Biodiversity and classification of Living Organisms: Key Facts and Insights

Objectives

This blog post provides readers with the following objectives. The reader will be able to:

o   State the importance of classification of living organism.

o   Outline the general characteristics of the five kingdoms of living things.

o   Identify and classify organisms into their respective kingdoms.

o   List the characteristics of major Phyla of Kingdoms Protoctista and Fungi.

o  Describe the characteristics of the major divisions and classes of Kingdom Plantae

o   Outline the major phyla and classes of Kingdom Animalia.

o   Describe the characteristics of the major phyla and classes of Kingdom Animalia.

o   Describe the characteristics of the major orders of Class Insecta.

o   Construct identification keys using characteristics of organisms.

Classification of Living Things

Biological classification is the sorting and grouping of living things according to their common characteristics. Biologists place organisms into groups known as taxa (singular: taxon), based on their characteristics. This branch of biology is referred to as taxonomy. Taxonomy is the study of classification of organism.

Early Taxonomist

• Aristotle (Greece, 384–322BC)aGreek philosopher was the first to classify organisms. His system of classification was based on mainly appearances. He classified plants as herbs, trees and shrubs based on their size. He classified animals according to where they lived and structural similarities.Aristotle also classified animals whether they have red blood or not. Aristotle’s classification was used for nearly 2,000 years. 

• John Ray (England, 1627–1705) He classified plants according to similarities and differences. He was the first biologist to introduce the concept of species. He defined species as a group of similar individuals that can interbreed and produce fertile offspring.

• Carolus Linnaeus (1707-1778) a Swedish botanist. Linnaeus system of classification was widely accepted and is still the basic framework for all taxonomy.  His system of classification is called Binomial system. He used two Latin words to describe each species of organism (known to as scientific name). The first name shows the genus, whilst the second name shows the species which the organism belongs. The genus name starts with capital letter and species starts with a small letter. Both names must be underlined separately when hand written or should be in italic when typed.

Therefore; binomial nomenclature is a system of naming organism using two-part name.

Classification of organisms is hierarchical. There are seven main ranks (taxa) into which organisms are placed: Kingdom, Phylum/Division, Class, Order, Family, Genus and Species.

Classification of Some Living Organisms

Taxon	Domestic Dog	Human	Maize
Kingdom	Animalia	Animalia	Plantae
Phylum/Division	Chordata	Chordata	Angiospermophyta
Class	Mammalia	Mammalia	Monocotyledoneae
Order	Carnivora	Primates	Graminales
Family	Canidae	Hominidae	Graminaceae
Genus	Canis	Homo	Zea
Species	Familaris	Sapien	May

Importance of Classification

• It enables scientists to communicate easily with one another.
• It shows similarities and relationships among organisms.
• It reveals evolutionary trends in different groups.
• It enables easy identification and study of organisms.
• It helps scientists in their research work such as identifying new varieties of organism when they arise. 
• It avoids confusion associated with common name
• It shows geographical distribution of organisms

The Five Kingdom and Hierarchy of Classification

Classification puts all organisms into five groups:

1. Kingdom Prokaryotes (bacteria)
2. Kingdom Protoctista (protozoa and algae)
3. Kingdom Fungi (fungi)
4. Kingdom Plantae (plants)
5. Kingdom Animalia (animals)

Kingdom: Prokaryotae or Monera

Examples: Bacteria, Blue-green algae (cyanobacteria), and Spirochetes

General Characteristics of Prokaryotes       

1. unicellular organisms
2. no definite nucleus
3. no nuclear membrane
4. lack membrane-bound organelles
5. photosynthetic, chemosynthetic, or feed by absorption
6. the cell is usually surrounded by capsule or mucilage
7. reproduction is mainly by binary fission (asexual reproduction)

False Colour Electron micrograph of a colony of Bacillus cereus

Kingdom: Protoctista

General Characteristics

• eukaryotic (true nucleus) and microscopic
• mostly unicellular but few are multicellular
• membrane bound organelles
• absence of tissues or organs
• some are photoautotrophs, others ingest food (heterotrophs) or (saprotrophs)
• some are both autotrophs and heterotrophs (called mixotrophs)

There are several phyla under kingdom protoctista, which includes the following;

Phylum: Chlorophyta (Green algae)

Examples: Chlamydomonas, Volvox, Spirogyra

Characteristics of Chlorophytes 

• live in either fresh water, marine or damp soil
• single-celled, colonial, filamentous, or multicellular
• the cell wall contains cellulose
• presence of chlorophylls and are photosynthetic
• food is store as starch inside the chloroplast
• some possess flagella

Phylum: Rhizopoda

Examples: Amoeba proteus, Entamoeba histolytica

Characteristics of Rhizopoda 

• found in damp soil, marine, and freshwater
• unicellular, few multicellular
• movement is by cytoplasmic extensions called pseudopodia
• feed by phagocytosis or engulfing of prey
• reproduce asexually by fission

Phylum: Rhodophyta (Red algae)

Examples: Glacillaria, Galaxaura, plumaria

Characteristics of Rhodophytes 

• mainly found in marine waters
• mostly multicellular
• red color is due to red photosynthetic pigment
• the pigments are able to absorb blue and green light
• cell walls contain cellulose and agar (used as a base in culture dishes to grow microbes)  

Phylum: Phaeophyta (Brown algae)

Examples: Fucus, Sargassam, Laminaria

Characteristics of Phaeophytes 

• multicellular found in marine habitat
• brown algae are photosynthetic
• brown color is due to carotenoid pigments
• the body (thallus) contains holdfasts for attachment

Phylum: Ciliophora (Ciliates)

Example: Paramecium, Vorticella, Didinium

Characteristics of Ciliophorans 

• marine and freshwater organisms
• unicellular organisms
• the pellicle is covered with numerous of cilia
• presence of large macronucleus and a smaller micronucleus
• reproduction involves both sexual and asexual means

Phylum: Apicomplexa (Sporozoans)

Examples: Plasmodium, Toxoplasma

Characteristics of Sporozoans

• Unicellular
• non-motile
• mainly parasitic
• reproduction is by sexual and asexual
• the apex of the cell contains a complex organelles used to penetrate host cell

Phylum: Euglenophyta (Euglenozoans)

Examples: Euglena

Characteristics of Euglenophytes 

• they are Unicellular organisms
• they are mixotrophs (photosynthetic and heterotrophic)
• possess chlorophyll and carotenoids
• presence of flagella for movement
• possess eyespot for detecting the presence of light
• reproduction is asexual

Phylum: Oomycota (Slime mould)

Characteristics of Oomycotes 

• found in damp habitat
• they are free cells or multinucleated aggregate
• possess non-septate hyphae
• they are biflagellate
• reproduced by asexual and sexual means.

Phylum: Zoomastigophora (Flagellates)

Examples: Trypanosoma, Trichomonas, Giardia

Characteristics of Zoomastigophora 

• they are flagellated, unicellular
• Mode of feeding is heterotrophic; ingesting and absorbing food
• their reproduction is asexual
• mostly parasitic, living in the gut of animal hosts

Kingdom: Fungi

General Characteristics of Fungi

• mostly multicellular, few single-celled (e.g. yeasts)
• they are eukaryotes
• no chlorophyll (heterotrophs)
• non-motile
• most are saprotrophic, parasitic and others are mutualistic
• have cell walls are made of chitin
• vegetative body is made up hyphae (singular: hypha)
• hyphae may have internal cross walls, called septa, or lack cross walls, aseptate.

The phyla of kingdom fungi include:

Phylum: Zygomycota (Zygomycetes)

Examples: Rhizopus, Mucor

Characteristics of of Zygomycetes

• terrestrial
• rhizoids anchor the organism, release digestive enzymes and absorb food 
• usually, saprotrophs but some are parasitic
• hyphae are aseptate or non-septate (lack cross wall)
• reproduction is by both sexual and asexual means
• asexual reproductive structure called sporangium, produces sporangiospores

Bread mould

Phylum: Ascomycota (Sac fungi)

Examples: Yeasts, Molds, Morels, Truffles and many plant pathogens

Characteristics of Ascomycetes

• the body consists of septate hyphae
• reproduce both sexually and asexually
• asexual spores called conidia form on the tips of a hyphae called condiophores
• hyphae (ascocarp) produce sexual spores called ascospores enclosed in a sac (ascus)

Phylum: Basidiomycota (Club Fungi)

Examples: Mushrooms, Toadstools, Bracket Fungi, Shelf Fungi, Puffballs, Rusts, Smuts

Characteristics of of Basidiomycetes 

• mostly terrestrial
• saprophytic or parasitic
• the body consist of septa hyphae
• basidium is sexual reproductive structure that produce spores called basidiospores
• some are used as food (mushroom) and others cause crop disease (rusts & smuts)

Kingdom: Plantae

General Characteristics

• multicellular organisms
• have true nucleus (eukaryotic) 
• have cellulose cell walls
• presence of chlorophyll and carotenoid pigments for photosynthesis
• store reserve food as starch  
• they are non-motile

Division: Bryophyta

Examples: Mosses, Liverworts, Hornworts

Characteristics of Bryophytes

• found in damp terrestrial habitats or in fresh water
• no vascular tissues
• absence of true roots, stems, or leaves
• rhizoids are root-like structures that absorb water and nutrients
• restricted to moist areas because the flagellated sperms require water to swim to the egg
• the sporophyte is dependent on the gametophyte

There are two classes under division bryophytes:

Class Musci (Mosses)

Example: Funaria and Sphagnum

Characteristics of Mosses

• spirally arranged leaf-like structures
• the sporophyte consists of a foot, a stalk and a capsule containing spores
• spores germinate into horizontal filaments called protonema
• protonema give rise to upright gametophyte and rhizoids
• rhizoids are multicellular

Class Hepaticae (Liverworts)

Example: Marchantia, Pellia

Characteristics of Liverworts

• sporophytes are small and produce windblown spores
• the gametophyte is thalloid (flattened)
• single-celled rhizoids
• the thallus produces cup-shaped structures called Gemma cups containing Gemma cells

Division: Filicinophyta

Examples: Horsetails, Ferns, Whisk ferns

Characteristics of Filicinophyta

• terrestrial plants with vascular tissues
• possesses true roots, stems and leaves
• no seed
• large compound leaves called fronds
• leaves bear sori (singular: sorus) at the underside
• leaves are megaphyllous
• gametophyte is small and heart-shaped
• the gametophyte and sporophyte are independent
• the sperm are flagellated and require water for reproduction

Division: Lycopodiophyta

Examples: Club mosses, Spike mosses, Quillwort

Characteristics Lycopodiophytes

• Terrestrial
• dispersed by windblown spores
• true roots, stems, and spirally arranged leaves
• the stems are horizontal with upright branches
• leaves are microphyllous
• the gametophyte and sporophyte are independent
• limited to moist areas because the flagellated sperms require water for reproduction

Division: Coniferophyta (Conifers)

Examples: pine, cedar and redwood trees. Conifers are the largest group of gymnosperms.

Characteristics Coniferophytes 

• non-flowering, non-fruit, vascular plants with true roots, stem and leaves
• naked seeds are produced in cones
• leaves are needle-like and are adapted for dry conditions
• reproduction in pine
• heterosporous

Division: Cycadophyta (Cycads)

Characteristics of Cycadophytes 

• cone-bearing palm-like plants
• long compound leaves clustered at the apex of short unbranched stem
• non-flowering plants and produce naked seeds
• vascular plants with true roots, stems, and leaves

Division: Angiospermophyta

Characteristics of Angiospermophytes

• the largest group of plants
• the seeds are covered by a fruit
• sporophyte is dominant and heterosporus
• sexual reproduction is by flowers

There are two main classes:

1. Class: Monocotyledonae (Monocotyledon)

E.g., Cereals (maize, barley, oats, rice or wheat), grasses, onion, palms, plantain, bamboo etc.

2. Class: Dicotyledonae (Dicotyledon)

E.g., Silk cotton, pepper, tomato, mango, orange, sunflower, flamboyant, yam etc.

Characteristics of Monocotyledon and Dicotyledon

Dicotyledon	Monocotyledon
Vascular bundles have cambium	Vascular bundles lack cambium
Flower parts in multiples of four or five	Flower parts in multiples of three
Net-veined leaves	Parallel-veined leaves
Vascular bundles are arranged in rings	Vascular bundles are scattered
Two cotyledons (seed leaves)	One cotyledon
Absence of leaf sheath	Presence of leaf sheath
Possess tap root system	Possess fibrous root system
Vascular bundles are few in numbers	Vascular bundles numerous
Leaves are usually narrow, thin and long	Leaves are broad, simple or compound

Kingdom: Animalia

General Characteristics of Animals

• Multicellular
• true nucleus (eukaryotic) 
• Heterotroph
• nervous system for coordination
• motile

Phylum: Porifera (Sponges)

Examples: Leucosolenia, Euplectella

Characteristics of Porifera

• multicellular, lacking specialized tissues and organs
• asymmetrical
• the body is supported by spicules
• diploblastic (ectoderm and endoderm)
• absence of mouth, digestive cavity and anus
• absence of nervous system and sense organs
• reproduction is both by sexual or asexual means

Phylum Cnidaria (Cnidarians or Coelenterates)

Examples: Hydra, Jellyfishes, Corals, Sea anemones, Obelia.

Characteristics of Cnidarians 

• mostly marine, few freshwater (e.g. hydra)
• radial symmetry
• diploblastic (two tissue layers)
• hydrostatic skeleton
• they possess a gut with a single opening
• two tissue layers are separated by mesoglea (non-living gelatinous material)
• presence of long structures called tentacles used to capture prey
• the tentacles contain defense stinging cells called cnidoblast or nematoblast which discharges to trap or sting the prey. 

Phylum: Platyhelminthes (Flatworms)

Examples: Planaria, Tapeworms

Characteristics of Platyhelminthes

• Unsegmented
• bilaterally symmetrical
• triploblastic i.e. having three germ layers
• body is dorso-ventrally flattened
• body has a definite anterior end with a concentration of nerve cells
• acoelomate; contains no internal cavity
• excretory organ (protonephridia with flame cells)
• circulatory and respiratory system are absent
• most are hermaphrodites

Classes of Platyhelminthes: Turbellaria, Trematoda, and Cestoda.

Class: Turbellaria
Example: Planaria

Characteristics of Turbellarians

• free living or commensal with larger animals
• mostly marine
• outer surface covered with cilia for locomotion
• absence of sucker

Class: Trematoda
Examples: Liver fluke (Fasciola hepatica), Blood Fluke (Schistosoma)

Characteristics of Trematodes

• unciliated in the adult stage
• endoparasites
• possess tick cuticle with spines for locomotion
• presences of suckers for attachment to host

Class: Cestoda (Tapeworms)
Examples: Taenia saginatus, Taenia solium

Characteristics of Cestodes 

• endoparasites
• no digestive system but absorbs digested nutrients from host
• no external cilia
• tick cuticle to withstand host digestive enzymes
• body consists of a head (scolex) with suckers and hooks for attachment to host
• presence of reproductive segments called proglottids behind the scolex
• hermaphrodites; the proglottids contain both male and female reproductive organs.

Phylum: Nematoda (Roundworms)

Examples; Ascaris, Trichinella, Dracunculus, Hookworms and Pinworms

Characteristics of Nematodes

• triploblastic
• bilaterally symmetrical
• pseudocoelomate
• cylindrical and not segmented
• the body is covered by a tough cuticle
• elongated body tapering at both ends
• possess long unbranched gut with mouth and anus
• free living or parasitic

Dracunculus medinensis, commonly known as Guinea worm.

Phylum: Annelida (Annelid worms or segmented worms)

Characteristics of Annelids

• metameric segmentation, with a round, elongated body
• bilaterally symmetrical
• lack jointed appendages
• tiny chitinous jaws (scolecodonts)
• segmentally arranged ciliated tubules called nephridia, for excretion
• bristle-like structures called chaetae for locomotion

Class: Polychaeta (Marine worms)
Examples: Nereis (rag worm), Arenicola (lugworm)

Characteristics of Polychaetes 

• Marine
• distinct head
• numerous pair of chaetae
• chaetae protrude on lateral projections called parapodia
• no clitellum and do not produce cocoon

Bristle worm.

Class: Oligochaeta (Earthworms)
Examples: Lumbricus, hyperiodrilus, libiodrilus

Characteristics of Oligochaetes

• freshwater worms or earthworms
• no distinct head with few chaetae
• no parapodia
• hermaphroditic
• clitellum present (specialized cocoon secreting region)

Earthworm.

Class: Hirudinea (Leeches)
Example: Hirudo (Medical leech)

Characteristics of Leeches

• ectoparasitic
• no distinct head, no chaetae or parapodia
• have no clitellum
• few body segments

Leech.

Phylum: Mollusca

Examples: Clams, Snails and Cephalopods

Characteristics of Molluscs

• oree living aquatic forms (freshwater or marine), some amphibious
• bilaterally symmetrical
  
• body is soft and unsegmented except monoplacophora
• coelom is reduced to a pericardial cavity around the heart
• body differentiated into three regions - head, visceral hump and foot
• visceral hump is covered by a thin, fleshy fold called mantle
• mantle secretes a calcarious shell, which may be external or internal
• presence of toothed tongue, the radula, composed of chitin
• reproduction is sexual (either unisexual or bisexual)

Class: Gastropoda

Examples: Snails, periwinkles, abalone, slugs

Characteristics of Gastropods

• both salt and fresh water and on land
• the largest group of mollusks
• distinct head with sensory tentacles
• possess either a single shell or no shell
• foot is muscular

Snail.

Class: Cephalopoda (the “head-foots”)

Examples: Nautilus, Squid, Octopus

Characteristics of Cephalopods

• all marine
• large head with conspicuous eyes
• mouth surrounded by tentacles bearing suckers
• shell is internal in squid but absent in octopus
• radula and horny beak or jaws for feeding

Octopus.

Class: Pelecypoda or Bivalvia

Examples: Clams, Oysters, Scallops, Mussels

Characteristics of Pelecypods

• the shell is made up of two equal valves
• have no radula
• lack defined head with no tentacles
• foot is present but laterally compressed
• sessile and sedentary
• filter feeder

Phylum: Arthropoda (Arthropods)

The largest phylum in the animal kingdom

Characteristics of Arthropods

• bilateral symmetrical
• coelomate
• three segmented bodies; the head, thorax, and abdomen
• the head and thorax may be fused to form a cephalothorax
• chitinous exoskeleton
• shed their exoskeleton
• jointed appendages
• ventral nerve chord

Classes of arthropods include;

Class: Arachnida

Examples: Spiders, Scorpions, Mites, Ticks

Characteristics of Arachnids

• Terrestrial
• the body is fused intoacephalothoraxorprosomaandabdomenoropisthosoma
• the cephalothorax bears four pairs of walking legs
• only simple eyes
• absence of antennae
• presence of pedipalps; second pair of appendages, used for feeding
• respiration occurs through book lungs
• have poison glands

Scorpion.

Class: Diplopoda (Millipedes)

Characteristics of Diplopods 

• terrestrial and mainly herbivorous
• elongated cylindrical body with numerous segments
• a pair of antennae and 3 pairs of mouthparts
• absence of poisonous jaws
• two pairs of legs on each segment
• slow-moving and nonaggressive scavenger

Class: Chilopoda (Centipedes)

Characteristics of Chilopods

• terrestrial
• fast-moving carnivores
• body is dorso-ventrally flattened
• two body divisions; a distinct head and elongated trunk
• head bears one pair of poison jaws and a pair antenna
• each body segment has one pair of walking legs

Class: Crustacea (Crustaceans)

Examples: lobsters, crayfish, and crabs), prawn, copepods and krill, barnacles

Characteristics of Crustaceans

• mostly aquatic
• the head and thorax are fused into a cephalothorax
• possess pair of compound eyes
• two pairs of antennae
• five pairs of legs on the cephalothorax
• body is covered with calcified (calcium) exoskeleton (carapace)

   

Class: Insecta (Insects)

Characteristics of Insects

• found in all habitat both aquatic and terrestrial
• three segmented bodies; the head, thorax, and abdomen
• the thorax is divided into three segments; prothorax, mesothorax and metathorax
• three pairs of legs and many have one or two pairs of wings
• presence a pair of antennae
• both simple and compound eyes
• Malpighian tubules are excretory organs for removing nitrogenous wastes

Some orders of class Insecta are

Order: Coleoptera

Examples: Beetles and Weevils

• chewing mouthparts (located at the tip of a beak or snout)
• have a hard, dense exoskeleton that covers and protects the body
• the fore wings, known as elytra, are hard and form protective covers over the hind wings

Order: Diptera

Examples: Mosquito, Housefly, Tsetsefly

• piercing or sucking mouthparts
• one pair membranous forewing
• hind wings are reduced to form halteres
• metamorphosis is complete

Order: Hemiptera (bugs)

Examples: Bedbugs, Cotton Stainer, Aphids, Whiteflies

• piercing and sucking mouthparts
• hindwings are membraneous
• forewings are basal half hardened and tough with outer half membraneous
• metamorphosis is incomplete

Order: Isoptera

Examples: Termites

• primarily tropical; nest in ground
• antennae beaded and straight
• chewing mouthparts
• social insects with workers and soldiers
• metamorphosis is incomplete

Order: Hymenoptera

Examples: Ants, Bees and Wasps

• narrow waist between thorax and abdomen
• forewings are larger than hind wings
• forewings are joined to the hind wings by series of hooks
• many species are social insects
• metamorphosis is complete

Order: Lepidoptera

Examples: Butterfly and Moth

• body and wings are covered with powdery scales
• maxillae modified into long proboscis for sucking liquids
• proboscis curled when not in use
• metamorphosis is complete

Order: Odonata

Examples: Dragonflies and Damselflies

• large compound eyes
• very elongate thin thorax and abdomen
• long legs and narrow membranous wings
• often brightly colored
• incomplete metamorphosis

Order: Dictyoptera       

Examples: Cockroaches, Praying mantis

• biting and chewing mouthparts
• forewings are tough (tegmina) and covers membranous hind wings
• forelimbs are modified for grasping
• metamorphosis is incomplete

Order: Orthoptera

Examples: Grasshoppers, Crickets, Locust

• herbivores common in vegetation
• forewings are elongated and thickened
• pronotum "collar" of thorax
• legs modified for jumping or running
• structure to make and receive sound
• metamorphosis is incomplete

Phylum: Echinodermata (Echinoderms)

Examples: Sea stars (starfishes), Sea urchins, Sea cucumbers

Characteristics of Echinoderms

• all are marine
• radially symmetrical but larva is bilaterally symmetrical
  
• body has five-part organization
• possess tube feet with five suckers
• possess an internal skeleton
• contain separately sexes and carry out external fertilization
• able to regenerate lost body parts

For more detailed information on echinoderms, you can explore these resources: Echinodermata: An Overview

Classes of echinoderms include;

Class: Stelleroidea or Asteroidea (Sea Stars)

Examples: Starfishes, Brittle stars

Characteristics of Stelleroidea 

• dorso-ventrally flattened
• star shaped with five arms radiating from the central disc

Class: Echinoidea (Sea Urchins, Sand Dollars)

Characteristics of Echinoidea

• have globular, heart shaped or flattened body with long spines
• lack arms
• have calcareous plates in body wall

Phylum: Chordata (Chordates)

General characteristics of Chordates

• triploblastic, bilateral symmetry, coelomate
• presence of segmented muscle blocks (myotomes)
• a dorsal, hollow nerve cord (spinal cord)
• a dorsal supporting rod called a notochord; (this is replaced by a vertebral column in vertebrates)
• the body is covered by scales, feathers or hairs
• respiration is by means gills or lungs
• presence of post anal tail

Classes of Chordates include;

Class: Chondrichthyes (Cartilaginous Fish)

Examples: Sharks, Dogfishes, Skates, Rays

Characteristics of Chondrichthyes 

• Marine
• fertilization is internal
• absence of operculum
• mouth is ventral
• tail is heterocercal
• endoskeleton composed of cartilage
• body is covered with small tooth like or placoid scales
• absence a swim bladder but have oil-storing capacity for buoyancy
• fast-swimming predators or filter feeders

  

Class: Osteichthyes (bony fish)

E.g.: Tilapia, Goldfish, Tuna, Salmon

Characteristics of Osteichthyes 

• skeleton made of bones
• gills are covered by opercula
• mouth is terminal
• tail is homocercal
• a swim bladder used for buoyancy
• fins supported by rays
• skin is covered by overlapping scales
• Presence of lateral line

Class: Amphibia (Amphibians)

E.g.: Frogs, Toad, Salamanders, Newts

Characteristics of Amphibians

• both aquatic and terrestrial
• thin loose, moist skin with no scales
• mostly tetrapods (four limbs)
• lungs and moist skin are used for gaseous exchange
• reproduce in water because sperm require water to swim
• larva is aquatic but adult adopts an amphibious lifestyle
• larvae (tadpoles) use gills for respiration
• poikilothermic or cold-blooded 

Class: Reptilia (Reptiles)

E.g.: Lizards, Snakes, Turtles, Crocodilians

Characteristics of Reptiles

• pentadactyl limbs with clawed digit except snakes
• homodont dentition
• no external ear and possess bony skeleton
• body covered with dry horny scales
• respiration is through lungs
• fertilization is internal
• lay eggs with leathery shells
• ectothermic or cold blooded

Class: Aves (Birds)

E.g.: Duck, Vulture, Chicken (Domestic fowl), Weaver bird

Characteristics of Birds 

• forelimbs are modified into wings
• presences of feathers  
• presence of strong beak
• enlarged breastbone for attachment of flight muscles
• the eggs have calcareous shells
• absent of teeth and jaws
• horny scales on legs
• endothermic or warm blooded

Class: Mammalia (Mammals)

E.g.: Human, Cat, Cow, Whale, bat, Dolphin

Characteristics of Mammals

oskin is covered with fur or hair

• presence of mammary glands
• possession of external ears or pinnae
• four-chambered heart
• presence of sweat glands
• different kinds of teeth in mouth
• brain is well developed
• reproduction is viviparous (bring forth young alive)
• fertilization is internal 
• endothermic or homeothermic

Subclass: Prototheria/Monotremata (Monotremes)

E.g: Duck billed platypus, Spiny anteater

• lay eggs which the female incubates
• absence of nipples; milk is secreted to the surface of the skin

Subclass: Metatheria/Marsupiala (Marsupials)

E.g.: Kangaroos, Koalas, Opossums

• the young are born immature and crawl into the mother's marsupium (pouch)
• in the pouch it feeds, grows and develops

Subclass: Eutheria (True mammals or Placental Mammals)

E.g.: human, Goats, Sheep, Horses, Pigs, Cats, Dogs

• well-developed placenta for nutrient and waste exchange
• they give birth to a fully developed live young

Identifying organisms using biological keys

This post describes the diversity of living things and shows how they can be classified according to unique characteristics. These characteristics can be used to help to identify organisms. For example, if we find an organism with jointed legs identify it as an arthropod. If it has three body divisions, we know it is an insect and if it has only one pair of wings we know it belongs to the order Diptera. In this way we can narrow down the species it could be until we eventually fully identify the organism. 

Types of keys 

Keys are used for quick and accurate identification of organisms. Fig 1 below shows two types of keys: a branching or dichotomous key and a numbered key, from which the organisms in Fig. 2 can be identified. 

Constructing identification keys 

In order to construct a dichotomous key, the organisms are separated into successive pairs of groups on the basis of clearly observable external features. The ultimate identification is based on distinguishing features that are possessed by only one organism. Dichotomous keys take up space, particularly if many organisms are involved. In this case, a numbered key is better. 

Use this key to identify the organisms showing below 

1. Hard outer covering (shell)                          go to  2 

    No Hard outer covering                               go to 3 

2. Coiled shell                                                    d 

    Flat shell                                                         e 

3. Walking legs                                                go to 4 

    Walking legs                                                c 

4. four pair of walking legs                              a 

    More than four pair of walking legs            b

Click Here for WAEC/ SSCE/ WASSCE/ NOVDEC BIOLGY PAST QUESTIONS AND ANSWERS on Diversity of Living Things

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