1. Systematics- studies diversity of life
It is the study and classification of
organisms with the goal of
reconstructing their evolutionary history
Taxonomy- the field of science that
classifies life into groups.
3. Classification: Six kingdom system
:
Eubacteria Archaebacteria
Monera
E. coli Cyanobacteria
Protista
Paramecium Diatom Slime mold
Plantae
Fungi
Animalia
4. Carolus Linnaeus (Father of
classification)
Swedish doctor
Professor of Medicine & Natural
History
Wrote 14 books in 3 years
Fish book: 3,000 pages
5. Carolus Linnaeus
1753: published book
describing World’s
plants(Species plantarum)
Started naming process
(Binomial Nomenclature)
6. Binomial Nomenclature
System of assigning names to
Organisms where an organism was
given two names (genus + species)
Loxodonta africanas
Loxodonta africanas
12. Advantages of using Scienfific
names:
1. Agreed upon system – One
organism is assigned one
scientific name the world.
2. Names are given using highly
technical process.
21. Kingdom Protista
General characteristics:
1. They are Eukaryotic
2. Generally single-celled; if multicellular,
cells not organized into tissues
3. Heterotrophic & autotrophic forms
4. There are three (3) informal groups:-
Plant-like (algal) protists
Animal-like protists
Fungus-like protists
32. Kingdom Fungi
General characteristics
1. Eukaryotic
2. Generally multicellular, organisms (a
few species, e.g., yeast are unicellular).
3. Nutrition:
Heterotrophic
Saprophytic (absorptive)
33. Kingdom Fungi
4. Most with cell walls (usually
composed of chitin) and complex
life histories.
5. Includes molds, yeasts, rusts, and
mushrooms, marine fungi
37. Kingdom Animalia
5. Most exhibit significant capacity for
locomotion.
6. Cells not surrounded by cell walls.
7. Includes sponges, sea anemones,
snails, insects, sea stars, fish,
reptiles, birds, and human beings.
38. Phylum of Kingdom ANIMALIA
1.Phylum Aschelimnthes
(Roundworms = Nematoda)
2.Phylum Platyhelimnthes
(Flatworms)
3.Phylum Annelida
4.Phylum Arthropoda
5.Phylum Chordata.
40. Phylum Nematoda
General characteristics:
1. Roundworms ~ cylinrical body with
tapering ends.
2. They have Primitive body cavity
(Acoelomate)
3. They have Gut only one opening
which is Mouth& Anus.
4. They have No circulatory system
41. 4. Nervous system
5. Very successful- well adapted to
every ecosystem
6. Many are parasites
43. Phylum Platyhelminthes
Platy~Flat and Heliminthes ~worm
General characteristics:
1. Consists of Flatworms ribbon like
worms.
2. Blind digestive cavity
3. Bilaterally symmetrical
4. Thin, simple circulation
5. Sensory organs at front
6. Many parasitic
45. Phylum Annelida
Class Class Class
Oligochaeta Polychaeta Hirudinea
earthworms marine worms leaches
46. Economic importance of Annelids:
1.Earthwom (Lumbricus terresteris ) plays
important role in soil formation,it is found in dampy
or humid soil rich in decaying leaves and organic
matters.
2.Leach of class Hirudinea is an acquatic blood
feeder may play part in transmission of blood
borne diseases eg Hepatitis C.
3.Marine worms form part of marine animals such
as fish e,t,c
47. Phylum Arthropoda
General characteristics:
1. Insects, crabs, spiders, barnacles
2. Most species; 80% are insects
3. They have Hard chitinous exoskeleton
( which must shed to allow grow)
48. Characteristics…..cont…
4. Have Open Circulatory system with
blood, heart
5. Have special gas exchange system
6. Have developed sensory organ
including antennae and true eyes.
7. They have body segments and
appendeges.
49. CLASSES OF THE PHYLUM
ARTHROPODA
1.Class Arachnida
2.Class Crustacea
3.Class Insecta
4.Class Diplopoda
5.Class Chilopoda
50. Class Arachnida
(Spiders, Scorpions, Ticks & Mites)
Characteristics.
1.Very diverse class
2.Most species parasitic or predatory.
3.Many possess book lungs for gas
exchange.
4.Spiders are able to produce a strong
polymer – silk.
51. Class Arachnida.
(arachnids, horseshoe crabs & sea spiders)
5. Body divided into 2 regions
– Abdomen
– Cephalothorax (fused head & thorax)
6. Lack jaws (Do not have jaws)
7. Have 6 appendages & no antennae
– First appendages form chilicerae
(frequently fangs)
52. Class Arachnids
• Spiders
• Scorpions ??
Economic importance:
1. They sting producing
very painful stimulus
2. They can play part in
biological control
3. They produce silk
polymer which is
important raw material
in textile industries.
55. Class Crustacea
Characteristics:
1.Includes crabs, lobsters, crayfish,
shrimp, & barnacles
2.Appendages are often highly specialized
3.Gas exchange is usually through gills
4.Many species taste delicious in butter
( They are source of food across culture)
61. Class Diplopoda
Centipede:
1. Segmented body
2. Each segment with one pair
of legs
3. The first legs modified to
fangs (poisonous claws)
4.They are Carnivorous
62. Class Diplopoda
Millipedes:
1. Cylindrical segmented body.
2. Each segment carries two pair of walking legs
3. They are herbivorous & Decomposers.
4. They do not have poisonous claws
63. Class Insecta
– Class Insects:
1. Body divided into three
parts (tagma)
• Head, thorax, abdomen
• Majority of all arthropods
are found in this class.
65. Tagmosis
Thorax is divided into three portion each of
which carries one pair of walking legs.
• Thorax (~ 3-6
These portions are:- prothorax,mesothoax
segments) and metathorax.
– locomotion,
grasping.
• Thoracic
appendages
– walking legs,
– wings
– chelipeds
65
66. Class Insecta (the insects)
2. Far & away the most diverse of animal
groups
– More types of insects alone than all other
animal groups combined
3. Inhabit all terrestrial & freshwater
ecosystems.
Success largely attributed to coevolution
with flowering plants.
67. Insect Body Plan
4. Insects have 6 legs ( three pairs)
• 5. Body divided in to three parts
namely:-
– Head
– Thorax
– Abdomen
6. Most insects have wings, however in
many species these are vestigal (wings
are found on the second or second and 3rd
abdominal segment.
68. Characteristics cont…
7. Have advanced
excretory system
composed of
malphygian tubules
8. Exchange gasses
through a complex
tracheal system
(there are spiracles
on some of the body
segment)
69. Vision
9. Have complex compound eye which is usually
extremely sensitive to motion and allows 3600 vision
• Most insects see well into the UV spectrum
70. Feeding / Mouthparts
10. Insects usually have
specialized
jaws/mouthparts suited
to their ecological niche
11. They have only one
pair of antennae.
71. Metamorphosis
• Most insects undergo a process of metamorphosis - 2 types
• Incomplete metamorphosis
– Larva similar to adult, with differing body proportions
– Undergoes a series of molts resulting in adult phenotype
72. Complete Metamorphosis
• Larva is very unlike adult phenotype
• Envelopes self in a coccoon or chrysalis where body
breaks-down and reforms into adult form.
73. Economic importances of insects:
1. Some insects such as Grasshopper they sources of
food.
2. Insect larvae e.g. Army worms and Adult
grasshoppers can destruct crops,
3. Vectors of diseases e.g. cockroach and housefly
may be mechanical vector of gastro enteric fever
4. Termites destroy properties e.g. timbers at the same
times they are edible.
5. Moth and butterflies are ornamental
6. Spider produces silk polymer which is very useful
in textiles industries,
78. Class Osteichthyes
Characteristics
1. Posses jaws with teeth and bony skeleton.
2. They have paired fins that are equipped with
muscles and endoskeleton.
3. They breathe by mean of gills and have 4 paired
gill arches covered by operculum
3. Intestine- simple, no spiral valve
4.They posses Swim bladder (air sacs)
5. Lateral line
82. Class Amphibia
Characteristics
• Cold blooded
• Returns to water to breed
• Metamorphosis
• Some toxic
• Estivation-dry and hot
• Hibernation- cold
90. STUDY QUESTIONS
1. What is the difference between a prokaryote
and eukaryote?
2. Which kingdoms are prokaryote and which
are eukaryote?
3. Define a species.
4. How do fungus feed?
5. What are some key characteristics of
mammals?
Editor's Notes
Nematodes have successfully adapted to nearly every ecosystem from marine to fresh water, from the polar regions to the tropics, as well as the highest to the lowest of elevations. They are ubiquitous in freshwater, marine, and terrestrial environments, where they often outnumber other animals in both individual and species counts, and are found in locations as diverse as Guam and oceanic trenches . They represent, for example, 90% of all life on the seafloor of the Earth. [ 3 ] Their many parasitic forms include pathogens in most plants and animals (including humans ). Some nematodes can undergo cryptobiosis . Nematodes are the most speciose phylum after the arthropods, they occur in nearly every habitat including as parasites in all sorts of plants and animals, (they don't like dry places however). One species is known that can live in old vinegar (Turbatrix aceti)and another that as only been found in German beer mats. Though only about 80 000 species have been described some scientists estimate there may be as many as a million species all told. They can occur in very dense numbers in the soil and rotting vegetation, as many as 90 000 have been found in a single rotting apple, while millions occur in the top 3cm (1 inch) of a square metre of good quality soil. While there are a huge number of free living Nematodes there are also a large number of parasitic species, many of which cause diseases to man and other animals as well as to plants, nearly every living organism has been found to be parasitised by one species of nematode or another. Most nematodes are reasonably small, they range in size from 100 micrometres in length (1/10th of a mm or 1/250th of an in) to the female Giant Nematode Dioctophyme renale which may be up to 1 metre, or 3 ft long. Ecology Nematodes live in a vast variety of habitats, ecologically they can be divided into free living forms and parasitic forms. Free living forms have a simple life cycle involving 4 juvenile instars on the path from egg to adult. Parasitic species have developed a wide range of variations on this basic theme. The variations involve whether there is a secondary host and the amount of time spent in one or either hosts. There is also considerable variability in the way that they move from one host species to another. thus while many species lay eggs that pass out of the primary host with the faeces where they are eaten by the secondary host which then gets eaten in turn by the primary host after the Nematodes have developed. Because it is not always totally reliable that the secondary host will be eaten just as the Nematode larvae have developed into the infective stage many species have the ability to encyst themselves in the muscle or cuticle of their secondary hosts. Some species use another animal to transport them from one host to another thus Wuchereria bancrofti releases minute live young called 'microfilaria' into the primary hosts blood stream rather than eggs into the digestive tract. These microfilaria get ingested by mosquitoes when they feed on an infected person. Inside the mosquito they live in the mosquitoes gut where they develop until the Larva 3 stage wait for the mosquito to bite another host whereupon they enter the host via the mosquitoes proboscis sheath and the wound it makes in the hosts skin. Nematodes in Mankind Human beings, along with all other living things are host to numerous Nematode parasites. The most common of these is Ascaris lumbricoides with an estimated 700 million people effected globally, this Nematode is not normally fatal and in low numbers may have very little effect on adults, however in heavy doses it can be quite debilitating, especially for children . The Nematodes infecting mankind include several species of filarial worms, the most important of these are Wuchereria bancrofti and Brugia malayi which are very similar and cause lymphatic filariasis, Onchocerca volvulus which causes River Blindness and Loa loa which causes Loiasis. Other species are Dranunculus medinensis known as Guinea Worm, Trichinella spiralis causing Trichinosis, Necator americanus and Ancylostoma duodenale causing Hookworm, Enterobius vermicularis causing Pinworms and Trichuris trichuria causing Whipworm or Trichuriasis. Anatomy Basically a Nematode is a long hollow tube within which is another tube, the alimentary canal and the reproductive organs. Nematodes are round in cross section, this is because unlike the other worms that below them in the phyla table they maintain their body fluids under great pressure (on average internal pressure in a nematode equals 70mm of mercury or 1.49 PSI, with a maximum recorded value of 125mm of mercury or 2.41 PSI). To contain this high pressure nematodes have an extremely tough, yet elastic and flexible cuticle. This cuticle consists of up to 9 layers of proteinaceous fibres, with 3 layers being easily discerned, these are called, from the outside in, the cortex, the matrix layer and the fibre layer. Despite its complexity the Nematode cuticle is permeable to both water and gases, so respiration occurs through it. Beneath the cuticle is a hypodermis and a layer of longitudinal muscle. The combination of the flexure of these muscles with the high pressure of the system produces a characteristic whip-like wriggle that Nematodes use to swim. Scientifically this is called undulatory propulsion with sinusoidal waves passing back along the body. At the anterior (head) end there is a mouth which has 3 lips behind which predatory species possess a few teeth, this leads to a pharynx which is triangular in cross section. Because of the high pressure within the body unsupported organs such as the intestines tend to collapse in much the same way that an uninflated bicycle tube tends to become oval or flat in cross section when laid flat on the table. The pharynx of Nematodes is an efficient pump and forces food into the intestines, there is a one way valve between the intestines and the pharynx. The pharynx can, when this valve is closed, be used to suck liquid food into the mouth. Digestion is rapid and faeces are expelled under pressure. This pressure is so great that the parasitic nematode Ascaris lumbricoides which is about 12cm to 18cm long (5 to 7 inches) may shoot its faeces 60cm or 2 feet into the air. Nematodes, especially free living forms generally have a reasonably well developed nervous system. This is comprised of a circum-pharyngeal nerve ring made up from 4 nerve ganglia from which 6 longitudinal nerves extend down through the body to the various parts of the gut and the reproductive organs. There are also 6 shorter nerves which extend forwards from the circum-pharyngeal ganglia towards the mouth. Nematodes have no circulatory or respiratory organs and the excretion of metabolic waste is via two simple ducts or tubules which have no nephridia or flame cells. Nematodes are copiously reproductive and most of their body cavity, which is a pseudocoelom is filled with paired sets of reproductive organs, either ovaries or testes. Males and females copulate and the male introduces sperm to the females vagina with the help of 2 stiff horny spicules that are a part of his cloaca. Fertilisation is internal and females lay eggs over a prolonged time period, thus a female Ascaris lumbricoides may lay her eggs at the rate of 200,000 per day and have had a total 27 million eggs within her at the start of her reproductive career. Young nematodes hatch from these eggs and go through 4 moults before they become adults. Anatomy Nematodes are slender, worm-like animals, typically less than 2.5 millimetres (0.10 in) long. The smallest nematodes are microscopic, while free-living species can reach as much as 5 centimetres (2.0 in) and some parasitic species are larger still. The body is often ornamented with ridges, rings, warts, bristles or other distinctive structures. [ 11 ] The head of a nematode is relatively distinctive. Whereas the rest of the body is bilaterally symmetrical, the head is radially symmetrical, with sensory bristles and, in many cases, solid head-shields radiating outwards around the mouth. The mouth has either three or six lips, which often bear a series of teeth on their inner edge. An adhesive caudal gland is often found at the tip of the tail. [ 11 ] The epidermis is either a syncytium or a single layer of cells, and is covered by a thick collagenous cuticle. The cuticle is often of complex structure, and may have two or three distinct layers. Underneath the epidermis lies a layer of muscle cells. Projections run from the inner surface of these cells towards the nerve cords; this is a unique arrangement in the animal kingdom, in which nerve cells normally extend fibres into the muscles rather than vice versa . [ 11 ] The muscle layer surrounds the body cavity, which is filled with a fluid that lacks any form of blood cells. The gut runs down the centre of the cavity. [ 11 ] Digestive system The oral cavity is lined with cuticle, which is often strengthened with ridges or other structures, and, especially in carnivorous species, may bear a number of teeth. The mouth often includes a sharp stylet which the animal can thrust into its prey. In some species, the stylet is hollow, and can be used to suck liquids from plants or animals. [ 11 ] The oral cavity opens into a muscular sucking pharynx , also lined with cuticle. Digestive glands are found in this region of the gut, producing enzymes that start to break down the food. In stylet-bearing species, these may even be injected into the prey. [ 11 ] There is no stomach, with the pharynx connecting directly to the intestine that forms the main length of the gut. This produces further enzymes, and also absorbs nutrients through its lining. The last portion of the intestine is lined by cuticle, forming a rectum which expels waste through the anus just below and in front of the tip of the tail. The intestine also has valves or sphincters at either end to help control the movement of food through the body. [ 11 ] Excretory system Nitrogenous waste is excreted in the form of ammonia through the body wall, and is not associated with any specific organs. However, the structures for excreting salt to maintain osmoregulation are typically more complex. [ 11 ] In many marine nematodes, there are one or two unicellular renette glands that excrete salt through a pore on the underside of the animal, close to the pharynx. In most other nematodes, these specialised cells have been replaced by an organ consisting of two parallel ducts connected by a single transverse duct. This transverse duct opens into a common canal that runs to the excretory pore. [ 11 ] Nervous system Four nerves run the length of the body on the dorsal, ventral, and lateral surfaces. Each nerve lies within a cord of connective tissue lying beneath the cuticle and between the muscle cells. The ventral nerve is the largest, and has a double structure forward of the excretory pore. The dorsal nerve is responsible for motor control, while the lateral nerves are sensory, and the ventral combines both functions. [ 11 ] At the anterior end of the animal, the nerves branch from a dense circular nerve ring surrounding the pharynx, and serving as the brain. Smaller nerves run forward from the ring to supply the sensory organs of the head. [ 11 ] The body of nematodes is covered in numerous sensory bristles and papillae that together provide a sense of touch. Behind the sensory bristles on the head lie two small pits, or amphids . These are well supplied with nerve cells, and are probably chemoreception organs. A few aquatic nematodes possess what appear to be pigmented eye-spots, but is unclear whether or not these are actually sensory in nature. [ 11 ] Reproduction Most nematode species are dioecious , with separate male and female individuals. Both sexes possess one or two tubular gonads . In males, the sperm are produced at the end of the gonad, and migrate along its length as they mature. The testes each open into a relatively wide sperm duct and then into a glandular and muscular ejaculatory duct associated with the cloaca . In females, the ovaries each open into an oviduct and then a glandular uterus . The uteri both open into a common vagina, usually located in the middle of the ventral surface. [ 11 ] Reproduction is usually sexual. Males are usually smaller than females (often much smaller) and often have a characteristically bent tail for holding the female for copulation . During copulation, one or more chitinized spicules move out of the cloaca and are inserted into genital pore of the female. Amoeboid sperm crawl along the spicule into the female worm. Nematode sperm is thought to be the only eukaryotic cell without the globular protein G-actin . Eggs may be embryonated or unembryonated when passed by the female, meaning that their fertilized eggs may not yet be developed. A few species are known to be ovoviviparous . The eggs are protected by an outer shell, secreted by the uterus. In free-living roundworms, the eggs hatch into larvae, which appear essentially identical to the adults, except for an under-developed reproductive system; in parasitic roundworms, the life cycle is often much more complicated. [ 11 ] Nematodes as a whole possess a wide range of modes of reproduction. [ 12 ] Some nematodes, such as Heterorhabditis spp., undergo a process called : intrauterine birth causing maternal death. [ 13 ] Some nematodes are hermaphroditic , and keep their self-fertilized eggs inside the uterus until they hatch. The juvenile nematodes will then ingest the parent nematode. This process is significantly promoted in environments with a low or reducing food supply. [ 13 ] The nematode model species Caenorhabditis elegans and C. briggsae exhibit androdioecy , which is very rare among animals. The single genus Meloidogyne (root-knot nematodes) exhibit a range of reproductive modes including sexual reproduction , (in which most, but not all, generations reproduce asexually), and both meiotic and mitotic parthenogenesis . The genus exhibits an unusual form of parthenogenesis, in which sperm-producing males copulate with females, but the sperm do not fuse with the ovum. Contact with the sperm is essential for the ovum to begin dividing, but because there is no fusion of the cells, the male contributes no genetic material to the offspring, which are essentially clones of the female. [ 11 ] Free-living species In free-living species, development usually consists of four molts of the cuticle during growth. Different species feed on materials as varied as algae, fungi, small animals, fecal matter, dead organisms and living tissues. Free-living marine nematodes are important and abundant members of the meiobenthos . They play an important role in the decomposition process, aid in recycling of nutrients in marine environments and are sensitive to changes in the environment caused by pollution. One roundworm of note is Caenorhabditis elegans , which lives in the soil and has found much use as a model organism . C. elegans has had its entire genome sequenced, as well as the developmental fate of every cell determined, and every neuron mapped. [Parasitic species Nematodes commonly parasitic on humans include ascarids ( Ascaris ), filarias , hookworms , pinworms ( Enterobius ) and whipworms ( Trichuris trichiura ). The species Trichinella spiralis , commonly known as the trichina worm , occurs in rats, pigs, and humans, and is responsible for the disease trichinosis . Baylisascaris usually infests wild animals but can be deadly to humans as well. are Heartworms known for causing Heartworm disease by inhabiting the hearts, arteries, and lungs of dogs and some cats. Haemonchus contortus is one of the most abundant infectious agents in sheep around the world, causing great economic damage to sheep farms. In contrast, entomopathogenic nematodes parasitize insects and are considered by humans to be beneficial. One form of nematode is entirely dependent upon fig wasps , which are the sole source of fig fertilization. They prey upon the wasps, riding them from the ripe fig of the wasp's birth to the fig flower of its death, where they kill the wasp, and their offspring await the birth of the next generation of wasps as the fig ripens. A newly discovered parasitic tetradonematid nematode, Myrmeconema neotropicum , apparently induces fruit mimicry in the tropical ant Cephalotes atratus . Infected ants develop bright red gasters, tend to be more sluggish, and walk with their gasters in a conspicuous elevated position. These changes likely cause frugivorous birds to confuse the infected ants for berries and eat them. Parasite eggs passed in the bird's feces are subsequently collected by foraging Cephalotes atratus and are fed to their larvae , thus completing the life cycle of Myrmeconema neotropicum . [ 14 ] Colorized electron micrograph of soybean cyst nematode ( Heterodera sp.) and egg Plant parasitic nematodes include several groups causing severe crop losses. The most common genera are Aphelenchoides (), Ditylenchus , Globodera (potato cyst nematodes), Heterodera (soybean cyst nematodes), , Meloidogyne (root-knot nematodes), , Pratylenchus (lesion nematodes), and Xiphinema (dagger nematodes). Several phytoparasitic nematode species cause histological damages to roots, including the formation of visible galls (e.g. by root-knot nematodes), which are useful characters for their diagnostic in the field. Some nematode species transmit plant viruses through their feeding activity on roots. One of them is Xiphinema index , vector of GFLV ( Grapevine Fanleaf Virus ), an important disease of grapes. Other nematodes attack bark and forest trees. The most important representative of this group is Bursaphelenchus xylophilus , the pine wood nematode, present in Asia and America and recently discovered in Europe. [ edit ] Agriculture and horticulture Depending on the species, a nematode may be beneficial or detrimental to plant health. From agricultural and horticulture perspectives, there are two categories of nematode: predatory ones, which will kill garden pests like cutworms, and pest nematodes, like the root-knot nematode, which attack plants and those that act as vectors spreading plant viruses between crop plants. Predatory nematodes can be bred by soaking a specific recipe of leaves and other detritus in water, in a dark, cool place, and can even be purchased as an organic form of pest control. Rotations of plants with nematode resistant species or varieties is one means of managing parasitic nematode infestations. For example, marigolds , grown over one or more seasons (the effect is cumulative), can be used to control nematodes. [ 15 ] Another is treatment with natural antagonists such as the fungus gliocladium roseum . Chitosan is a natural biocontrol that elicits plant defense responses to destroy parasitic cyst nematodes on roots of sobyean, corn, sugar beets, potatoes and tomatoes without harming beneficial nematodes in the soil. [ 16 ] Furthermore soil steaming is an efficient method to kill nematodes before planting crop. CSIRO has found [ 17 ] that there was 13- to 14-fold reduction of nematode population densities in plots having Indian mustard (Brassica juncea) green manure or seed meal in the soil. Hundreds of Caenorhabditis elegans were featured in a research project on NASA's STS-107 space mission (which ended in the Space Shuttle Columbia Disaster ). [ 18 ]
A Guide to characteristics of Class Mammalia The Class Mammalia is well represented in Southern Africa. There are 293 species of land mammals and 37 species of marine mammals in the Southern African subregion. That is 330 of the around 5000 mammal species found on Earth! Class Mammalia -- all mammals share three characteristics not found in other animals: 3 middle ear bones; hair; and the production of milk by modified sweat glands called mammary glands. Mammals hear sounds after they are transmitted from the outside world to their inner ears by a chain of three bones, the malleus, incus, and stapes. Two of these, the malleus and incus, are derived from bones involved in jaw articulation in most other vertebrates. Mammals have hair. Adults of some species lose most of their hair, but hair is present at least during some phase of the ontogeny of all species. Mammalian hair, made of a protein called keratin, serves at least four functions. First, it slows the exchange of heat with the environment (insulation). Second, specialized hairs (whiskers or "vibrissae") have a sensory function, letting the owner know when it is in contact with an object in its external environment. These hairs are often richly innervated and well-supplied with muscles that control their position. Third, through their color and pattern, hairs affect the appearance of a mammal. They may serve to camouflage, to announce the presence of especially good defense systems (for example, the conspicuous color pattern of a skunk is a warning to predators), or to communicate social information (for example, threats, such as the erect hair on the back of a wolf; sex, such as the different colors of male and female capuchin monkeys; presence of danger, such as the white underside of the tail of a whitetailed deer). Fourth, hair provides some protection, either simply by providing an additional protective layer (against abrasion or sunburn, for example) or by taking on the form of dangerous spines that deter predators (porcupines, spiny rats, others). Mammals feed their newborn young with milk, a substance rich in fats and protein that is produced by modified sweat glands called mammary glands. These glands, which take a variety of shapes, are usually located on the ventral surface of females along paths that run from the chest region to the groin. They vary in number from two (one right, one left, as in humans) to a dozen or more. Other characteristics found in most mammals include highly differentiated teeth; teeth are replaced just once during an individual's life (this condition is called diphyodonty, and the first set is called "milk teeth); a lower jaw made up of a single bone, the dentary; four-chambered hearts, a secondary palate separating air and food passages in the mouth; a muscular diaphragm separating thoracic and abdominal cavities; highly developed brain; endothermy and homeothermy; separate sexes with the sex of an embryo being determined by the presence of a Y or 2 X chromosomes; and internal fertilization. The Class Mammalia includes around 5000 species placed in 26 orders (systematists do not yet agree on the exact number or on how some orders are related to others). Mammals can be found in all continents and seas. In part because of their high metabolic rates (associated with homeothermy and endothermy), they often play an ecological role that seems disproportionately large compared to their numerical abundance. Subclass Prototheria - Not represented in southern Africa Order Monotremata -- Monotremes: platypus and echidnas Subclass Metatheria (marsupials) - Not represented in southern Africa Order Didelphimorphia Order Paucituberculata Order Microbiotheria Order Dasyuromorphia Order Peramelemorphia Order Notoryctemorphia Order Diprotodontia Subclass Eutheria (placentals) Order Insectivora -- Insectivores: shrews, moles, hedgehogs, tenrecs, etc. Order Macroscelidea -- elephant shrews Order Scandentia -- tree shrews Order Dermoptera -- colugos Order Chiroptera --bats Order Primates --primates Order Xenarthra -- edentates; sloths, armadillos and anteaters Order Pholidota -- pangolins Order Lagomorpha -- rabbits and pikas Order Rodentia -- rodents Order Cetacea -- whales, dolphins, and porpoises Order Carnivora -- carnivores Order Tubulidentata -- aardvark Order Proboscidea -- elephants Order Hyracoidea -- hyraxes Order Sirenia -- dugongs and manatees Order Perissodactyla -- horses, rhinos, tapirs Order Artiodactyla -- antelope, giraffe, camels, pigs, hippos, etc.
