Animalia
Original Scanned PDF – View Notes
Important Terms Used in Characters and Classification of Organisms
1. Cellularity
An organism made up of only one cell is called unicellular or acellular. The source gives protozoans as an example.
Organisms made up of many cells are called multicellular or metazoans. The notes state that all animals except protozoans are multicellular.
2. Body Layers
Organisms having two germ layers—outer ectoderm and inner endoderm. Examples in the source include sponges and coelenterates.
Organisms having three germ layers—outer ectoderm, middle mesoderm and inner endoderm.
3. Symmetry
The body can be divided longitudinally and medially into two equal and similar halves. Each half is a mirror image of the other.
A plane passing through the central axis can divide the body into two equal and similar halves from several directions.
The body cannot be divided into two equal halves.
4. Habitat
Animals that live only in water.
Animals that can live both on land and in water. Example: frog.
Animals that live on land. The source further lists:
5. Body Temperature
Animals whose body temperature varies according to the environment.
Animals whose body temperature does not vary according to the environment. The source gives birds and mammals as examples.
6. Nutrition
Taking food in solid form; also described as animal-like nutrition.
Plant-like nutrition.
Feeding on dead organic matter.
The source describes this as feeding on dead organic matter.
Living on another organism and remaining alive at the expense of the host. Examples: tapeworm and liver fluke.
Feeding on animal flesh. Examples: tiger and lion.
Feeding on plants. Examples: cow and cattle.
7. Digestion
Digestion that takes place inside the cell. Examples: Amoeba and Euglena.
Digestion that takes place outside the cell. Examples: Hydra and earthworm.
8. Respiration
Takes place in the presence of oxygen.
Takes place in the absence of oxygen.
9. Reproduction
Reproduction in which sexes are not involved and only one parent takes part.
Reproduction involving male and female sexes in which male and female gametes fuse to form a zygote.
The source distinguishes animals that lay eggs from those that give birth to young ones.
An individual having both male and female reproductive organs.
Male and female reproductive organs occur in separate individuals.
Phylum Porifera
Poros = pore; ferre = to bear.
Characteristics
- They are multicellular organisms with a cellular grade of organization.
- They are generally sessile, meaning attached to the substratum.
- They are exclusively aquatic, mostly marine, and a few are freshwater organisms.
- They are called pore-bearing animals because the body contains numerous small pores. Water enters through pores called ostia and exits through a larger opening called the osculum.
- Nutrition is holozoic with intracellular digestion, with the help of choanocyte cells.
- The water canal system is well developed.
- Special circulatory, respiratory and excretory parts are absent.
- Reproduction occurs both sexually and asexually. The source lists budding, gemmule formation and regeneration among asexual methods.
- They are hermaphrodites.
Classification of Porifera
The notes divide Porifera into three classes on the basis of the chemical nature of spicules.
Calcarea
- Spicules are made of CaCO3.
- Exclusively marine.
- Examples: Sycon, Leucosolenia.
Hexactinellida
- Spicules are made of silica.
- Exclusively marine.
- Examples: Euplectella, Hyalonema.
Demospongia
- The source writes that spicules are made up of fibres.
- Freshwater forms are included.
- Examples: Spongilla, Euspongia.
Phylum Coelenterata
Koilos = hollow; enteron = intestine.
Characteristics
- The body possesses an internal hollow cavity known as the coelenteron.
- They are multicellular organisms with a tissue grade of organization.
- They show radial symmetry and are described in the source in association with sessile forms.
- They are exclusively aquatic, mostly marine, with a few freshwater organisms.
- They are diploblastic, with outer ectoderm and inner endoderm. A non-cellular gelatinous material called mesoglea lies between these layers.
- The mouth is surrounded by short cylindrical tentacles that assist in locomotion, feeding and defence.
- Special circulatory, excretory and respiratory organs are absent.
- Digestion occurs both extracellularly and intracellularly.
- They show polymorphism with an asexual polyp form and a sexual medusa form.
- Reproduction occurs sexually and asexually.
- Alternation between sexual and asexual cycles is called alternation of generations or metagenesis in the source.
Classification of Coelenterata
The notes divide Coelenterata into three classes on the basis of the presence and absence of reproductive forms, polyp and medusa.
Hydrozoa
- Both polyp and medusa forms are present.
- Mostly marine; a few are freshwater.
- Examples: Hydra, Obelia.
Scyphozoa
- Medusa form is dominant; polyp stage is reduced or absent.
- Exclusively marine.
- Example: Aurelia (jelly fish).
Anthozoa
- Only the polyp form is present.
- Exclusively marine.
- Example: Metridium (sea anemone).
Phylum Platyhelminthes
Platy = flat; helminthes = worm.
Characteristics
- The body is dorsoventrally flattened and leaf-like or ribbon-like, so they are called flatworms.
- They are mostly parasitic; some, such as Planaria, are free-living.
- They are triploblastic and bilaterally symmetrical.
- They are acoelomate. The space between the body wall and internal organs is filled with parenchyma.
- Parasitic forms develop adhesive structures such as hooks, spines and suckers that enable attachment to body parts of the host.
- Nutrition is holozoic.
- The digestive system is incomplete and branched or may be absent. The anus is absent.
- Respiratory organs are absent; the source describes respiration as anaerobic.
- Excretion occurs through flame cells or protonephridia; an excretory pore is present at the posterior end.
- The reproductive system is well developed and complex. They are described as hermaphrodite, bisexual or monoecious.
- Fertilization may occur internally by cross- or self-fertilization. The source also mentions parthenogenesis or paedogenesis in parasitic forms.
- The life cycle may be simple or complex and may require one host (monogenetic) or two hosts (digenetic).
Classification of Platyhelminthes
The source divides the phylum into three classes on the basis of habitat and segmentation.
| Feature | Turbellaria | Trematoda | Cestoda |
|---|---|---|---|
| Habit | Free-living aquatic forms | Exclusively parasitic, including ecto- and endoparasites | Exclusively endoparasitic |
| Body | Unsegmented | Unsegmented | Segmented, tape-like body |
| Hooks & suckers | Absent | Suckers present | Hooks and suckers present |
| Life cycle | Simple | Complex; may require one or more hosts | Complex; may require multiple hosts |
| Alimentary canal | Mouth, pharynx and intestine present | Intestine present in the source table | Not emphasized in the supplied table |
| Example | Planaria | Fasciola hepatica (liver fluke) | Taenia solium (tapeworm) |
Phylum Nemathelminthes
Nema = thread; helminthes = worm.
Characteristics
- They are cylindrical, elongated, unsegmented and worm-like.
- They are mostly parasitic and some are free-living in soil and water.
- They are triploblastic.
- They are bilaterally symmetrical.
- Nutrition is holozoic.
- The alimentary canal is complete and straight.
- The notes describe lateral excretory ducts that collect excretory substances.
- They are unisexual or dioecious.
Classification
The notes divide Nemathelminthes into two classes on the basis of presence or absence of the caudal sense organ called a phasmid.
- Phasmids absent.
- Free-living forms.
- Examples written in the source: Dorylaimus and Rotifers.
- Phasmids present.
- Parasitic forms.
- Example: Ascaris.
Phylum Annelida
Annulus = ring; eidos = form.
Characteristics
- They are elongated and metamerically segmented.
- They are mostly aquatic; some are terrestrial and burrowing, while a few are parasites that suck blood from vertebrates.
- They are triploblastic.
- They are bilaterally symmetrical.
- The coelom is a true coelom formed by mesoderm; such a coelom is described as schizocoel in the source.
- Locomotion may occur by setae in earthworm, parapodia in Nereis or suckers in leech.
- Nutrition is holozoic.
- Respiration takes place through the moist body surface by diffusion.
- Excretion takes place through segmentally arranged nephridia.
- The notes state that many are usually hermaphrodites.
Classification of Annelida
The notes divide Annelida into four classes on the basis of locomotory organs.
Polychaeta
- Locomotory organs are parapodia.
- Mainly marine; some freshwater forms.
- Clitellum absent.
- Sexes separate.
- Fertilization external and development indirect.
- Examples: Nereis (clam worm), Amphitrite.
Hirudinea
- Locomotory organs are suckers.
- Mostly freshwater and terrestrial; some marine.
- Mostly ectoparasites with suckers.
- Clitellum is seen only during the breeding season.
- Fertilization is internal and the source notes cocoon formation.
- Example: Hirudinaria.
Oligochaeta
- Locomotory organs are setae, found in each segment.
- Mostly terrestrial; some freshwater.
- Clitellum is present.
- They are hermaphrodite and development is direct.
- Example: Pheretima (earthworm).
Archiannelida
- The source describes segmentation as internal only.
- Exclusively marine.
- No parapodia or setae.
- Tentacles present.
- Sexes separate and development indirect.
- Example: Polygordius.
Phylum Mollusca
Molluscus = soft.
Characteristics
- The body is soft and unsegmented.
- They are mostly freshwater or marine, and a few are terrestrial living in damp places.
- They are triploblastic and bilaterally symmetrical, except in Gastropoda where the source notes body asymmetry.
- A hard, protective, calcareous covering called a shell forms the exoskeleton of the body.
- The body is divisible into head, mantle, visceral mass and foot.
- Sense organs include eyes, tentacles, osphradium (water-testing organ) and statocyst (organ of equilibrium).
- Respiration occurs through ctenidia or gills in aquatic forms and a pulmonary sac in terrestrial forms.
- They are mostly unisexual; the source writes external fertilization.
Classification of Mollusca
The notes divide Mollusca into five classes on the basis of the structure and function of the foot.
Gastropoda
- Foot is generally flat and helps in creeping movement.
- Body is covered by a hard shell.
- Body asymmetry.
- Marine, freshwater and terrestrial forms.
- Examples: Apple snail (Pila), garden snail (Helix).
Scaphopoda
- Foot is generally pointed and helps in burrowing.
- Body is covered by a hard shell.
- Bilateral symmetry.
- Exclusively marine.
- Example: Dentalium.
Pelecypoda
- The foot is described as hatchet-like and helps in burrowing or digging.
- The body is covered by a shell with two valves.
- Bilateral symmetry.
- Example: Unio.
Cephalopoda
- The foot is modified into arms with suckers.
- Bilateral symmetry.
- The source writes “marine & fresh water.”
- Examples: Octopus, Sepia.
Amphineura
- Foot is generally flat and helps during creeping.
- Bilateral symmetry.
- The source again writes marine and freshwater habitat.
- Example: Chiton.
Phylum Echinodermata
Echinos = spine; derma = skin.
Characteristics
- The body is covered with spines.
- They are exclusively marine; the source notes that they are not found in Nepal.
- The body is triploblastic and radially symmetrical.
- The head is not distinct; the body is divided into oral and aboral surfaces.
- Locomotion occurs with the help of tube feet.
- The water vascular system is an important characteristic and helps in circulation, respiration, feeding and excretion.
- Excretory organs are absent.
- They are unisexual.
Classification of Echinodermata
The source classifies the phylum on the basis of the number and type of arms and the form of the body. Its diagram shows the subphyla Eleutherozoa and Pelmatozoa, with five classes in total.
Asteroidea
- Body star-shaped with five radiating arms not distinctly separated from the central disc.
- Oral and aboral surfaces are distinct.
- Example: Asterias (starfish).
Ophiuroidea
- Body star-shaped with five radiating arms distinctly separated from the central disc.
- Ambulacral grooves are absent or covered with ossicles in the source.
- Example: Ophiocoma.
Echinoidea
- Body generally circular without arms.
- Ambulacral grooves are covered with ossicles.
- Example: Echinus.
Holothuroidea
- Body generally elongated, without arms and spines.
- Mouth is surrounded by tentacles.
- Example: Holothuria (sea cucumber).
Crinoidea
- The source describes a more or less circular body with arms.
- Ambulacral grooves and scattered ossicles are mentioned.
- Example: Antedon.
Phylum Chordata
Characteristics
- A notochord is present at some stage of development.
- A dorsal tubular nerve cord is present.
- Gill slits or gill openings occur on either side of the pharynx at some stage of development.
- A well-developed coelom is present.
- The heart is situated ventrally.
Three Important Characters of Chordata
Notochord
Noton = back; chorda = cord.
The notochord is described as a stiff, solid, rod-like structure providing internal support. It lies between the nerve cord and alimentary canal and is present either in the embryonic stage or throughout life. The source states that later it may be replaced in the adult by an ossified vertebral column or backbone.
Nerve Cord
It is tubular nervous tissue situated dorsally above the notochord. The source states that later it develops into central nervous tissue, namely the brain and spinal cord.
Gill Slits
These are paired lateral gill openings on both sides of the pharynx and are respiratory openings taking part in gaseous exchange. The notes state that they remain throughout life in fishes and are seen only during the embryonic stage in higher vertebrates.
Classification Shown in the Source
The handwritten chart on page 11 shows four main labels under Chordata:
The lower part of the same handwritten chart additionally shows the labels Agnatha, Gnathostomata, Pisces, Tetrapoda, Amphibia, Reptilia, Aves and Mammalia.
Discussion
Share a helpful question, idea, or explanation with other students.