compared to an adult. Figure 11 shows examples of four larvae.
Figure 12 Tomato hornworms are common pests in Ontario. These caterpillars feed on tomato plants, including the fruit.
Human-Protostome interactions
Human-Protostome interactions
Many protostomes compete with humans for food. Insects are one of the best known. Mostly all food crop have important insect pests (like Ontario important pests corn crops has about 13 different insect species of insect and a slug species (Phylum Mollusca) (Figure 12). Food losses due to them are significant, and the cost of controlling them are a major factor in food production cost. Most crops are planted in large monocultures. This and insects' ability to reproduce quickly, grow their populations quickly. Pesticides keep pest populations in check, but some became resistant. But pesticides also damage the environment and harm humans. Organic and alternative farming methods reduce synthetic pesticides uses. They rely instead on natural predatory insects to control pests.
Pathogen and vectors
Pathogen and vectors
Humans suffer from many parasitic diseases. Some caused by protists, some by animals—particularly nematodes, tapeworms, and flukes species. Nematode parasites are capable of infecting many body tissues. Adult tapeworms inhabit intestines and pass their fertilized eggs out with feces (Figure 13). Parasitic flukes often live in lungs or blood vessels. One blood fluke that normally infects waterfowl is responsible for “swimmer’s itch.” Many biting animals are vectors, spreading disease. Like mosquitoes spread malaria, yellow fever, and West Nile virus from person to person. Ticks and fleas spread Lyme disease and the plague. Controlling these disease spreads involves controlling the animal vectors.
Figure 13 (a) A tapeworm has a specialized head, or scolex. (b) Some tapeworms have heads with barbs and suckers for attaching to the wall of the intestine.
Food and economic benefits
Food and economic benefits
Many protostomes benefit humans. Many of these are eaten (mollusks; clams and scallops, crustaceans like shrimp and lobsters, and honey by bees).
We use oysters for food and as a source of Pearls (Figure 14). Coral reefs are used in some countries as mineral sources for cement production.
Deuterostomes
Deuterostomes
Deuterostomes are less diverse but much more familiar collection of animals. This animal branch phylogenetic tree has 2 main groups:
echinoderms (starfish, sea urchins, sea cucumbers, close relatives)
and chordates (vertebrates and their closest relatives).
Echinoderms
Echinoderms
The 6500 echinoderms species are the only invertebrates exhibiting the same pattern of early embryonic development as vertebrates. Their immature stages are free swimming and bilaterally symmetrical. As they grow, they develop a radially symmetrical pattern around 5+ arms (Figure 15(a)).
Figure 15 (a) Echinoderms like this brittle star are bilaterally symmetrical as larvae but radially symmetrical as adults.
(b) Echinoderms move using a system of water-filled canals that control their arms and tube feet.
Adult echinoderms have unique body plans, with a complete digestive system, a simple circulatory system, and no respiratory, excretory system, nor a head region. Their nervous system circles the mouth and extends into the arms. Echinoderms move using a water-filled vascular system using the principles of hydraulics. By pumping water with muscle action and opening and closing valves within the system, echinoderms can control the movements of their arms and tube feet (Figure 15(b)). This also allows them to create considerable force easily. Some starfish do this to open and devour large clams.
Chordates
Chordates
Chordates are fish, amphibians, mammals, reptiles, and birds. Though birds are put here as a separate class, they're now deemed a recently evolved reptile groups. They include the most complex living beings. They may have evolved from bilaterally symmetrical ancestors with segmented bodies, which had gill slits, a dorsal nerve cord, and a flexible rod called a notochord. The notochord was an anchor for attaching the body wall muscles (Figure 16), which may have enhanced their movements. Primitive and many modern chordates the gill slits are used for filter feeding. Many other crucial features evolved, like vertebrae, paired appendages, a bony skeleton, and more evolved brain and sensory systems. Internal supporting skeletons enabled chordates to develop large body sizes—most are much larger than most invertebrates.
Figure 16 These are the distinguishing features of all chordates' ancestors. The simplest living chordates still retain this body form.
Blue whales, and vertebrates, are deemed to be the largest animals to exist. A key development that enabled some of the vertebrates to conquer land was the evolution of a waterproof amniotic egg. An amniotic egg has gained membranes and an outer shell making it resistant to water loss. Mammals, like humans retain amniotic membranes around the developing fetus. Only a few species of mammals, like the platypus and the echidna, still lay shelled eggs.
amniotic egg an egg with an outer leathery or hard shell and specialized internal membranes that protect and nourish the embryo
Cephalization
Cephalization
Cephalization is when the nervous system is focused on a head region (head, mouth, nose...).
Tripoblastic
Tripoblastic
Tripoblastic animals have 3 germ layers and are often categorized as either protostome or deuterostomes.
Prostomes = often first embryonic opening (blastopore) develops into the mouth and a second one forms into the anus
If deuterostome then = first instead becomes an anus and the second becomes the mouth
Germ layers eventually develop into structures of the organism: the ectoderm, mesoderm, and endoderm.
Most tripoblastics have a coelom; either a true coelom, a body cavity derived from the mesoderm, filled with fluid and act as a space for organs, providing shock absorption and space for organ development,
or a fake coelom (pseudocoelom) Animals are classified on whether they have a true, false, or no coelom.
3. Phylum platyhelminthes are "flat"worms ("plat" rimes with "flat"), mostly are aquatics, some terrestrials fresh water or saltwater. They include planarian and tapeworm, many are parasitic
4. Phylum nematoda (pinworm, hookworms) have big ecological impact, infesting crops, and parasitics to many animals. Some are largely used in study and useful for soil ecology.
9 major phyla
9 major phyla
Phylum porifera (Most adults are sessile) are aquatic sponges with porous bodies, letting water and food to pass through. They have special cells doing intracellular digestion; digestion inside the cells, thus they don't have organs no tissue. They have no symmetry.
sessile: motionless
Phylum Cnidaria are jellies and hydras with a gut opening that's both the mouth and anus, and intracellular digestion and extracellular digestion cells; outside of their cells in a gastrovascular cavity. Most have radial symmetry and no cephalization and coelom. They have often 2 forms:
Medusa and polyp, specialized cells with organelles used to sting preys.
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Fisheries in Peril
Many animals (oysters, squid, sea cucumbers, fish, shrimps) are harvested from natural populations and some are farmed in cages or other engineered structures. Tragically many believe that more than 50% of major fisheries are at declines. Many kind of fisheries are at risk, like wild tuna and salmon Antlantic cod, and shark species.
Issue
Issue
2 largest groups of animals are Invertebrates and vertebrates
Vertebrates have spines/backbones
Invertebrates don't have spines
Invertebrate
Invertebrate
Most animals are invertebrates, such as
star fish, arachnids, jellyfish, insects, lobsters or clams
On land most animals are small like insects, unlike in water that are much biggers
Invertebrates come in all different shapes and sizes. Some can be seen only through a microscope. But the giant squid is an invertebrate, and it can grow to a length of 65 feet (20 meters).
They're grouped according to features.
Many such as worms, have soft bodies.
Corals, jellyfish, and sea anemones are invertebrates that have stinging tentacles.
Mollusks have soft bodies as well, but most also have a thick outside shell.
Oysters and snails are mollusks. Squid and octopuses are also mollusks even though they do not have shells.
Crustaceans
Crustaceans
Belongs to invertebrates
Vertebrate
Vertebrate
Vertebrates on the other hands makes less than 5% of all species on Earth, such as reptiles, fishes, mammals, birds and amphibians.
Fish
Fish
Characteristics of fishes:
Lives and breath underwater
Use gills instead of lungs to breath/get oxygens
Cold-blooded animals, meaning that they can't control their blood temperature which changes depending on the environment
Most lay eggs
Amphibian
Amphibian
Animals that can live on both land and water. They includes:
frogs, crocodiles, toads, salamenders, newts.
Most have smooth and moist skin. When their eggs hatch, babies may not look like parents such as frogs and lizards, since some must go through metamorphosis to become adult.
Reptiles
Reptiles
Animals that can live on both land and water. They includes:
frogs, crocodiles, toads, salamenders, newts.
Most have smooth and moist skin. When their eggs hatch, babies may not look like parents such as frogs and lizards, since some must go through metamorphosis to become adult.
Primate
Primate
A type of group of mammals including some of the most smartest animals and most of them are monkeys a
The major kinds of are: humans, apes, monkeys, tarsiers, lemurs, and lorises. There are more than 300 species, or types, of primates.
sThese different types have many physical features in common and for this reason scientists believe that they may share a common ancestor.
Most of them have thumbs that can bend to meet other fingers, allowing him to grab, flat nails on fingers like humans.
Since most are monkeys, they are omnivore as they eat various foods: fruits, flowers, leaves, birds’ eggs, insects, and other small animals.
Deep emotional bonds can often develop between mother and child.
Aside from humans all of them have big toes that can bend and grip.
Over course of life, female primates tend to have fewer young than other animals do. Most primates give birth to one baby at a time.
Babies take a long time to grow into adults. Primates must take care of their young for much longer than other animals do.
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