પ્રાણી સૃષ્ટિ: વર્ગીકરણ અને સંસ્થાઓ

• These notes cover the animal kingdom.
• It explains animal classification, organization, symmetry, and germ layers.
• It further examines key animal phyla.

Basis of Classification

• Animals have diverse structures and forms.
• Classification is important for organizing the millions of identified species.
• It helps place newly discovered species appropriately.
• Key characteristics for classification include:
  • Cell arrangement
  • Body symmetry
  • Coelom nature
  • Digestive, circulatory, and reproductive systems

Levels of Organisation

• Animal kingdom members are multicellular but don't all have the same cell organization.
• Porifera (sponges) have loosely arranged cells (cellular level organization).
• Cells in sponges are not tightly connected.
• Coelenterates have a more complex arrangement.
• Cells performing similar functions form tissues (tissue level organization).
• Higher levels organize tissues into organs (organ level organization).
• Examples include Platyhelminthes and other higher phyla.
• Organ systems perform specific physiological functions (organ system level organization).
• Different animal groups exhibit varying complexities in organ systems.
• Incomplete digestive systems have a single opening, while complete systems have separate mouth and anus openings.
• Circulatory systems can be open or closed.
  • Open systems pump blood out of the heart, bathing cells and tissues.
  • Closed systems circulate blood through vessels of varying diameters (arteries, veins, capillaries).

Symmetry

• Animals are classified based on symmetry.
• Sponges are typically asymmetrical, lacking a plane that divides them into equal halves.
• Radial symmetry: body can be divided into identical halves through any plane passing through the central axis.
  • Seen in coelenterates, ctenophores, and echinoderms.
• Bilateral symmetry: body can be divided into identical left and right halves along one plane.
  • Observed in annelids and arthropods.

Diploblastic and Triploblastic Organization

• Diploblastic animals have cells arranged in two embryonic layers.
  • Ectoderm (outer layer) and endoderm (inner layer).
  • Example: Coelenterates
  • Mesoglea (undifferentiated layer) is found between ectoderm and endoderm.
• Triploblastic animals possess a third germinal layer (mesoderm) between the ectoderm and endoderm.
  • Seen in Platyhelminthes to chordates.

Coelom

• Coelom presence or absence is significant for classification.
• Coelom: body cavity lined by mesoderm.
• Coelomates: animals possessing a coelom.
  • Examples: annelids, mollusks, arthropods, echinoderms, hemichordates, chordates
• Pseudocoelomates: animals with scattered pouches between ectoderm and endoderm.
  • Example: Aschelminthes (nematodes)
• Acoelomates: animals lacking a body cavity.
  • Example: Platyhelminthes

Segmentation

• Segmentation: body divided into identical segments with serial repetition of organs.
• Metameric segmentation: seen in earthworms, where the body shows external and internal divisions (metamerism).

Notochord

• Notochord: rod-like structure derived from mesoderm during embryonic development.
• Chordates: animals with a notochord.
• Non-chordates: animals lacking a notochord.
  • Examples: Porifera to Echinodermata

Classification of Animals

• Classification based on fundamental features
• Chart shows an overview from previous sections describing these traits.

Phylum Porifera

• Members commonly known as Sponges
• Marine and mostly asymmetrical animals
• Primitive multicellular with cellular grade organization
• Water enters ostia, flows through spongocoel, exits via osculum

Phylum Coelenterata (Cnidaria)

• Aquatic, marine, sessile or free-swimming with radial symmetry.
• Cnidoblast: specialized cell used for anchorage, defense, and prey capture
• Exhibit tissue-level organization and diploblastic
• Gastrovascular cavity: central cavity with a single opening (hypostome) for digestion
• Digestion is extracellular and intracellular
• Some cnidarians produce a calcium carbonate skeleton, forming corals

Phylum Ctenophora

• Known as sea walnuts or comb jellies, exclusively marine with radial symmetry and diploblastic

Phylum Platyhelminthes

• Flatworms with dorsoventrally flattened body
• Endoparasites in animals, including humans
• Bilaterally symmetrical, triploblastic
• Acoelomate and organ-level organization
• Suckers and hooks present in parasitic forms
• Exchange of nutrients via absorption from host

Phylum Aschelminthes

• Roundworms with a circular body in cross-section
• Freeliving, aquatic, terrestrial, or parasitic on plants and animals
• Organ-system level organization

Phylum Annelida

• Aquatic (marine and fresh water) or terrestrial; free-living, sometimes parasitic; organ system-level organization.

Phylum Arthropoda

• Largest phylum with insects
• Exoskeleton made of chitin is a feature
• Tagmata: head, thorax and abdomen are often discrete body regions.

Phylum Mollusca

• Second largest animal phylum
• Terrestrial or aquatic, possess organ-system level
• Body covered by calcareous shell and unsegmented
• Distinct head, muscular foot, and visceral hump

Phylum Echinodermata

• Endoskeleton of calcareous ossicles gives name
• Exclusively marine with organ-system level
• Complete Digestive System
• Water vascular system aids locomotion, food capture
• Asexual reproduction

Phylum Hemichordata

• Small group of marine worm-like with organ-system level
• Bilaterally symmetrical, triploblastic
• Coelomate
• Body: proboscis, collar, trunk
• Open, respiratory via gills, excretory via proboscis gland
• Reproduction is sexual, external fertilization, indirect development

Phylum Chordata

• Presence of notochord, dorsal hollow nerve cord, paired pharyngeal gill slits
• Bilaterally symmetrical, triploblastic, coelomate, organ-system level

Summary of Key Traits

• Key features such as level of organization, symmetry, segmentation, and notochord enable animal kingdom's classification.
• These are specific unique traits for each phylum/class.