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Phylum Platyhelminthes: Definition, Characteristics, Classification and Examples

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Definition, Characteristics, Classification and Examples of Phylum Platyhelminthes

Phylum Platyhelminthes (Gr., platys = flat ; helmins = worms) refers to a group of invertebrate animals commonly known as flatworms. They are characterized by their soft, unsegmented, dorsoventrally flattened bodies. Members of this phylum are bilaterally symmetrical, triploblastic (having three embryonic germ layers), and acoelomate, meaning they lack a true body cavity. Platyhelminthes exhibit cephalization (a distinct head region) and possess a simple organ system level of organization.

Phylum Ctenophora: Definition, Characteristics, Classification and Examples

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Definition, Characteristics, Classification and Examples of Phylum Ctenophora

Phylum Ctenophora (Gr., kestos=comb; phoros=bearing) is a group of marine invertebrates commonly known as comb jellies. These organisms are characterized by their gelatinous bodies, biradial symmetry, and the presence of eight rows of ciliary plates (combs) that they use for locomotion. Unlike jellyfish, which belong to Phylum Cnidaria, ctenophores lack stinging cells (cnidocytes) and instead capture prey using sticky cells called colloblasts.

Viruses: Definition, Characteristics, Morphology and Classification

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Structure of Virus labelled Diagram

Viruses are intracellular obligate parasites, non-cellular (acellular) sub-microscopic organisms. The word “virus” means venom or poisonous fluid. They lack cell organelles and make use of the protein synthetic machinery of the host cell.

Coral Reefs: Definition, Types, Formation and Economic Importance

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Types of Coral Reefs

Coral colonies grow continuously in size by budding of polyps and often form extensive masses, known as coral reefs.

Polymorphism in Coelenterates

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Polymorphism in Coelenterates

Occurrence of more than one type of individuals in the same species, which differ in form and function, is known as polymorphism.

Aurelia aurita: Classification, Morphology and Life cycle

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External morphology diagram of Aurelia aurita

Aurelia aurita is easily recognised by its soft bell or umbrella-shaped body with four red or purple horseshoe-shaped gonads on its upper surface and four long and narrow oral lobes hanging downward from the lower surface.

Phylum Coelenterata: Definition, Characteristics, Classification and Examples

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Definition, Characteristics, Classification and Examples of Phylum Coelenterata

Phylum Coelenterata (Gr., koilos = hollow ; enteron = intestine), also known as Phylum Cnidaria, is a group of aquatic, mostly marine animals characterized by a simple body structure with a single opening serving as both mouth and anus. Members of this phylum have a diploblastic body (two tissue layers: ectoderm and endoderm) and radial symmetry. They possess specialized stinging cells called cnidocytes containing nematocysts, used for defense and capturing prey. Coelenterates exhibit two main body forms: the sessile polyp (e.g., Hydra) and the free-floating medusa (e.g., jellyfish). This phylum includes organisms like corals, sea anemones, and hydroids, playing important roles in marine ecosystems, such as reef-building.

Differences between Apoptosis and Necrosis

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Differences between Apoptosis and Necrosis

The main difference between apoptosis and necrosis is the way in which cell death occurs. Apoptosis is a programmed and controlled process of cell death that plays a vital role in normal development, tissue maintenance, and removing damaged cells. It does not cause inflammation as the cell contents are contained and recycled. Necrosis, on the other hand, is an uncontrolled and unplanned cell death caused by injury, infection, or toxins, often leading to inflammation as the cell contents are released into the surrounding tissue.

Canal System in Sponges

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Sycon type of Canal System in Sponges

Inside the body of Sponges, the water current flows through a certain system of spaces collectively forming the canal system in sponges.

Differences between Innate and Adaptive Immunity

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Difference between Innate and Adaptive Immunity

The main differences between Innate and Adaptive Immunity lies in their response mechanisms and specificity. Innate immunity is the body’s first line of defense and provides a rapid, non-specific response to infections. It includes physical barriers (like skin), chemical barriers, and immune cells like macrophages. In contrast, adaptive immunity is specific to particular pathogens and develops over time, involving specialized cells like T and B lymphocytes that create memory for future immune responses.