Download Ch. 18 The Evolution of Animal Diversity (Lecture Notes)

AP Biology CMR Unit 6 Ch. 18 Evolution of Animal Diversity @ SOHI ‘99
Unit 6
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The Evolution of Animal Diversity - Chapter 18
University of Minnesota.
Department of Ecology, Evolution, and Behavior.
URL: http://biosci.cbs.umn.edu/class/biol/1106/
General Zoology (BIOL 1106)
Note-Taking Hints
At the beginning of the course and periodically throughout the quarter, review the following list of major systems. When
you are taking notes in lecture, when reading the textbooks, and during lab make sure you have filled in information about
all of the following. If a certain system is absent or reduced, and therefore only briefly covered, then record that in your
notes. Then, when reviewing for quizzes or exams, use the facts recorded for each of these systems in each of the major
Phyla or Classes in making a detailed study outline and/or flashcards. Or make a Phylum Review Table
Biology 1106 Guide to Major Systems and Concepts:
Phylum:
Taxonomic Classes:
Examples (common names) from Lab or Lecture:
Etymology (origin of the word) or other "name games" to help you remember the above:
Body Plan (Symmetry etc...):
Body Wall:
Feeding, Digestion:
Circulation:
Excretion:
Respiration:
Nervous System:
Arrangement:
Sense Organs:
Muscles & Locomotion:
Reproduction:
Morphology:
Asexual, Sexual or Both?
Monoecious (hermaphroditic) or Dioecious?
Other Interesting Behaviors:
Phylogeny:
Happy note taking, don't cramp your hand or you won't do well on the dissections!!!!!!!
For more on Outline Methods, go to the Animal World at a Glance Page.
For more details, go to the Zoological Concepts Page.
For more on how to use the Phylum and Class Pages, go to the Phyla Index Page.
For another review technique, go to the Phyla Comparison Page.
Go to the Zoology Home Page.
Tree of Life
http://phylogeny.arizona.edu/tree/
AP Biology CMR Unit 6 Ch. 18 Evolution of Animal Diversity @ SOHI ‘99
Overview of all Phyla
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I. Kingdom Protista
Subkingdom Protozoa- the single celled "animals"
1. Phylum Sarcomastigophora
a. Subphylum Sarcodina-the amebas (Amoeba)
b. Subphylum Mastigophora-the flagellates (Euglena)
2. Phylum Ciliophora- the ciliates (Paramecium)
3. Phylum Apicomplexa- (Plasmodium)
II. Kingdom Animalia
A. Phylum Porifera- the sponges
B. Phylum Cnidaria
1. Class Hydrozoa- (Hydra, Obelia)
2. Class Syphozoa- the true jellyfish (Aurelia)
3. Class Anthozoa- the "flower" animals (sea anenome, corals)
C. Phylum Platyhelminthes- the flat "worms"
1. Class Turbellaria- (Planaria)
2. Class Cestoda- (tapeworms)
3. Class Trematoda- (flukes)
D. Phylum Nematoda- the round "worms"- (Ascaris)
E. Phylum Mollusca
1. Class Bivalvia- "two valves"- (clams, mussels)
2. Class Gastropoda- "stomach foot- (snails, slugs)
3. Class Cephalopoda- "head foot"- (squid, octopus, nautilus)
F. Phylum Annelida- the segmented worms
1. Class Polychaeta-"many hairs"- (clamworms)
2. Class Oligochaeta- "few hairs"- (earthworms)
3. Class Hirudinea- (leeches)
G. Phylum Arthropoda
1. Subphylum Chelicerataa. Class Meristomata-"thigh mouth" (horseshoe crab)
b. Class Arachnida-(spiders, ticks, scorpions)
2. Subphylum Crustacea-(lobster, shrimp, crab, crayfish)
3. Subphylum Uniramiaa. Class Diplopoda-"2 feet"- (millipedes)
b. Class Chilopoda-" "- (centipedes)
c. Class Insecta- (butterflies, ants, crickets, roaches)
*You may need to know some insect Orders.
H. Phylum Echinodermata- "spine skin"
1. Class Asteroidea- (sea stars)
2. Class Ophiuroidea- (brittle stars)
3. Class Holothuroidea- (sea cucumbers)
4. Class Echinoidea- (sea urchins, sand dollars)
5. Class Crinoidea- (sea lilies, feather stars)
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AP Biology CMR Unit 6 Ch. 18 Evolution of Animal Diversity @ SOHI ‘99
Overview of all Phyla
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I. Phylum Chordata1. Subphylum Urochordata- "tail cord"- (tunicates)
2. Subphylum Cephalochordata- "head cord"- (Amphioxus)
3. Subphylum Vertebrata- "backboned"
a. Superclass Aganatha- "without jaws"- (lamprey)
b. Superclass Gnathostomata- "jawed mouth"
1. Class Chondrichthyes
-the cartilaginous "fish"- (sharks, rays)
2. Class Osteichthyes
-the bony fish- (perch)
3. Class Amphibia
-Orders: Anura, Caudata, Gymnophiona
4. Class Reptilia
-Orders:Squamata, Testudines, Crocodilia
5. Class Aves
-Orders: Lots!, see Class Page
6. Class Mammalia
-Orders: Lots!, see Class Page
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Phylum Porifera The Sponges
"Sponges are the simplest multicellular animals. Because the cell is the elementary unit of life, the evolution of organisms
larger than unicellular protozoa arose as an aggregate of such building units. There are many advantages to multicellularity
as opposed to simply increasing the mass of a single cell. Since it is at cell surfaces that exchange takes place, dividing a
mass into smaller units greatly increases the surface area available for metabolic activities. Thus multicellularity is a highly
adaptive path toward increasing body size."
Major Characteristics of Phylum Porifera
1 Multicellular; body a loose aggregation of cells of mesenchymal origin;
2 Body with pores (ostia), canals, and chambers that serve for passage of water;
3 All aquatic; mostly marine;
4 Symmetry radial or none;
5 Epidermis of flat pinacocytes; most interior surfaces lined with flagellated collar cells (choanocytes) that create water
currents; a gelatinous protein matrix called mesoglea contains amebocytes, collencytes, and skeletal elements;
6 Skeletal structure of fibrillar collagen (a protein) and calcareous or siliceous crystalline spicules, often
ombined with variously modified collagen (spongin) fibrils;
7 No organs or true tissues; digestion intracellular; excretion and respiration by diffusion;
8 Reactions to stimuli apparently local and independent; nervous system probably absent;
9 All adults sessile and attached to substratum;
10 Asexual reproduction by buds or gemmules and sexual reproduction by eggs and sperm; freeswimming ciliated larvae.
Sponges are differentiated by the type of canal system
Asconoids - Small and tube shaped. Water enters through microscopic dermal pores into a large cavity called the
spongocoel, which is lined with choanocytes. The choanocyte flagella pull the water through the pores and expel it through
the single osculum.
Syconoids - Syconoid sponges also have a tubular body and single osculum, but the body wall is thicker and more
complex. Water enters through incurrent canals that deliver it to radial canals, which are lined with choanocytes. The radial
canals then empty into the spongocoel, which is lined with epithelial cells and not with choanocytes.
Leuconoids - Leuconoid sponges have the most complexity and are the best adapted for increase in sponge size. Most
leuconoids form large colonial masses, each member of the mass having its own osculum, but individual members are
poorly defined and often impossible to distinguish. Clusters of flagellated chambers are filled from incurrent canals and
discharge water into excurrent canals that eventually lead to the osculum.
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Phylum Cnidaria
"... many cnidarians are very effective predators that are able to kill and eat prey much more highly organized, swift, and
intelligent. They manage these feats because they possess tentacles bristling with tiny, remarkably sophisticated weapons
called nematocysts.
A nematocyst is secreted within the cell that contains it. As it is secreted, it is endowed with the potential energy to power
its discharge. Achieving a velocity of 2 m/sec, it instantly penetrates its prey and injects a paralyzing toxin."
Major Characteristics of Phylum Cnidaria
1 Entirely aquatic; some in fresh water but mostly marine;
2 Radial symmetry or biradial symmetry around a longitudinal axis with oral and aboral ends; no definite head;
3 Two basic body forms: polyp and medusa;
4 Exoskeleton or endoskeleton of chitinous, calcareous, or protein components in some;
5 Body with two layers, epidermis and gastrodermis; with mesoglea (diploblastic); mesoglea with cells and connective
tissue in some (triploblastic);
6 Gastrovascular cavity or coelenteron (often branched or divided with septa) with a single opening that serves as both
mouth and anus; extensible tentacles usually encircling the mouth or oral region;
7 Special stinging cell organelles called nematocysts in either or both epidermis and gastrodermis;
nematocysts abundant on tentacles, where they may form batteries or rings;
8 Nerve net with symmetrical and asymmetrical synapses; some sensory organs; diffuse conduction;
9 Muscular system (epitheliomuscular type) of an outer layer of longitudinal fibers at base of epidermis and an inner one of
circular fibers at base of gastrodermis; modifications of this plan in anthozoans, such as separate bundles of
independent fibers in the mesoglea;
10 Reproduction by asexual budding (in polyps) or sexual reproduction by gametes (in all medusae and some polyps;
sexual forms monoecious or dioecious; planula larva; holoblastic cleavage;
11 No excretory or respiratory systems
12 No coelomic cavity
Classes of Cnidarians:
Class Hydrozoa - Most hydrozoans are marine and colonial in form, and typically include both the medusa and polyp stage
in their life cycle. Some, however, have no medusa stage, and some occur only as medusae and have no polyp
stage.
Examples: Hydra, Obelia
Class Scyphozoa - Class Scyphozoa includes most of the larger "jellyfishes". A few, such as Cyanea, may attain a bell
diameter exceeding 2 m and tentacles 60 to 70 m long, but most range from 2 cm to 40 cm in diameter. Their
polyp stage is absent or greatly reduced, and the medusae of this class have no velum.
Examples: Aurelia, Cyanea
Class Anthozoa - Anthozoa means "flower animal," and anthozoans are indeed polyps with a flowery
appearance. They do not have a medusa stage. Anthozoans are all marine and are found all over the world, in
various sizes and habitats.
Examples: Sea anemones, corals
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Phylum Platyhelminthes The Flat "Worms"
"... if an animal is active in seeking food, shelter, home sites, and reproductive mates, it requires a different set of strategies
[than the radiate animals] and a new body organization.
The ... acoelomate phyla considered [here] are not greatly advanced in organization over the Radiata except in symmetry.
The evolutionary consequence of that advancement alone was enormous, however, for it is the type of symmetry assumed
by all more complex animals."
Major Characteristics of Phylum Platyhelminthes
1 Three germ layers (triploblastic);
2 Bilateral symmetry; definite polarity of anterior and posterior ends;
3 Body flattened dorsoventrally in most; oral and genital apertures mostly on ventral surface;
4 Body with multiple reproductive units in one class (Cestoda);
5 Epidermis may be cellular or syncytial (ciliated in some);
6 Muscular system of mesodermal origin, in the form of a sheath of circular, longitudinal, and oblique layers beneath the
epidermis or tegument;
7 No internal body space (acoelomate) other than digestive tube; spaces between organs filled with
parenchyma;
8 Digestive system incomplete (gastrovascular type), absent in some;
9 Nervous system consisting of a pair of anterior ganglia with longitudinal nerve cords connected by
transverse nerves and located in the parenchyma in most forms; similar to cnidarians in forms with more primitive
characters;
10 Simple sense organs, eyespots in some;
11 Excretory system of two lateral canals with branches bearing flame cells (protonephridia), lacking in some forms;
12 Respiratory, circulatory, and skeletal systems lacking;
13 Most forms monoecious; reproductive system complex, usually with well-developed gonads, ducts, and
accessory organs; internal fertilization; life cycle simple in free-swimming forms and those with single hosts;
complicated life cycle often involving several hosts in many internal parasites;
14 Class Turbellaria mostly free-living; classes Trematoda and Cestoda entirely parasitic.
Classes of flat "worms":
Class Turbellaria - Turbellarians are mostly free-living worms than range in length from 5 mm or less to 50 cm. Usually
covered with ciliated epidermis, they are typically creeping worms that combine muscular with ciliary movement
to achieve locomotion. The mouth is on the ventral side.
Example: Dugesia
Class Trematoda - The trematodes are all parasitic flukes, and as adults they are almost all found as
internal parasites of vertebrates.
Examples: Clonorchis, Schistosoma
Class Cestoda - The cestodes, or tapeworms, usually have long flat bodies made up of many
reproductive units (proglottids) and have no digestive system. They also have a specialized
structure called the scolex ("holdfast") which is the organ by which they attach to their host. It is
usually provided with suckers and often with hooks or spiny tentacles.
Examples: Taenia
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Phylum Nematoda
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The Round "Worms"
"Nematodes are abundant over most of the world, yet most people are only occasionally aware of them as parasites of
humans or of their pets. We are not aware of the millions of these worms in the soil, in ocean and freshwater habitats, in
plants, and in all kinds of other animals. Their dramatic abundance moved N.A. Cobb to write in 1914: 'If all the matter in
the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied
spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes and oceans represented by a thin
film of nematodes.' "
Major Characteristics of Phylum Nematoda
1 Body bilaterally symmetrical, cylindrical in shape;
2 Body covered with a secreted, flexible, nonliving cuticle;
3 Motile cilia and flagella completely lacking; some sensory endings derived from cilia present;
4 Muscles in body wall running in longitudinal direction only;
5 Excretory system of either one or more gland cells opening by an excretory pore, a canal system
without gland cells, or both gland cells and canals together; flame cell protonephridia lacking;
6 Pharynx usually muscular and triradiate in cross section;
7 Male reproductive tract opening into rectum to form a cloaca; female reproductive tract opening a
separate gonopore;
8 No true coelom; body cavity is the pseudocoel, a space between the gut and the mesodermal and
ectodermal components of the body wall which is not lined with peritoneum; derived from the
embryonic blastocoel rather than a secondary cavity within the mesoderm;
9 Fluid in pseudocoel enclosed by cuticle forming a hydrostatic skeleton;
Example: Ascaris
Other pseudocoelomate phyla:
Phylum Rotifera - Rotifera derive their name from their characteristic ciliated crown, or corona, which gives the
impression of a rotating wheel when beating.
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Phylum Mollusca
"Next to Arthropoda, the phylum Mollusca has the most named species in the animal kingdom -- probably about 50,000
living species, not to mention some 35,000 fossil species discovered to date. The name Mollusca indicates one of their
distinctive characteristics: a soft body."
Major Characteristics of Phylum Mollusca
1 Body bilaterally symmetrical (bilateral asymmetry in some); unsegmented, usually with definite head;
2 Ventral body wall specialized as a muscular foot, variously modified but used chiefly for locomotion;
3 Dorsal body wall forms the mantle, which encloses the mantle cavity, is modified into gills or a lung, and secretes the
shell (shell absent in some);
4 Surface epithelium usually ciliated and bearing mucous glands and sensory nerve endings;
5 Coelom mainly limited to area around heart;
6 Complex digestive system; rasping organ (radula) usually present; anus usually emptying into mantle cavity;
7 Open circulatory system (mostly closed in cephalopods) of heart (usually three-chambered), blood
vessels, and sinuses; respiratory pigments in blood;
8 Gaseous exchange by gills, lung, mantle, or body surface;
9 One or two kidneys (metanephridia) opening into the pericardial cavity and usually emptying into the mantle cavity;
10 Nervous system of paired ganglia, with nerve cords and subepidermal plexus; ganglia centralized in nerve ring in
gastropods and cephalopods;
11 Sensory organs of touch, smell, taste, equilibrium, and vision (in some); eyes highly developed in
cephalopods;
Classes of molluscs:
Class Gastropoda - "Stomach Foot" - The gastropods are by far the most numerous and diverse of the
molluscs, including about 40,000 living and 15,000 fossil species. They are usually sluggish,
sedentary animals because most of them have heavy shells and slow locomotor organs. The shell is always of one
piece and may be coiled or uncoiled.
Examples: snails, limpets, slugs, whelks, sea slugs
Class Bivalvia - "Two Valves" - These are the bivalved molluscs, most of which are sedentary filterfeeders that depend on ciliary currents produced by the gills to bring in food materials. Unlike the gastropods,
they have no head, no radula, and very little cephalization.
Examples: mussels, clams, scallops, oysters, shipworms
Class Cephalopoda - "Head Foot" - The Cephalopoda are the most complex of the molluscs. All are
marine, and all are active predators. They have a modified foot that is concentrated in the head region. It takes the
form of a funnel for expelling water from the mantle cavity. The anterior margin of the head is drawn out into a
circle or crown of tentacles.
Examples: squids, octopi, nautiluses, cuttlefish
Class Polyplacophora - Polyplacophores, or chitons, are somewhat flattened and have a convex dorsal
surface that bears eight articulating limy plates, or valves.
Example: chitons
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Phylum Annelida
The Segmented Worms
"Although a spacious, fluid-filled coelom provided an efficient hydrostatic skeleton for burrowing, precise control of body
movements was not possible in the earliest coelomates. The force of muscle contraction was carried through the body by
the fluid in the undivided coelom. This defect was remedied when a series of partitions (septa) evolved in the ancestral
annelids. When the septa divided the coelom into a series of compartments, components of most other body systems, such
as circulatory, nervous, and excretory, were repeated in each segment. This body plan is known as metamerism."
Major Characteristics of Phylum Annelida
1 Body metamerically segmented; symmetry bilateral;
2 Body wall with outer circular and inner longitudinal muscle layers; outer transparent moist cuticle
secreted by epithelium;
3 Chitinous setae, often present on fleshy appendages called parapodia; setae absent in leeches;
4 Coelom (schizocoel) well developed and divided by septa, except in leeches; coelomic fluid supplies
turgidity and functions as hydrostatic skeleton;
5 Blood system closed and segmentally arranged; respiratory pigments (hemoglobin, hemerythrin, or
chlorocruorin) often present;
6 Digestive system complete and not metamerically arranged;
7 Respiratory gas exchange through skin, gills, or parapodia;
8 Excretory system typically a pair of nephridia for each metamere;
9 Nervous system with a double ventral nerve cord and a pair of ganglia with lateral nerves in each
metamere; brain, a pair of dorsal cerebral ganglia with connectives to cord;
10 Sensory system of tactile organs, taste buds, photoreceptor cells, and eyes with lenses (in some);
11 Hermaphroditic or separate sexes; asexual reproduction by budding in some;
Classes of Annelids:
Class Polychaeta - The polychaetes are the largest class of annelids, with more than 10,000 described
species, most of them marine. They differ from other annelids in having a well-differentiated head with
specialized sense organs; paired, paddlelike appendages (parapodia) on most segments, and no clitellum.
Example: Nereis (the clamworm)
Class Oligochaeta - The more than 3,000 species of oligochaetes are found in a great variety of sizes and habitats. Most
are terrestrial or freshwater forms, but some are parasitic and a few live in brackish or marine water. With few
exceptions, they bear setae, which may be long or short,
straight or curved, blunt or needlelike, or arranged
singly or in bundles.
Examples: Lumbricus (earthworm) }
Class Hirudinea - Leeches, numbering over 500 species, are found predominantly in freshwater habitats, but a few are
marine, and some have even adapted to terrestrial life in warm, moist areas. They are usually flattened
dorsoventrally, and are found in a variety of colors - black, brown, red, or olive green. Leeches have a fixed
number of segments, usually 34, and typically have both an anterior and a posterior sucker.
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Phylum Arthropoda
"The staggering losses occasionally inflicted by the billions of locusts in Africa serve as only one reminder of our ceaseless
struggle with the dominant group of animals on earth today: the insects. With nearly 1 million species recorded, and
probably as many yet remaining to be classified, insects far outnumber all the other species of animals in the world
combined. Numbers of individuals are equally enormous. Some scientists have estimated that there are 200 million insects
for every single human alive today!"
Major Characteristics of Phylum Arthropoda
1 Bilateral symmetry; metameric body, tagmata of head and trunk; head, thorax, and abdomen; or
cephalothorax and abdomen;
2 Appendages jointed; primitively, one pair to each somite (metamere), but number often reduced;
appendages often modified or specialized;
3 Exoskeleton of cuticle containing protein, lipid, chitin, and often calcium carbonate secreted by
underlying epidermis and shed (molted) at intervals;
4 Muscular system complex, with exoskeleton for attachment; striated muscles for rapid action; smooth
muscles for visceral organs;
5 Coelom reduced; most of body cavity consisting of hemocoel (sinuses, or spaces, in the tissues) filled with blood;
6 Complete digestive system; mouthparts modified from appendages and adapted for different methods of feeding;
7 Circulatory system open, with dorsal contractile heart, arteries, and hemocoel;
8 Respiration by body surface, gills, tracheae (air tubes), or book lungs;
9 Paired excretory glands in some, homologous to metameric nephridial system of annelids; some with other excretory
organs, called malpighian tubules;
10 Nervous system of annelid plan, with dorsal brain connected by a ring around the gullet to a double nerve chain of
ventral ganglia; fusion of ganglia in some species; well-developed sensory organs;
11 Sexes usually separate, with paired reproductive organs and ducts; usually internal fertilization; often with
metamporphosis; parthenogenesis in a few forms.
Subphylum Chelicerata - The chelicerate arthropods are characterized by having six pairs of appendages that include a
pair of chelicerae, a pair of pedipalps, and four pairs of walking legs (a pair of chelicerae and five pairs of walking
legs in horseshoe crabs). They have no mandibles and no antennae. Most chelicerates suck up liquid food from
their prey.
Class Merostomata - "Thigh Mouth" - Horseshoe crabs are practically unchanged since the Triassic period,
some 225 million years ago. They have an unsegmented, horseshoe-shaped carapace, and a broad abdomen,
which has a long spinelike telson. On some of the abdominal appendages book gills are exposed. Horseshow
crabs can swim awkwardly by means of their abdominal plates and can walk on their walking legs. They feed at
night on worms and small molluscs and are harmless to humans.
Example: Limulus
Class Arachnida - Arachnids are a numerous and diverse group, with over 50,000 species described so
far. The arachnid tagmata are a cephalothorax and an abdomen, which may be distinct (as in
spiders) or nearly fused (as in ticks and mites).
Examples: Spiders (35,000 species), scorpions, ticks, mites
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Phylum Arthropoda continued
Subphylum Crustacea - The 30,000 or more species of Crustacea are mainly marine, and are the only
arthropod group that is primarily aquatic. Crustaceans are also the only arthropods with two pairs of antennae. In
addition to the antennae and mandibles, they have two pairs of maxillae on the head, followed by a pair of
appendages on each body segment. All appendages, except perhaps the first antennae, are primitively biramous
(two main branches), and at least some of the appendages of present-day adults show that condition.
Class Branchiopoda - Branchipods have reduced first antennae and second maxillae. Their legs are
flattened and leaflike and are the chief respiratory organs. The most important and successful order is the
Cladocera, which often forms a large segment of the freshwater zooplankton.
Example: Daphnia
Class Malacostraca - The class Malacostraca is the largest class of Crustacea and shows great diversity.
The trunk usually has eight thoracic and six abdominal somites, each with a pair of appendages.
There are many freshwater and marine species.
Examples: Lobsters, crabs, crayfish, shrimp
Subphylum Uniramia - The appendages of uniramian arthropods are unbranched. This subphylum includes the insects
and the myriapods (centipedes and millipedes). The myriapods have evolved a pattern of two tagmata (head and
trunk) with paired appendages on most or all trunk somites. Uniramian arthropod heads resemble the crustacean
head but have only one pair of antennae, instead of two. They also have mandibles and two pairs of maxillae (one
pair in millipedes). Respiratory exchange is by body surface and tracheal systems, although juveniles, if aquatic,
may have gills.
Class Chilopoda - "Lip Feet" - Centipedes are active predators with a preference for moist places such as
under logs or stones, where they feed on earthworms, insects, etc. Their bodies are somewhat
flattened dorsoventrally and they may contain from a few to 177 somites. Each somite, except the one behind the
head and the last two, bears one pair of appendages.
Class Diplopoda - "Two Feet" - Millipedes have cylindrical bodies made up of 25 to 100 segments. The
four thoracic segments bear only one pair of legs each, but the abdominal segments each have two pairs.
Millipedes are less active than centipedes and are generally herbivorous, living on decayed plant and animal matter
and sometimes living plants.
Class Insecta - The insects are the most numerous and diverse of all the groups of arthropods. There are
more species of insects than species in all the other classes of animals combined!! Insects differ from other
arthropods in having three pairs of legs and usually two pairs of wings on the thoracic region of the body, although
some have one pair of wings, or none. In size, insects range from less than 1 mm to 20 cm in length, the majority
being less than 2.5 cm long. The insect tagmata are the head, thorax, and abdomen. The head usually bears a pair
of relatively large compound eyes, a pair of antennae, and usually three ocelli.
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Phylum Echinodermata
"Despite the adaptive value of bilaterality for free-moving animals, and the merits of radial symmetry for sessile animals,
echinoderms confounded the rules by becoming free-moving but radial. That they evolved from a bilateral ancestor there
can be no doubt, for their larvae are bilateral. They undergo a bizarre metamorphosis to a radial adult in which there is a
90o reorientation in body axis, with a new mouth arising on the left side and a new anus appearing on the right side. [...]
This constellation of characteristics is unique in the animal kingdom. It has both defined and limited the evolutionary
potential of the echinoderms."
Major Characteristics of Phylum Echinodermata
1 Body not metameric, adult with radial, pentaramous symmetry (pentaradial) characterized by five or more radiating
areas;
2 No head or brain; few specialized sensory organs;
3 Nervous system with circumoral ring and radial nerves;
4 Endoskeleton of dermal calcareous ossicles with stereom (meshwork) structure; covered by an epidermis
(ciliated in most); pedicellariae (in some);
5 A water-vascular system of coelomic origin that extends from the body surface as a series of tentacle-like projections
(podia or tube feet);
6 Locomotion by tube feet, which project from the ambulacral areas, or by movement of spines, or by
movement of arms, which project from central disc of body;
7 Digestive system usually complete; axial or coiled; anus absent in ophiuroids;
8 Coelom extensive, forming the perivisceral cavity and the cavity of the water-vascular system; enterocoel;
9 So-called hemal system present, of uncertain function but playing little, if any, role in circulation, and
surrounded by extensions of coelom;
10 Respiration by dermal branchiae, tube feet, respiratory tree (holothuroids), and bursae (ophiuroids);
11 Excretory organs absent;
12 Sexes separate (except a few hermaphroditic); fertilization usually external;
13 Development through free-swimming, bilateral, larval stages (some with direct development);
metamorphosis to radial adult or subadult form;
Classes of Echinoderms:
Class Asteroidea - Sea stars typically have five arms (though they may have more) which merge
gradually with the central disc. On the aboral surface can be found the madreporite and many spines, with
pedicellariae at the base of the spines. The oral, or under, side, features the mouth in the center, and ambulacral
grooves radiating out along each arm. The tube feet project from these grooves.
Example: Sea star
Class Ophiuroidea - Brittle stars differ from the sea stars in many ways. They also typically have five arms, but these
arms are slender and distinctly set off from the central disc. They have no pedicellariae, and their ambulacral
grooves are closed. The tube feet have no suckers, and are of limited use in locomotion; the brittle stars use their
entire arms to aid in movement. The madreporite of the ophiuroids is located on the oral surface, and they do not
have an anus: indigestible material is expelled from the mouth.
Example: Brittle stars
Class Echinoidea - Echinoids have a compact body encased in test, or shell. The dermal ossicles, which are modified to be
close-fitting plates, make up the test. Echinoids lack arms, but their pentaradial structure is evident in the
arrangement of the ambulacral areas, appearing as grooves on the test that run from the mouth to the aboral side,
ending at the area around the anus. "Regular" sea urchins are the familiar hemispherical shape with medium to
long spines. They move by means of their tube feet, with some assistance from their spines. "Irregular" urchins,
the sand dollars, have become secondarily bilateral: their spines are usually very short and their bodies are more
flattened than those of regular urchins. They move chiefly by their spines.
Examples: Sea urchins, sand dollars
Class Holothuroidea - Sea cucumbers are greatly elongated along the oral-aboral axis compared to the other echinoderms,
and the ossicles are much reduced in most, so the animals are soft-bodied. They too have become secondarily
bilateral, though in a different way from the irregular urchins: their tube feet are well developed along only one
ambulacral groove.
Example: Sea cucumbers
Class Crinoidea - In crinoids, the body disc has a leathery skin containing calcareous plates. Five flexible arms branch to
form many more arms, each with many lateral pinnules arranged like barbs on a feather. Their ambulacral
grooves are open and ciliated, and serve to catch small organisms and carry them to the mouth.
Examples: Sea lilies and feather stars
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Phylum Chordata
"The four distinctive characteristics that, taken together, set chordates apart form all other phyla are the notochord; single,
dorsal, tubular nerve cord; pharyngeal pouches; and post anal propulsive tail. These characteristics are always
found at some embryonic stage, although they may be altered or may disappear altogether in later stages of the life cycle."
Major Characteristics of Phylum Chordata
1 Bilateral symmetry; segmented body; three germ layers; well-developed coelom.
2 Notochord (a skeletal rod) present at some stage in life cycle.
3 Single, dorsal, tubular nerve cord; anterior end of cord usually enlarged to form brain.
4 Pharyngeal gill slits present at some stage in life cycle.
5 Post anal tail, usually projecting beyond the anus at some stage but may or may not persist.
6 Segmented muscles in an unsegmented trunk.
7 Ventral heart, with dorsal and ventral blood vessels; closed blood system.
8 Complete digestive system.
9 A cartilaginous or bony endoskeleton present in the majority of members (vertebrates).
Subphylum Urochordata - "Tail Cord." There are approximately 1500 described species of these marine living chordates.
They are commonly called tunicates because of the tough, nonliving tunic that surrounds the animal. The
swimming larvae resemble tadpoles and possess all of the four key chordate characteristics. As sessile adults they
lose the notochord and the tail, their dorsal hollow nerve cord becomes reduced, but they retain the pharyngeal gill
slits.
Example: tunicates, sea squirts
Subphylum Cephalochordata - "Head Cord." There are only 25 species described in this subphylum of marine lancelets.
They are all small, slender, laterally compressed, translucent animals. These simple animals are often used as a
textbook example to represent the four key chordate characteristics. Once considered to be the ancestor of the
chordates, they are still believed to more closely resemble the earliest prevertebrates than any other animal known.
Examples: Amphioxus (the lancelets)
Subphylum Vertebrata - "Backboned." This is the largest and most diverse subphylum of chordates whose
evolution has been guided by the basic adaptations of the living endoskeleton, efficient respiration, advanced
nervous system, and paired limbs. This group is divided into those without jaws and those with jawed mouths.
This course will take a close look at this subphylum so we have included separate pages for most of the taxonomic
classes for this group.
Examples: lampreys, sharks, fish, frogs, snakes, pigeons, pigs, humans
Superclass Agnatha ("Without jaws"): Those vertebrates without true jaws or appendages including the
hagfishes and the lampreys.
Superclass Gnathostomata ("Jawed mouth"): Those vertebrates with jaws and usually with paired
appendages.
Class Chondrichthyes - The cartilaginous fishes. Examples: sharks, skates, rays.
Class Osteichthyes - The bony fishes. Examples: perch, goldfish, trout.
Class Amphibia - The amphibians. Examples: frogs, toads, salamanders.
Class Reptilia - The reptiles. Examples: snakes, lizards, turtles.
Class Aves - The birds. Examples: pigeons, ostriches, hawks, robins.
Class Mammalia - The mammals. Examples: mice, monkeys, whales, lions
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Phylum Chordata,
Subphylum Vertebrata,
Superclass Gnathostomata,
Class Amphibia
"The early members of the class Amphibia, of which chorusing frogs are among the more vociferous modern descendants,
originated not in weeks but over millions of years by a lengthy series of alterations that cumulatively fitted the vertebrate
body plan for life on land. The origin of land vertebrates is no less a remarkable feat for this fact-a feat that incidentally
would have a poor chance of succeeding today because well-established competitors make it impossible for a poorly
adapted transitional form to gain a foothold."
Major Characteristics of Class Amphibia:
1 Skeleton mostly bony.
2 Body forms vary greatly from an elongated trunk with distinct head, neck and tail to a compact,
depressed body with fused head and trunk and no intervening neck.
3 Usually four limbs; webbed feet often present; forelimb usually with four digits.
4 Skin smooth and moist with many glands, some of which may be poison glands; no scales.
5 Mouth usually large with small teeth.
6 Respiration by lungs, skin and gills, either separately or in combination; external gills in the larval form and may persist
throughout life in some.
7 Three-chambered heart.
8 Ectothermal.
9 Separate sexes; fertilization mostly internal in salamanders and caecilians and mostly external in frogs and toads.
Orders of Class Amphibia:
Order Gymnophiona - The caecilians.
Order Caudata - The salamanders and newts.
Order Anura - The frogs and toads.
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Phylum Chordata,
Subphylum Vertebrata,
Superclass Gnathostomata,
Class Reptilia
The reptiles have several characteristics that distinguish them from the amphibians: "Reptiles have tough, dry, scaly skin,
offering protection against desiccation and physical injury.[...] The shelled (amniotic) egg of reptiles contains food and
protective membranes for supporting embryonic development on dry land.[...] Reptilian jaws are efficiently designed for
applying crushing or gripping force to prey.[...] Reptiles have some form of copulatory organ permitting internal
fertilization.[...] Reptiles have a more efficient circulatory system and higher blood pressures than amphibians.[...] Reptile
lungs are better developed than those of amphibians.[...] Reptiles have evolved efficient strategies for water
conservation.[...] All reptiles, except the limbless members, have better body support than the amphibians and more
efficiently designed limbs for travel on land.[...] The reptilian nervous system is considerably more advanced than that of
the amphibian."
Major Characteristics of Class Reptilia:
1 Body covered with horny epidermal scales.
2 Paired limbs, usually with five toes, adapted for climbing, running or paddling, absent in snakes and some lizards.
3 Skeleton well ossified.
4 Respiration by lungs, no gills.
5 Three-chambered heart in most (crocodiles have four-chambered heart).
6 Ecothermic, behaviorally thermoregulate.
7 Internal fertilization and separate sexes.
8 Eggs covered with shells that contain extraembryonic membranes (amnion, chorion, yolk sac, and
allantois).
Orders of Class Reptilia:
Order Squamata - The lizards and snakes.
Order Testudines - The turtles.
Order Crocodilia - The crocodiles and alligators.
Order Sphenodonta - The tuatara from New Zealand.
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Phylum Chordata,
Subphylum Vertebrata,
Superclass Gnathostomata,
Class Aves
"Zoologists had long recognized the similarity of birds and reptiles because of their many shared morphological,
developmental, and physiological homologies."
"Just as an airplane must be designed and built according to rigid aerodynamic specifications if it is to fly, so too must birds
meet stringent structural requirements if they are to stay airborne. All the special adaptations found in flying birds
contribute to two things: more power and less weight."
Major Characteristics of Class Aves:
1 Body usually spindle-shaped, with four divisions: head, neck, trunk, and tail; neck disproportionately long for balancing
and food gathering.
2 Paired limbs, with the forelimbs usually adapted for flying; posterior pair variously adapted for
perching, walking, and swimming; foot with four toes.
3 Epidermal covering of feathers and leg scales.
4 Skeleton fully ossified, with air cavities; beak with no teeth; single bone in middle ear.
5 Nervous system well developed.
6 Four-chambered heart.
7 Endothermic
8 Respiration by slightly expansible lungs with thin air sacs; syrinx near junction of trachea and bronchi.
9 Sexes separate.
10 Fertilization internal; amniotic eggs with much yolk and hard calcareous shells.
Some Orders of Class Aves:
Order Gaviiformes - The loons.
Order Pelecaniformes - The pelicans, cormorants and others.
Order Anseriformes - The geese, swans and ducks.
Order Falconiformes - The hawks, eagles, vultures, falcons, condors and buzzards.
Order Galliformes - The grouse, pheasants, turkeys, ptarmigans and domestic fowl.
Order Columbiformes - The pigeons and doves. {coming soon: Pigeon Dissection Home Page}
Order Psittaciformes - The parrots and parakeets.
Order Strigiformes - The owls.
Order Passeriformes - The perching song birds.
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Phylum Chordata,
Subphylum Vertebrata,
Superclass Gnathostomata,
Class Mammalia
"Mammals, with their highly developed nervous system and numerous ingenious adaptations, occupy almost every
environment on earth that supports life. Although not a large group (approximately 4450 species as compared with more
than 9000 species of birds, approximately 21,700 species of fishes, and nearly one million species of insects), the class
Mammalia is overall the most biologically differentiated group in the animal kingdom."
Major Characteristics of Class Mammalia:
1 Body covered with hair, reduced in some.
2 Integument with sweat, scent, sebaceous and mammary glands.
3 Mouth with teeth.
4 Movable eyelids and fleshy external ears.
5 Four limbs in most, adapted for many forms of locomotion.
6 Four-chambered heart.
7 Respiration system with lungs and larynx; muscular diaphragm.
8 Brain highly developed.
9 Endothermic and homeothermic.
10 Internal fertilization; eggs developed in a uterus with placental attachment (except in monotremes); fetal membranes
(amnion, chorion, allantois).
11 Young nourished by milk from mammary glands.
Infraclass Ornithodelphia - Order Monotremata: The egg-laying mammals, duck-billed platypus & spiny anteater.
Infraclass Metatheria - Order Marsupialia: The pouched mammals, opossums, kangaroos & koala.
Infraclass Eutheria - The placental mammals:
Order Insectiovora: The shrews, hedgehogs and moles.
Order Chiroptera: The bats.
Order Primates: The prosimians, monkeys, apes and humans.
Order Xenarthra: The sloths, anteaters and armadillos.
Order Lagomorpha: The rabbits, hares and pikas.
Order Rodentia: The squirrels, rats, mice and woodchucks.
Order Cetacea: The whales, dolphins and porpoises.
Order Carnivora: The dogs, wolves, cats, bears and weasels.
Order Pinnipedia: The sea lions, seals, sea elephants and walruses.
Order Proboscidea: The elephants.
Order Perissodactyla: The horses, asses, zebras, tapirs and rhinoceroses.
Order Artiodactyla: The swine, deer, camels, hippopotamuses, giraffes, antelopes, cattle, pronghorn, sheep and
goats.