ZOOLOGY

• Integumentary Structures in Invertebrates

  • Protozoans
  • Sponges
  • Cnidarians
  • Flukes and Roundworms
  • Annelids
  • Arthropods
  • Mollusks
  • Echinoderms
• Protozoans


  • Exhibit diverse coatings, ranging from soft forms (e.g., Amoeba) to cuticles composed of proteinaceous or cellulose material
  • Some have shells incorporating foreign bodies like siliceous plates, calcium carbonate, or cellulose
• Sponges


  • Simple epithelium (pinacoderm) covering external surfaces and lining internal waterways
  • Deposition of needle-like spicules of calcium carbonate in the jelly beneath the outer epithelium
• Cnidarians


  • Epidermis provides basic integument features, including various cells like epithelial, contractile, gland, pigment, stinging, and sensory cells
  • Surface secretion aids in food capture, substrate adherence, debris cleaning, support, and protection
  • Some produce horny coverings or calcareous external skeletons
• Flukes and Roundworms


  • Parasitic flukes possess a thick integument with spines, sensory papillae, and secretory bodies for surface renewal
  • Roundworms have a thick, flexible cuticle with distinct zones
• Annelids


  • Thin, horny cuticle with pores for mucus secretion by epidermal glands
  • Some marine annelids have glands producing parchmentlike or calcareous tubes for dwelling
  • Earthworms and leeches have specialized epidermis in the clitellum region for cocoon secretion
• Arthropods


  • Elaborate exoskeleton with a tough chitinous cuticle and sclerotization for hardness
  • Cuticle acts as a waterproof covering; wax layer prevents desiccation, often protected by a cement-like substance secreted by dermal glands
  • Living structure capable of producing various structures and undergoing molting (ecdysis) for growth, hormonally controlled in insects
• Mollusks


  • Capable epidermis with ciliated epithelium, abundant gland cells for mucus secretion, and complex glands for specialized secretions (e.g., byssus threads, operculum)
  • Shell secreted by mantle epithelium with outer conchiolin layer, intermediate calcite layer, and inner nacreous layer used for pearl formation
• Echinoderms


  • Characterized by a calcareous exoskeleton, ranging from rigid armor (e.g., sea urchins) to leathery consistency (e.g., sea cucumbers)
  • Epidermis lies outside the skeleton; capable of nutrient absorption from seawater

  
• Skin Layers


  • Epidermis
  • Dermis
• Epidermis


  The outer layer consisting of closely packed cells that act as a barrier against chemicals, radiation, and microbes. It also gives rise to skin appendages.
• Dermis


  The thicker layer that provides physical protection, housing various structures like fibrous connective tissue, blood vessels, smooth muscle cells, and nerve endings.
• Skin Derivatives and Appendages

  • Skin Glands
  • Pigment Cells
  • Epidermal Scales
  • Claws, Nails, Hooves, Horns, and Antlers
  • Feathers and Hair
  • Fish Scales
  • Reptilian Scales
  • Bird Feathers
  • Mammalian Skin
• Skin Glands


  • Exocrine glands secrete products (e.g., mucin, sweat, oil, wax, milk, toxins, odoriferous substances) to the skin surface. These glands can be unicellular or multicellular, tubular or sac-like, and may secrete continuously or periodically.
• Pigment Cells


  • Fish possess chromatophores that change color by redistributing pigment within cells. Amphibians and reptiles have chromatophores, but birds and mammals have melanocytes for pigment production.
• Epidermal Scales


  • Found in reptiles, birds, and mammals, these are hardened extensions of the stratum corneum or bony scales. They cover various body parts, such as claws, beaks, tails, or the shells of turtles.
• Claws, Nails, Hooves, Horns, and Antlers

  • These are diverse appendages formed from keratin. Claws and nails are common in many animals, hooves in hoofed mammals, and horns in certain mammals. Antlers, specific to deer, are solid bone structures covered by skin.
• Feathers and Hair


  • Birds have feathers for flight and insulation. Feathers evolve from reptilian scales. Mammals have hair, which distinguishes them, along with other horny derivatives like nails, hooves, quills, and horns.
• Fish Scales


  • Fish possess various types of scales (cosmoid, placoid, ganoid, cycloid, ctenoid) with different structures, covering the skin for protection.
• Reptilian Scales


  • Reptiles have thickened, overlapping scales that prevent water loss. They vary in size, shape, and flexibility based on the species' lifestyle.
• Bird Feathers


  • Feathers in birds serve different purposes, such as flight, insulation, and display. They can vary in type, arrangement, and color, forming specific tracts and patterns.

  
• Mammalian Skin


  • Mammalian skin has several layers, including keratinocytes, melanocytes, Merkel cells, and Langerhans cells. The dermis comprises collagen, mucopolysaccharides, and contains various structures like glands, vessels, muscles, and nerves.
• Hair Functions


  • Insulation
  • Sensory Organs
  • Communication and Coloration
• Hair Structure


  • Each hair is a cylinder made of compacted and keratinized cells growing from a pit in the skin called the hair follicle. The follicle consists mainly of epidermal and dermal components.
  • The hair shaft is primarily composed of pigmented, horny, fibrous material known as the cortex, covered by a delicate layer of imbricated scales forming the cuticle.
  • Hair structure and cuticular scales vary among species, contributing to their unique appearance.
• Hair Growth Cycle


  • Hair follicles undergo cyclic activity involving periods of active growth (anagen), transition (catagen), and resting (telogen). The hair is shed (molted) after the cycle, and a new hair replaces it.
• Skin Glands


  • Mammals have three major types of skin glands: oil-secreting sebaceous glands, tubular glands associated with hair follicles, and merocrine glands not linked to hair follicles.
  • These glands serve various functions such as producing odors for communication, controlling temperature, and preventing slipping in some species.