Cnidarians PPT I.

Define what Phylum Cnidaria is

— Diploblastic animals with radial symmetry and cnidocytes, including jellyfish, corals, sea anemones, and hydroids.

What is a Cnidocyte

— Specialized stinging cell unique to cnidarians used for prey capture and defense.

What is Subkingdom Eumetazoa

— Animals with true tissues derived from germ layers.

What is the Most Primitive Eumetazoans

Cnidarians are among the earliest eumetazoans, appearing ~600 million years ago in the fossil record.

Radial Symmetry

— Body symmetry arranged around a central axis with no distinct head.

What is the Habitat of Cnidarians

— Mostly shallow marine environments, abundant in warm tropical waters, but also found in deep and Arctic oceans.

Di-/Polymorphic Body Forms

— Ability to exist in different body forms such as polyp and medusa.

Sessile

— Fixed in place and non-moving.

Sedentary

— Limited movement.

Polyp Form

— Vase-shaped body with mouth opening upward and limited movement

Medusa Form

— Umbrella-shaped body with mouth opening downward and free-swimming.

Respiratory System (Absent)

— Cnidarians lack specialized respiratory organs.

Excretory System (Absent) .

— Waste removal occurs by diffusion

Circulatory System (Absent)

— No blood vessels; materials circulate via the gastrovascular cavity.

Tissue-Grade Construction

— Organization at the tissue level rather than organ systems.

Diffusion

— Passive exchange of oxygen, nutrients, and wastes across body surfaces.

No True Organ Systems

— Cnidarians lack complex organs.

Diploblastic

— Having two embryonic germ layers.

Mesoglea

— Non-living jelly-like layer between epidermis and gastrodermis.

Diploblastic Body Wall

— Body wall composed of epidermis, mesoglea, and gastrodermis.

Gastrovascular Cavity (Coelenteron)

— Central cavity used for digestion, circulation, and hydrostatic support.

Hydrostatic Skeleton

— Fluid-filled cavity providing structural support and movement.

Nerve Net

— Mesh-like network of nerve cells beneath the epidermis without a central brain.

Sensory Receptors

— Cells that detect chemical signals or motion.

Taxis

— Movement toward or away from a stimulus.

Environmental Signal Pathway

— Sensory input → nerve net signal → contractile and pacemaker cells → movement response.

Extracellular Digestion

— Enzymes secreted into the gastrovascular cavity to break down food.

Intracellular Digestion

— Phagocytic cells digest food particles inside cells.

Interstitial Stem Cells

— Pluripotent cells capable of differentiating into multiple cell types.

Asexual Reproduction (Budding)

— New individuals form from buds produced by interstitial cells.

Sexual Reproduction

— Gametes produced from differentiated interstitial cells.

Differentiation

— Process by which interstitial stem cells become specialized cells.

Cnidocyte (Entire Cell)

— Whole stinging cell located primarily in the epidermis, especially on tentacles.

Nematocyst

— Stinging organelle inside the cnidocyte that delivers venom.

Cnidocyte vs Nematocyst

— Cnidocyte is the cell; nematocyst is the organelle inside it.

Cnidocil

— Hair-like trigger that detects physical or chemical stimuli.

Operculum

— Lid covering the nematocyst capsule.

Filament Tube

— Barbed, hollow thread that everts to inject venom.

Fastest Cellular Discharge

— Nematocyst firing occurs in ~700 nanoseconds.

Extreme Acceleration

— Discharge generates ~5,000,000×g acceleration.

High Osmotic Pressure

— Caused by high calcium ion concentration inside the cnidocyte.

Trigger Mechanism

— Contact or chemical cues make the membrane permeable.

Eversion —

Rapid uncoiling and outward firing of the nematocyst filament.

Neurotoxins

— Block ion channels and paralyze the nervous system.

Cytolysins

— Break down cell membranes, causing tissue necrosis.

Myotoxins

— Cause muscle contraction, paralysis, or heart failure.

Penetrant Nematocyst

— Type that pierces tissue and injects toxins.

Cnidarian Sting Pain

— Caused by injected toxins affecting nerves, muscles, and cells.

Primary function of cnidocytes to immobilize food.

Prey Capture

Feed on plankton, invertebrates, fish eggs, larvae, and even whole fish that get close to them

Opportunistic Carnivores —

how do cnidarians get Defense Against Predators

— Cnidocytes deter larger animals from predation.

What is Substrate Attachment

Cnidocytes anchor sessile cnidarians to surfaces.

how do cnidarians do Construction

— Cnidocytes help build protective structures such as tube anemones.

how do cnidarians produce Locomotion

— Sticky filaments allow looping or somersaulting movement.