INTEGUMENTRY SYSTEM IN MULTICELLULAR INVERTEBRATES || BSC ZOOLOGY C

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The integumentary system in multicellular invertebrates varies widely depending on the group but generally functions in protection, support, sensory reception, respiration, and secretion. Below is an overview of the integumentary system in major groups of multicellular invertebrates:

1. Porifera (Sponges)

Outer layer composed of pinacocytes (flattened cells).

No true epidermis, but a porous body with a gelatinous middle layer containing spicules or spongin fibers for structural support.


2. Cnidarians (Jellyfish, Corals, Sea Anemones)

Outer epidermis composed of epithelial cells, sensory cells, and cnidocytes (stinging cells).

Inner gastrodermis lines the digestive cavity.

Some have a protective exoskeleton (e.g., corals with calcium carbonate skeletons).


3. Platyhelminthes (Flatworms)

Free-living forms (e.g., planarians) have a ciliated epidermis with mucus-secreting cells for movement and protection.

Parasitic forms (e.g., tapeworms) have a tegument (thick, non-ciliated syncytial layer) that resists host digestive enzymes and aids in nutrient absorption.


4. Nematoda (Roundworms)

Covered by a thick, flexible cuticle made of collagen, secreted by the epidermis.

Provides protection from environmental stresses and host immune responses in parasitic species.


5. Annelida (Segmented Worms)

Covered by a thin, moist cuticle over a single-layered epidermis with mucus-secreting glands.

The moist surface facilitates gas exchange in terrestrial forms (e.g., earthworms).


6. Arthropoda (Insects, Crustaceans, Arachnids, etc.)

Possess a tough exoskeleton made of chitin and proteins, sometimes reinforced with calcium carbonate (e.g., in crustaceans).

The exoskeleton is periodically molted (ecdysis) for growth.

Specialized modifications include wax layers in insects to prevent water loss.


7. Mollusca (Snails, Clams, Squids, etc.)

The outer layer is a mantle, which secretes the shell in shelled mollusks (e.g., bivalves, gastropods).

The epidermis contains mucous glands, pigment cells, and sometimes sensory structures like photoreceptors.


8. Echinodermata (Starfish, Sea Urchins, etc.)

Covered by a thin epidermis over a calcareous endoskeleton made of ossicles.

Some have spines or pedicellariae for protection and cleaning.


Functions of Invertebrate Integuments

1. Protection – Against mechanical injury, predators, and environmental factors.


2. Support and Structure – Provides rigidity in some groups (e.g., arthropods).


3. Water Regulation – Prevents desiccation in terrestrial invertebrates.


4. Sensory Functions – Contains sensory cells for environmental interaction.


5. Respiration – Gas exchange occurs through the integument in some groups.


6. Secretion – Produces mucus, toxins, enzymes, or shells.

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