પ્રાણી સૃષ્ટિનું વર્ગીકરણ

• The animal kingdom exhibits diverse forms and structures.
• Millions of animal species have been identified and classified.
• Classification is crucial for organizing and placing newly discovered species.

Basis of Classification

• Despite structural and morphological differences, animals share fundamental features.
• These features include cell arrangement, body symmetry, coelomic cavity nature, digestive patterns, and circulatory or reproductive systems.
• These characteristics form the basis for animal classification.

Levels of Organization

• Animal kingdom members are multicellular but don't exhibit uniform cell organization.
• Porifera (sponges) have loosely arranged cells (loose cell aggregates) with limited functional coordination, representing a cellular level of organization.
• Coelenterates display a more complex arrangement where cells performing similar functions form tissues (tissue level organization).
• Higher levels of organization, such as in Platyhelminthes, involve tissues forming organs for specific functions (organ level).
• In animal groups like annelids, arthropods, mollusks, echinoderms, and chordates, organs are integrated into functional systems, each dedicated to specific physiological roles (organ system level organization).
• Different animal groups showcase varying complexities in organ systems.
• Platyhelminthes have an incomplete digestive system with a single opening serving as both mouth and anus.
• Complete digestive systems feature separate mouth and anus openings.
• Circulatory systems can be open or closed.
• In open circulatory systems, blood is pumped out of the heart, bathing cells and tissues.
• Closed circulatory systems confine blood within vessels of varying diameters (arteries, veins, capillaries).

Symmetry

• Animals are classified based on symmetry.
• Sponges are asymmetrical, lacking a plane dividing the body into equal halves.
• Radial symmetry occurs when any plane passing through the central axis divides the body into identical halves, seen in coelenterates, ctenophores, and echinoderms.
• Bilateral symmetry divides the animal into two identical left and right halves along a central axis, found in annelids and arthropods.

Diploblastic and Triploblastic Organization

• Diploblastic animals have cells arranged in two embryonic layers: the outer ectoderm and inner endoderm (e.g., coelenterates).
• An undifferentiated layer, mesoglea, exists between the ectoderm and endoderm.
• Triploblastic animals possess a third germinal layer, the mesoderm, between the ectoderm and endoderm (e.g., Platyhelminthes to chordates).

Coelom

• The presence or absence of a cavity between the body wall and digestive tract is significant in classification.
• The coelom is a body cavity lined by mesoderm.
• Coelomate animals possess a coelom (e.g., annelids, mollusks, arthropods, echinoderms, hemichordates, and chordates).
• Pseudocoelomates have a false coelom where the mesoderm is present as scattered pouches between the ectoderm and endoderm (e.g., nematodes).
• Acoelomates lack a coelom (e.g., Platyhelminthes).

Segmentation

• Some animals exhibit metameric segmentation, with bodies externally and internally divided into repetitive segments.
• Earthworms demonstrate this segmentation.
• Metamerism refers to this segmented organization.

Notochord

• The notochord is a rod-like structure derived from mesoderm on the dorsal side during embryonic development in some animals.
• Chordates possess a notochord.
• Non-chordates lack a notochord (e.g., porifera to echinoderms).

Classification of Animals

• The animal kingdom is broadly classified based on common fundamental features.

Porifera

• Porifera are commonly known as sponges.
• Most are marine and asymmetrical.
• They are primitive multicellular organisms with a cellular level of organization.
• Sponges have a water transport or canal system where water enters through ostia into a central cavity (spongocoel) and exits through the osculum.
• This system aids in food gathering, gas exchange, and waste removal.
• Choanocytes line the spongocoel and canals, facilitating intracellular digestion.
• The body is supported by spicules or spongin fibers forming an endoskeleton.
• Sponges are hermaphroditic, producing both ova and sperm.
• They reproduce asexually by fragmentation and sexually by gamete formation.
• Internal fertilization and indirect development through a larval stage occur.
• Scypha, Spongilla (freshwater sponge), and Euspongia (bath sponge) are examples.

Coelenterata (Cnidaria)

• Coelenterates are aquatic, mostly marine, sessile or free-swimming, and radially symmetrical.
• Cnidaria gets its name from cnidoblasts or cnidocytes containing stinging capsules (nematocysts) present on tentacles and the body.
• Cnidoblasts aid in anchorage, defense, and prey capture.
• Coelenterates exhibit tissue-level organization and are diploblastic.
• They have a gastro-vascular cavity with a single opening, the hypostome.
• Digestion is extracellular and intracellular.
• Some coelenterates, like corals, have a skeleton composed of calcium carbonate.
• Cnidarians exhibit two basic body forms: polyp and medusa.
• Polyps are sessile and cylindrical, like Hydra and Adamsia.
• Medusae are umbrella-shaped and free-swimming, like Aurelia (jellyfish).
• Some cnidarians exhibit metagenesis, alternating between polyp and medusa forms, as seen in Obelia.

Ctenophora

• Ctenophores, or comb jellies, are exclusively marine, radially symmetrical, and diploblastic organisms with tissue-level organization.
• The body has eight external rows of ciliated comb plates for locomotion.
• Digestion is both extracellular and intracellular.
• Bioluminescence (light emission by living organisms) is prominent.
• Sexes are not separate; reproduction is only sexual.
• External fertilization and indirect development occur.
• Pleurobrachia and Ctenoplana are examples.

Platyhelminthes (Flatworms)

• Platyhelminthes have dorsoventrally flattened bodies, hence the name flatworms.
• Most are endoparasites found in animals, including humans.
• Flatworms are bilaterally symmetrical, triploblastic, acoelomate, and have organ-level organization.
• Parasitic forms have hooks and suckers for attachment.
• They absorb nutrients directly from the host.
• Flame cells aid in osmoregulation and excretion.
• Sexes are not separate; internal fertilization and development through larval stages occur.
• Planaria exhibits high regeneration capacity.
• Tapeworm (Taenia) and Liver fluke (Fasciola) are examples.

Aschelminthes (Roundworms)

• Aschelminthes have a circular body in cross-section, hence the name roundworms.
• They may be free-living, aquatic, terrestrial, or parasitic.
• Roundworms exhibit organ-system level organization, bilateral symmetry, triploblastic nature, and pseudocoelom.
• The alimentary canal is complete with a muscular pharynx.
• An excretory tube removes wastes through an excretory pore.
• Sexes are separate (dioecious); females are often longer than males.
• Internal fertilization and direct or indirect development occur.
• Ascaris (Roundworm), Wuchereria (Filaria worm), and Ancylostoma (Hookworm) are examples.

Annelida

• Annelids are aquatic (marine and freshwater) or terrestrial, free-living, and sometimes parasitic.
• They exhibit organ-system level organization and bilateral symmetry.
• Annelids are triploblastic, metamerically segmented, and coelomate.
• The body surface is distinctly marked into segments (metameres).
• Longitudinal and circular muscles aid in locomotion.
• Aquatic annelids like Nereis have parapodia for swimming.
• A closed circulatory system is present.
• Nephridia aid in osmoregulation and excretion.
• The nervous system consists of paired ganglia connected by lateral nerves to a double ventral nerve cord.
• Nereis is dioecious, while earthworms and leeches are monoecious.
• Reproduction is sexual.
• Nereis, Pheretima (Earthworm), and Hirudinaria (Leech) are examples.

Arthropoda

• Arthropoda is the largest phylum in the animal kingdom, including insects.
• These organisms have organ-system level organization.
• They are bilaterally symmetrical, triploblastic, segmented, and coelomate.
• The body is covered by a chitinous exoskeleton.
• The body consists of a head, thorax, and abdomen.
• They have jointed appendages.
• Respiratory organs include gills, book gills, book lungs, or the tracheal system.
• An open circulatory system is present.
• Sensory organs include antennae, eyes (compound and simple), statocysts, or balance organs.
• Excretion occurs through Malpighian tubules.
• Mostly dioecious, with internal fertilization and mostly oviparous.
• Development is direct or indirect.
• Economically important insects include Apis (Honey bee), Bombyx (Silkworm), and Laccifer (Lac insect).
• Vectors include Anopheles, Culex, and Aedes.
• Gregarious pests include Locusta (Locust).
• A living fossil is Limulus (King crab).

Mollusca

• Mollusca is the second-largest animal phylum.
• Molluscs are terrestrial or aquatic (marine or freshwater).
• They have organ-system level organization, and are bilaterally symmetrical, triploblastic, and coelomate.
• The body is covered by a calcareous shell and is unsegmented, with a distinct head, muscular foot, and visceral hump.
• A soft, spongy layer of skin (mantle) covers the visceral hump.
• The space between the hump and mantle is the mantle cavity, containing feather-like gills for respiration and excretion.
• The anterior head region has sensory tentacles.
• The mouth contains a rasping organ called the radula.
• Usually dioecious and oviparous with indirect development.
• Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Sea-hare), Dentalium (Tusk shell), and Chaetopleura (Chiton) are examples.

Echinodermata

• Echinodermata have an endoskeleton of calcareous ossicles and are thus called echinoderms.
• All are marine with organ-system level organization.
• Adults are radially symmetrical, but larvae are bilaterally symmetrical.
• They are triploblastic and coelomate.
• The digestive system is complete, with a mouth on the ventral side and an anus on the dorsal side.
• The water vascular system is a distinctive feature aiding in locomotion, food capture, transport, and respiration.
• An excretory system is absent.
• Sexes are separate; reproduction is sexual.
• Fertilization is usually external.
• Development is indirect with free-swimming larvae.
• Asterias (Star fish), Echinus (Sea urchin), Antedon (Sea lily), Cucumaria (Sea cucumber), and Ophiura (Brittle star) are examples.

Hemichordata

• Hemichordata was previously considered a subphylum under Chordata but is now a separate phylum under Non-chordata.
• This phylum includes a small group of worm-like marine animals with organ-system level organization.
• They are bilaterally symmetrical, triploblastic, and coelomate.
• The body is cylindrical and composed of an anterior proboscis, a collar, and a long trunk.
• An open circulatory system is present.
• Respiration occurs through gills.
• The proboscis gland excretes.
• Sexes are separate.
• External fertilization and indirect development occur.
• Balanoglossus and Saccoglossus are examples.

Chordata

• 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 organ-system level organization.
• They possess a post-anal tail and a closed circulatory system.
• Chordates are divided into three subphyla: Urochordata or Tunicata, Cephalochordata, and Vertebrata.
• Urochordata and Cephalochordata are referred to as Protochordates and are exclusively marine.
• In Urochordata, the notochord is present only in the larval tail.
• In Cephalochordata, the notochord extends from head to tail throughout life.
• Ascidia, Salpa, and Doliolum are examples of Urochordata; Branchiostoma (Amphioxus or Lancelet) is an example of Cephalochordata.
• Members of subphylum Vertebrata possess a notochord during the embryonic period; it is replaced by a cartilaginous or bony vertebral column in adults.
• All vertebrates are chordates, but not all chordates are vertebrates.
• Vertebrates have a ventral muscular heart with two-, three-, or four-chambered hearts, kidneys for excretion and osmoregulation, and paired appendages for locomotion.
• The subphylum Vertebrata is further divided.

Cyclostoma

• All living members bind to some fishes as parasites. Body consists of 6-15 holes for respiration.

Chondrichthyes

• Skeleton and mouth are at ventral side. Body covered from scales.

Osteichthyes

• Scales surround body.

Amphibia

• Can live in water and land. It is divided into head and torso. Skin remain slick with mucus.

Reptilia

• Body has reptile behaviour due to scabs.

Aves

• Have wings and teeth, so they can fly.

Mammalia

• Most unique characters.