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Topic 5.5
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Linnaeus introduced a system of naming and
classifying species in the 18th century.
Linnaeus’s system assigns to each species a twopart latinized name, or binomial.
The first part of a binomial is the genus to which a
species belongs.
The second part identifies one species within that
genus.
The two parts must be used together to name a
species.
For example, the scientific name for the domestic
cat is Felis catus.
◦ Notice that the first letter of the genus name is capitalized
and that the binomial is italicized and latinized.
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Linnaeus also grouped species into a
hierarchy of categories.
Beyond the grouping of species within
genera, the Linnaean system extends to
progressively broader categories of
classification.
It places similar genera in the same family,
puts families into orders, orders into classes,
classes into phyla, phyla into kingdoms, and
kingdoms into domains.
◦ Did King Phillip Come Over From Great Spain?
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Taxonomy is the grouping of organism into
more inclusive categories.
◦ Each taxonomic unit at any level—family Felidae or
class Mammalia—is called a taxon.
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Phylogenetic trees are used to depict
hypotheses about the evolutionary history of
species.
◦ These branching diagrams reflect the hierarchical
classification of groups nested within more inclusive
groups.
◦ The “highest” or most inclusive taxon is at the
bottom, and each branch point represents the
divergence of two lineages from a common ancestor.
Phylogenetic Tree
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Cladistics involves the identification of clades,
evolutionary branches that consist of an
ancestral species and all its descendants.
 Based on the Darwinian concept that evolution
proceeds when a new heritable trait develops in an
organism and is passed on to its descendants.
 Groups of organisms that share such a new, or
derived, trait are more closely related to each other
than to groups that have only the original set of traits.
 The new traits are called shared derived characters,
while the original traits present in ancestral groups
are called shared primitive characters.
 A cladogram is a diagram used to depict the pattern
of shared characters.
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A dichotomous key is a tool that allows the
user to determine the identity of items in the
natural world, such as trees, wildflowers,
mammals, reptiles, rocks, and fish.
◦ Keys consist of a series of choices that lead the user
to the correct name of a given item.
◦ "Dichotomous" means "divided into two parts".
◦ Therefore, dichotomous keys always give two
choices in each step.
Dichotomous Key
Nonvascular Plants:
Approximately 475million years ago, plants originated from
an aquatic green algal ancestor.
◦ Early diversification gave rise to what are called the
bryophytes: liverworts, hornworts, and mosses.
◦ Bryophytes resemble other plants in having retained on the
parent plant.
◦ Unlike other plants, however, bryophytes lack vascular tissue
and are therefore called “nonvascular plants”
◦ Without strong cell walls of vascular tissue, bryophytes lack
support.
◦ Thus, a mat of moss actually consists of many plants growing
in a tight pack, holding one another up.
◦ The mat is spongy and retains water.
◦ The flagellated sperm of mosses and other bryophytes swim
to the eggs, so fertilization requires the plant to be covered
with a film of water.
Hornwort
Mosses
Liverwort
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Vascular Plants
◦ Originated about 420 million years ago.
◦ Their lignin-hardened vascular tissues provide strong
support, enabling stems to stand upright and grow tall on
land.
◦ Two clades of vascular plants are informally called seedless
vascular plants:
 Lycophytes (club mosses) and wide-spread pterophytes
(ferns and their relatives)
 A fern has well-developed roots and rigid stems.
 In many species, the leaves, commonly called fronds,
sprout from stems that grow along the ground.
 Ferns are common in temperate forests, but they are most
diverse in tropics.
 Ferns have flagellated sperm that require a layer of water to
reach the eggs, and they have spores enclosed in tough,
protective walls.
Club Mosses
Ferns
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Vascular plants
◦ Vascular plants with seeds, seed plants, evolved about 360
million years ago.
◦ A seed consists of an embryo packaged with a food supply
with a protective covering.
◦ Today, seed plants account for over 90% of the approximately
290,000 species of living plants.
◦ Several key adaptations underlie the enormous success of
seed plants:
 Seeds are survival packets for life on land, contributing to
the spread of plants to diverse habitats by allowing plant
embryos to be dispersed more widely.
 Seeds do not require a water layer for fertilization. They
produce pollen, which transfers sperm to egg producing
parts of the plant. Pollen is carried passively by wind or
animals.
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Vascular Plants
◦ Seed Plants: Gymnosperms and Angiosperms
 Gymnosperms are among the earliest seed plants.
 “naked” seed; seeds are said to be naked because they are
not produced in specialized chambers.
 The largest clade of gymnosperms are the conifers,
consisting mainly of cone-bearing trees, such as pine,
spruce, and fir.
 Angiosperms are the flowering plants, which appeared
at least 140 million years ago.
 Flowers are complex reproductive structures that develop
seeds within protective chambers.
 The great majority of living plants—some 250,000 species–
are angiosperms and include a wide variety of plants, such
as grasses, flowering shrubs, and flowering trees.
Angiosperm
Gymnosperm
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Four key adaptations for life on land
distinguish the main lineages of the plant
kingdom:
◦ 1. Dependent embryos are present in all plants
◦ 2. Lignified vascular tissues mark a lineage that gave
rise to most living plants.
◦ 3. Seeds are found in a lineage that includes all living
gymnosperms and angiosperms and that dominates
the plant kingdom today.
◦ 3. Flowers mark the angiosperm lineage.
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One way that biologist categorize the
diversity of animals is by certain general
features of body structure, which together
describe what is referred to as an animal’s
“body plan.” These distinctions are used to
help infer the phylogenetic relationships
between animal groups.
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Symmetry
◦ Radial symmetry
 For example, a sea anemone; the body parts radiate from
the center.
 Any imaginary slice through the central axis divides a
radially symmetrical animal into mirror images. Thus, the
animal has a top and a bottom, but not right and left sides
 These animals are typically sedentary or passively drifting,
meeting its environment equally on all sides.
◦ Bilateral symmetry
 For example, a lobster; has mirror-image right and left
sides; a distinct head, or anterior, end; a tail, or posterior
end; a back, or dorsal, surface; and a bottom, or ventral,
surface.
 The brain, sense organs, and mouth are usually located in
the head.
 These animals are usually active and travel headfirst
through the environment, with their eyes and other sense
organs contacting the environment first.
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Body plans also vary in the organization of tissues.
◦ True tissues are collections of specialized cells, usually
isolated from other tissues by membrane layers, that
perform specific functions.
 Some animals have no tissues (sponge);
 In some animals, cell layers formed during gastrulation
give rise to true tissues and to organs:
 Some animals have only two layers, an ectoderm and
endoderm; most animals have three layers, including a
mesoderm.
Body plans also vary in the organization of tissues.
(continued…)
◦ Animals with three tissue layers may be characterized by the
presence or absence of a body cavity.
 This fluid-filled space between the digestive tract and
body wall cushions the internal organs and enables them
to grow and move independently.
 In soft-bodied animals, a noncompressible fluid in the
body cavity forms a hydrostatic skeleton that provides a
rigid structure against which muscles contract, moving the
animal.
 A roundworm has a body cavity called a pseudocoelom
 “False hollow”; not completely lined by tissue derived from
mesoderm.
 A segmented worm has a body cavity called a true coelom,
which is completely lined by tissue derived from
mesoderm.
Acoelomate
(Flatworm)
Pseudocoelemate
(roundworm)
Coelomate
(Segmented
worm)
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Animals with three tissue layers can be
separated into two groups based on details of
their embryonic development,
◦ Such as the fate of the opening formed during
gastrulation that leads to the developing digestive
tract.
 In protostomes, this opening becomes the mouth.
 In deuterostomes, this opening becomes the anus, and
the mouth forms from a second opening.
 Other differences between protostomes and
deutorostomes include the pattern of early cell
divisions and the way the coelom forms.
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Phylum Porifera
Stationary animals that are so sedentary that the ancient Greeks
believed them to be plants.
Majority of the species are marine, although some are found in
freshwater.
A simple sponge resembles a thick-walled sac perforated with holes.
◦ Water is drawn through the pores into a central cavity, then flows
out through a larger opening.
◦ More complex sponges have branching water canals.
They are suspension feeders, also known as filter feeders, animals
that collect food particles from water passed through some type of
food-trapping equipment.
◦ To obtain enough food to grow by 100 g (about 3 ounces), a
sponge must filter 1,000 kg (about 275 gallons) of sea water.
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Adult sponges are sessile, meaning they are anchored in place;
therefore they cannot escape from predators.
◦ Researchers have found that sponges produce defensive
compounds such as toxins and antibiotics that deter
pathogens, parasites, and predators.
◦ Some of these compounds may prove useful to humans as
new drugs.
◦ Also, as sponges trap particles, they perform an important
ecological service by purifying the water around them.
They are the simplest of all animals.
◦ They have no nerves or muscles, though their individual cells
can sense and react to changes in the environment.
◦ Since the cell layers are loose federations of cells, they are
not considered true tissues.
◦ Biologist hypothesize that the sponge lineage arose very
early from the multicellular organisms that gave rise to the
animal kingdom.
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Bilateral symmetry
Phylum Platyhelminthes
Thin, simple, ribbonlike animals range in length from about 1
mm to 20 m and live in marine, freshwater, and damp terrestrial
habitats.
In addition to free-living forms, there are many parasitic species.
Most flatworms have a gastrovascular cavity with one opening.
The fine branches of the gastrovascular cavity distribute food
throughout the animal.
Three major groups of flatworms include:
◦ Planarians, or free-living flatworms
◦ Flukes, or parasitic flatworms
◦ Tapeworms, or parasitic flatworms
Planaria
Fluke
Tapeworm
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Phylum Mollusca
Snails, slugs, oysters, clams, octopuses, and squids
Soft-bodied, protected with a hard shell.
Basic body plan consists of three main parts:
◦ A muscular foot
 Functions in locomotion
◦ A visceral mass
 Containing most of the internal organs
◦ A mantle
 A fold of tissue that drapes over the visceral mass and
secretes a shell in clams and snails.
 Also produces a water-filled chamber called the mantle
cavity , which houses the gills.
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Most molluscs also have a unique rasping organ called a radula,
which is used to scrape up food.
Most molluscs have separate sexes, with reproductive organs
located in the visceral mass.
◦ Have a ciliated larval stage called a trocophore.
Have a true coelom and circulatory system—an organ system
that pumps blood and distributes nutrients and oxygen
throughout the body.
Three diverse groups:
◦ Gastropods
 Including snails and slugs
◦ Bivalves
 Including clams, scallops, and oysters
◦ Cephalopods
 Including squid and octopuses
Snail
Clam
Octopus
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Phylum Annelida
Have segmentation, the subdivision of the body along its length
into a series of repeated parts (segments), played a crucial role
in the evolution of many complex animals.
◦ A segmented body allows for greater flexibility and mobility,
and it probably evolved as an adaptation facilitating
movement.
◦ An earthworm, a typical annelid, uses its flexible, segmented
body to crawl and burrow rapidly into the soil.
Annelids range in length from 1 mm to 3m, the length of some
giant Australian earthworms.
They are found in damp soil, in the sea, and in most freshwater
habitats.
Some aquatic annelids swim in pursuit of food, but most are
bottom-dwelling scavengers that burrow in sand and mud.
There are three main groups of annelids:
◦ Earthworms
◦ Polychaetes
◦ Leeches
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Earthworms and their relatives
◦ The coelom is partitioned by membrane walls.
◦ Many of the internal body structures are repeated within
each segment
◦ The nervous system includes a simple brain and a ventral
nerve cord with a cluster of nerve cells in each segment.
◦ The excretory organs which dispose of fluid waste, are also
repeated in each segment.
◦ The digestive tract, is not segment; it passes through the
segment walls from the mouth to the anus.
◦ Have a closed circulatory system, in which blood remains
enclosed in vessels as it distributes nutrients and oxygen
throughout the body.
 The pumping organ, or “heart” is simply an enlarged region of
the dorsal blood vessel plus five pairs of segmental vessels near
the anterior end “aortic arches”
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Earthworms and their relatives (continued)…
◦ Each segment is surrounded by longitudinal and circular
muscles.
 They move by coordinating contraction of these two sets of
muscles.
 These muscles work against the coelomic fluid in each
segment.
 Each segment also has four pairs of stiff bristles that
provide traction for burrowing.
◦ They are hermaphodites
 They have both male and female reproductive structures.
 They mate and cross-fertilize by exchanging sperm.
 A specialized thickened region of the worm, called the
clitellum, secretes a cocoon made of mucus.
 The cocoon slides along the worm, picking up the eggs and
the received sperm.
 The cocoon slips off the worm into the soil, where the
embryos develop.
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Earthworms and their relatives (continued)…
◦ Earthworms eat their way through soil, extracting
nutrients as soil passes through their digestive
tube.
◦ Undigested material, mixed with mucus secreted
into the digestive tract, is eliminated as feces
though the anus.
◦ Farmers value earthworms because they aerate
tehsoil and their feces improve the soil’s texture.
Earthworm anatomy
Earthworm
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Polychaetes
◦ Sandworm, which lives on the sea floor
◦ Each segment has a fleshy, paddle-like appendages with many
stiff bristles that help the worm wriggle about in search of small
invertebrates to eat.
Leeches
◦ Notorious for their blood sucking habits.
◦ The majority inhabit fresh water, but there are also marine
species and a few terrestrial
◦ Range in length from 1 to 30 cm.
◦ Use razor-like jaws to slit the skin of an animal.
 Host is usually oblivious to this attack because the leech
secretes an aesthetic as well as an anticoagulant into the
wound.
 Then the leech sucks as much blood as it can hold, often more
than ten times its own weight.
Polychaete
Leech
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Phylum Arthropoda
Includes crayfish, lobsters, crabs, barnacles,
spiders, ticks, and insects
2/3 of all animals are arthropods; estimated
1018 individuals.
Segmented, have a hard exoskeleton, and
jointed appendages.
The appendages are variously adapted for
sensory reception, defense, feeding, walking,
and swimming.
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The exoskeleton, which covers the body and
appendages, is an external skeleton that
protects the animal and provides points of
attachment for the muscles that move the
appendages.
◦ Nonliving covering, or cuticle, is constructed from
layers of protein and chitin, a polysaccharide.
◦ Thick around the head, where its main function is to
house and protect the brain.
◦ It is paper-thin and flexible in other locations, such
as the joints of the legs.
◦ As it grows, an arthropod must periodically shed its
old exoskeleton and secrete a larger one, a complex
process called molting.
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Body of most arthropods is formed of several
distinct groups of segments: the head, thorax,
and abdomen.
◦ Head bears sensory antennae, eyes, and jointed
mouthparts on the ventral side.
◦ The thorax bears a pair of defensive appendages
(the pincers) and four pairs of legs for walking.
◦ The abdomen has swimming appendages.
◦ *in some arthropods, the head and thorax are partly
fused into a region called the cephalothorax.
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Have an open circulatory system in which a
tube-like heart pumps blood through short
arteries into spaces surrounding the organs.
Most species have gills.
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Arthropod groups:
◦ Chelicerates
 Includes horseshoe crabs, arachnids (scorpions, spiders,
ticks, and mites)
◦ Millipedes and centipedes
◦ Crustaceans
 Lobsters and crayfish
Horse shoe crab
Spider
Lobster