Objective
To study some selected animals based on their external features.
Theory
Classification of animals

Pic.1- Classification of Animals
EXTERNAL FEATURES OF EACH PHYLUM
PHYLUM PROTOZOA
- Kingdom: Protista
- Phylum: Amoebozoa
- Class: Tubulinea
- Order: Tubulinida
- Family: Amoebidae
- Genus: Amoeba
- Species: Proteus

Pic.2 - Amoeba
Nature of Organism:
- They are known as acellular or non-cellular organism.
- A protozoan body consists of only a protoplasm mass, called acellular or non-cellular animal.
Habitat:
- They are primarily aquatic, either free-living parasitic or commensal.
Cellular Structure:
- A single cell performs all the vital activities; thus, the single cell acts like a whole body.
Body Covering:
- The body of protozoa is either naked or covered by a pellicle.
Locomotion:
- The locomotory organs are pseudopodia (false foot) or cilia or absent.
Digestion:
- The digestion is intracellular and occurs in food vacuoles.
PHYLUM PORIFERA
Kingdom |
Animalia |
Animalia |
Animalia |
Phylum |
Porifera |
Porifera |
Porifera |
Class |
Calcarea |
Demospongia |
Demospongia |
Order |
Leucosolenida |
Dictyoceratida |
Haplosclerida |
Family |
Sycettidae |
Spongiidae |
Spongillidae |
Genus |
Sycon |
Euspongia |
Spongilla |
Species |
Sycon ciliatum |
Spongia officinalis |
Spongilla lacustris |

Pic.3 - Examples of Porifera
Oldest Animal Species:
- Sponges are regarded as one of the oldest animal species.
- They are commonly known as Sponges.
Multicellularity:
- Despite being multicellular, they are among the simplest creatures without any tissues or organs.
Habitat:
- Sponges' close relationship with water requires an aquatic environment to survive.
Dependency on Water:
- Water is crucial for nutrition, gas exchange, and excretion.
Body Structure:
- The bodies of sponges have numerous ostia, also known as pores or holes.
- Sponge body structures enable water to flow through the body, filtering out food and absorbing dissolved oxygen while removing waste.
Lack of Specialized Systems:
- This phylum of organisms lacks specialized neurological, circulatory, or digestive systems.
- Instead, they possess a water transportation or canal system that handles gas exchange, digestion, and excretion.
Body Symmetry:
- The bodies of sponges lack symmetry and have a modified shape to maximize the efficiency of water flow through the inside central hollow.
PHYLUM CNIDARIA
- Kingdom: Animalia
- Phylum: Cnidaria
- Class: Hydrozoa
- Order: Anthoathecata
- Family: Hydridae
- Genus: Hydra
- Species: Hydra vulgaris

Pic.4 - Hydra
Phylum:
- Cnidaria, also known as Coelenterata, comprises a diverse group of aquatic organisms.
Characteristics:
- They are characterized by specialized cells called cnidocytes, containing stinging structures known as nematocysts.
- Radially symmetrical aquatic organisms are primarily found in marine environments.
- They can be either sessile or free-swimming.
Habitat:
- Primarily marine, but some are freshwater.
- Sessile or free-swimming.
Cnidocytes:
- Cnidoblasts or cnidocytes, found on tentacles and the body, give the phylum its name.
- Cnidocytes are used for prey capture, defence, and anchoring.
Body Organization- Tissue-Level Organization
- Cnidarians are diploblastic and exhibit tissue-level organization.
Gastro-Vascular Cavity:
- Single aperture, the mouth, on the hypostome in the centre of the gastro-vascular cavity.
Representative Organisms:
- The phylum includes familiar organisms such as jellyfish, corals, and sea anemones.
Life Cycle:
- Cnidarians exhibit two primary body forms during their life cycle: the polyp and the medusa.
- The polyp form is typically cylindrical, with a mouth surrounded by tentacles facing upward, and it is generally sessile, attaching to substrates like rocks or coral reefs.
- In contrast, the medusa form is bell-shaped and free-swimming, with tentacles hanging down.
- Cnidarians display a unique alternation of generations, where polyps asexually produce medusae, and medusae sexually produce polyps.
Digestion:
- Digestion occurs both within and outside of cells.
Examples:
- Medusa form examples include Aurelia (jellyfish).
- Examples of polyp forms include Hydra, Adamsia, etc.
PHYLUM PLATYHELMINTHES
- Kingdom: Animalia
- Phylum: Platyhelminthes
- Class: Trematoda
- Order: Plagiorchiida
- Family: Fasciolidae
- Genus: Fasciola
- Species: Fasciola hepatica

Pic.5 - Liver fluke
Body Form:
- Flatworms are called so due to their Dorso-ventrally flattened bodies.
Parasitic Nature:
- Most flatworms are endoparasites found in both humans and other animals.
Body Characteristics:
- Flatworms are triploblastic, acoelomate, and bilaterally symmetrical organisms with organ-level organization.
- Parasitic forms often have hooks and suckers.
Nutrient Absorption:
- Some flatworms absorb nutrients directly from the host through the surface of their bodies.
Excretion and Osmoregulation:
- Specialized cells, known as flame cells, aid in excretion and osmoregulation.
Reproductive Features:
- The sexes are not distinct in flatworms.
- Internal fertilization occurs.
- Numerous larval stages are involved in the development process.
Regeneration Ability:
- Planaria, a member of flatworms, is known for its strong ability to regenerate.
PHYLUM ASCHELMINTHES
- Kingdom: Animalia
- Phylum: Nematoda
- Class: Secernentea
- Order: Ascaridida
- Family: Ascarididae
- Genus: Ascaris
- Species: Ascaris lumbricoides

Pic.6 - Roundworm
Body Shape:
- The body of Aschelminthes, known as roundworms, has a round cross-section.
Ecological Diversity:
- Aschelminthes, or roundworms, can be either parasites on plants and animals or free-living in aquatic and terrestrial environments.
Body Organization:
- Roundworms exhibit organ-system level body organization.
- They are triploblastic, pseudocoelomate, and bilaterally symmetrical creatures.
Alimentary Canal:
- The pharynx in roundworms features a fully formed, muscular alimentary canal.
Excretory System:
- An excretory tube transfers bodily waste from the body cavity through the excretory hole.
Reproductive Features:
- Males and females are unique in roundworms as the sexes are separate (dioecious).
- Females are often larger than males.
PHYLUM ANNELIDA
- Kingdom: Animalia
- Phylum: Annelida
- Class: Clitellata
- Order: Haplotaxida
- Family: Megascolecidae
- Genus: Pheretima
- Species: Posthuma

Pic.7 - Earthworm
Ecological Diversity:
- Annelids can be free-living, occasionally parasitic, aquatic (marine and freshwater), or terrestrial.
Body Organization:
- They exhibit bilateral symmetry and organ-system-level body organization.
- Annelids are coelomate animals, triploblastic and metamerically segmented.
Segmentation:
- The phylum name Annelida is derived from the fact that their body surface is divided into segments or metameres.
Muscular System:
- Annelids have circular and longitudinal muscles that aid in movement.
- Aquatic annelids like Nereis have parapodia lateral appendages that aid in swimming.
Circulatory System:
- Annelids have a closed circulation system.
Excretion and Osmoregulation:
- Nephridia, also known as nephridium, aids in excretion and osmoregulation.
Neural System:
- The neural system comprises two double ventral nerve cords and two paired ganglia.
Reproductive Features:
- Earthworms and leeches are monoecious (having both male and female reproductive organs).
- Nereis, an aquatic variety, is dioecious (having separate sexes).
- Reproduction is sexual.
PHYLUM ARTHROPODA
Kingdom |
Animalia |
Animalia |
Phylum |
Arthropoda |
Arthropoda |
Class |
Insecta |
Malacostraca |
Order |
Hymenoptera |
Decapoda |
Family |
Apidae |
Penaeidae |
Genus |
Apis |
Penaeus |
Species |
Mellifera |
Indicus |

Pic.8 - Honey bee

Pic.9 - Prawn
Phylum Characteristics:
- Arthropoda is the largest phylum in Animalia, including insects.
- Arthropods make up more than two-thirds of all identified species on Earth.
- They are organized at the organ-system level.
Body Characteristics:
- Arthropods are segmented, coelomate, bilaterally symmetrical, and triploblastic creatures.
- They have a chitinous exoskeleton covering their bodies.
- The body is divided into the head, thorax, and abdomen, with joined appendages.
Respiratory Organs:
- Respiratory organs can include gills, book gills, book lungs, or a tracheal system.
- They have an open circulatory system.
Sensory Organs:
- Arthropods have sensory organs like antennae, compound eyes, simple eyes, statocysts, and balance organs.
Excretion:
- Malpighian tubules are used for excretion.
Reproductive Features:
- Most arthropods are dioecious (having separate sexes).
- They reproduce through internal fertilization.
Examples:
- Examples of economically significant insects include the honeybee and the silkworm.
PHYLUM MOLLUSCA
- Kingdom: Animalia
- Phylum: Mollusca
- Class: Gastropoda
- Order: Architaenioglossa
- Family: Ampullariidae
- Genus: Pila
- Species: Globosa

Pic.10 - Apple snail
Phylum Characteristics:
- Mollusca is the second-largest animal phylum.
- It has an organ-system level of organization and can be found in terrestrial or aquatic environments (marine or freshwater).
Body Characteristics:
- Molluscs are coelomate, triploblastic, and bilaterally symmetrical creatures.
- The body is unsegmented and covered in a calcareous shell.
- It has a distinct head, a muscular foot, and a visceral hump.
Visceral Hump and Mantle Cavity:
- A spongy skin covers the visceral hump.
- The mantle cavity, between the hump and the mantle, contains gills resembling feathers for respiration and excretion.
Sensory Organs:
- Sensory tentacles are situated in the anterior head region.
Feeding Organ:
- The mouth contains a file-like rasping organ called a radula for feeding.
PHYLUM ECHINODERMATA
- Kingdom: Animalia
- Phylum: Echinodermata
- Class: Asteroidea
- Order: Forcipulatida
- Family: Asteriidae
- Genus: Asterias
- Species: Asterias rubens

Pic.11 - Starfish
Phylum Characteristics:
- Echinodermata is the phylum of animals with an endoskeleton made of calcareous ossicles.
Habitat and Organization:
- Echinoderms are marine animals with an organ-system level of organization.
- Adult echinoderms are radially symmetrical, while larvae are bilaterally symmetrical.
Body Characteristics:
- They are triploblastic and coelomate animals.
- The digestive system is complete, with the mouth on the lower side and the anus on the upper side.
Water Vascular System:
- The most distinctive feature of echinoderms is the presence of a water vascular system or ambulacral system.
- This system aids in locomotion, respiration, capture, and transport of food.
Excretory System and Reproduction:
- Echinoderms do not have an excretory system.
- The sexes in echinoderms are separate.
PHYLUM CHORDATA
Phylum Chordata Characteristics:
- Animals in the phylum Chordata are characterized by the presence of a notochord, a dorsal hollow nerve cord, and paired pharyngeal gill slits.
- They are bilaterally symmetrical, triploblastic, and coelomate with an organ-system level of organization.
- Chordates possess a post-anal tail and a closed circulatory system.
Class Chondrichthyes:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Chondrichthyes
- Order: Lamniformes
- Family: Lamnidae
- Genus: Carcharodon
- Species: Carcharodon carcharias

Pic.12 - Shark
- Chondrichthyes are marine animals with a streamlined body and a cartilaginous endoskeleton.
- The mouth is located ventrally.
- The notochord is persistent throughout life.
- Gill slits are separate and lack an operculum.
- The skin is tough, containing minute placoid scales.
- Teeth are modified placoid scales that are backwardly directed.
- They have powerful jaws.
- Due to the absence of an air bladder, they must swim constantly to avoid sinking.
- The heart is two-chambered.
- Chondrichthyes are cold-blooded animals, lacking the capacity to regulate their body temperature.
- Sexes are separate, with males having pelvic fins bearing claspers.
- They undergo internal fertilization, and many of them are viviparous.
Class Osteichthyes:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Actinopterygii
- Order: Cypriniformes
- Family: Cyprinidae
- Genus: Labeo
- Species: Catla

Pic.13 - Catla
General Characteristics:
- Osteichthyes include both marine and freshwater fishes with a bony endoskeleton.
- Their body is streamlined for efficient swimming.
- The mouth is mostly terminal, located at the anterior end of the body.
Gills and Operculum:
- They have four pairs of gills covered by an operculum on each side of their bodies for efficient oxygen extraction from water.
Skin and Scales:
- The skin is covered with cycloid or ctenoid scales, providing protection.
Air Bladder:
- Osteichthyes possess an air bladder, aiding in buoyancy control.
Circulatory System:
- The heart is two-chambered, consisting of an atrium and a ventricle.
Thermoregulation:
- Osteichthyes are cold-blooded animals, meaning they lack the ability to regulate their body temperature internally.
Reproductive Features:
- Sexes are separate in Osteichthyes.
- Fertilization is usually external, occurring outside the body.
- They are mostly oviparous, with eggs hatching outside the parental body.
Class Amphibia:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Amphibia
- Order: Anura
- Family: Ranidae
- Genus: Rana
- Species: Rana temporaria

Pic.14 - Frog
Habitat and Limbs:
- Amphibians can live in both aquatic and terrestrial habitats.
- Most amphibians have two pairs of limbs.
Body Structure:
- The body is divisible into a head and trunk.
- Some amphibians may have a tail.
Skin Characteristics:
- Amphibian skin is moist and lacks scales.
Sensory Organs:
- Eyes have eyelids.
- A tympanum represents the ear.
Cloaca:
- The alimentary canal, urinary, and reproductive tracts open into a common chamber called the cloaca, which opens to the exterior.
Respiration:
- Respiration occurs through the gills, lungs, and the skin.
Circulatory System:
- The heart is three-chambered, consisting of two auricles and one ventricle.
Thermoregulation:
- Amphibians are cold-blooded animals.
Reproductive Features:
- Sexes are separate.
- Fertilization is external, occurring outside the body.
Class Reptilia:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Reptilia
- Order: Squamata
- Family: Agamidae
- Genus: Calotes
- Species: Calotes versicolor
.

Pic.15 - Garden lizard
Locomotion and Terrestrial Habitat:
- The class name "Reptilia" refers to their creeping or crawling mode of locomotion.
- Reptiles are mostly terrestrial animals.
Skin Characteristics:
- Dry and cornified skin, often with epidermal scales, covers their body.
Ear and Hearing:
- Reptiles do not have external ear openings.
- The tympanum represents the ear.
Limb Presence:
- Limbs are present in reptiles.
Circulatory System:
- The heart is usually three-chambered, but in crocodiles, it is four-chambered.
Thermoregulation:
- Reptiles are poikilothermic, meaning their body temperature varies with the environment.
Class Aves:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Aves
- Order: Columbiformes
- Family: Columbidae
- Genus: Columba
- Species: Columba livia

Pic.16 - Pigeon
Feathers and Flight:
- Aves (birds) are characterized by the presence of feathers, and most can fly, except for flightless birds like the ostrich.
- They possess beaks, and their forelimbs are modified into wings.
Hind Limbs and Scales:
- The hind limbs have scales modified for walking, swimming, or climbing tree branches.
Skin and Endoskeleton:
- The skin is dry without glands, except for the oil gland at the base of the tail.
- The endoskeleton is fully bony, and the long bones are hollow with air cavities.
Digestive System:
- The digestive tract of birds has additional chambers, including the crop and the gizzard.
Circulatory System:
- The heart is completely four-chambered.
Thermoregulation:
- Birds are warm-blooded animals, capable of maintaining a constant body temperature.
Respiration:
- Respiration is by the lungs, and air sacs connected to the lungs supplement respiration.
Reproductive Features:
- Sexes are separate.
- Fertilization is internal.
- Birds are oviparous, and development is direct.
Class Mammalia:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Lagomorpha
- Family: Leporidae
- Genus: Oryctolagus
- Species: cuniculus

Pic.17 - Rabbit
Habitat Diversity:
- Mammals are found in various habitats, including polar ice caps, deserts, mountains, forests, grasslands, and dark caves.
- Some mammals have adapted to fly or live in water.
Mammalian Characteristic:
- The most unique mammalian characteristic is the presence of milk-producing glands (mammary glands) by which the young ones are nourished.
Limb Adaptations:
- Mammals have two limbs adapted for walking, running, climbing, burrowing, swimming, or flying.
Skin Characteristics:
- The skin of mammals is unique in possessing hair.
- External ears or pinnae are present.
Dental Features:
- Different types of teeth are present in the jaw.
Circulatory System:
- The heart is four-chambered.
Respiration:
- Respiration is by the lungs.
Reproductive Features:
- Sexes are separate, and fertilization is internal.
- Mammals are viviparous with few exceptions, and development is direct.
Learning Outcomes
Students understand:
- The classification of the animal kingdom.
- The concept of external features of animals according to their phylum.
- The habitat of specific animals.