1. Chapter 26-3
Cnidarians
by us three :)

2. Cnidarians are...
soft-bodied, carnivorous animals that have stinging tentacles arranged in circles around their mouths
the simplest animals to have body symmetry and specialized tissues
Cnidarians get their name from the cnidocytes, or stinging cells, that are located along their tentacles. Within each cnidocyte is a nematocyst, a poison-filled, stinging structure that contains a tightly coiled up dart.
Cnidarians include jellyfishes, hydras and their relatives, and sea anemones and corals.

4. Body Plan Cnidarians are radially symmetrical
central mouth surrounded by many tentacles that extend outward from body
typically have a life that includes two different-looking stages: a polyp and a medusa
both medusa and polyp have a body wall that surrounds a gastrovascular cavity, the gastroderm is the inner lining of the g.c, where digestion takes place, the epidermis is the outer layer of cells, the mesoglea is the layer that lies between these two tissues

5. Feeding & Respiration, Circulation, & Excretion
After paralyzing its prey, a cnidarian pulls the prey through its mouth and into its gastrovascular cavity
food enters and leaves through this opening
digestion takes place here and is extracellular, meaning it takes places outside of cells
Partially digested food is absorbed by the gastroderm
digestion is completed intracellularly, meaning within cells in the gastroderm
Any materials that can’t be digested are passed out of body through the mouth
After digestion, nutrients are usually transported throughout body by diffusion
cnidarians respire and eliminate wastes of cellular metabolism by diffusion through their bodies
THROW BACK!!
Diffusion is process by which molecules tend to move from an area where they are more concentrated to an area of low concentration
cannibalism

6. Response & Movement
Both polyp and medusa have a nerve net which is a loosely organized network of nerve cells that together allow cnidarians to detect stimuli such (ex.: the touch of a foreign object)
Nerve net is usually distributed uniformly around body, but in some species it is concentrated around the mouth or in rings around the body
Cnidarians also have:
statocysts, which are groups of sensory cells that help determine direction of gravity and ocelli, which are eyespots made of cells that detect light
different cnidarians move in different ways
sea anemones have a hydrostatic skeleton which is a layer of circular and longitudinal muscles that, with the water in the gastrovascular cavity, enable it to move
medusas, such as jellyfish, move by jet propulsion
this is when muscles contractions cause the bell-shaped body to close like an umbrella and push water out of the bell moves medusa forward

7. Reproduction Most cnidarians reproduce both sexually and asexually
Polyps can reproduce by budding
one type begins with a swelling on the side of an existing polyp that breaks off and becomes a new polyp
another is when polyps produce tiny medusas that separate and become new
individuals
In most cnidarians, sexual reproduction takes place with external fertilization, which the process in which the eggs are fertilized outside the female’s body

9. Hydras and their Relatives
Class Hydrozoa
polyps grow in branching colonies that sometimes extend more than 1 meter
within colony, polyps are specialized to perform different functions
(ex.: some digest food held by tentacles while others make eggs and sperm)
most common freshwater hydrozoans are hydras
lack medusa stage, instead live as solitary polyps
reproduce sexually and asexually
many get nutrient from small prey and some from symbiotic photosynthetic protists that live in their tissues

10. Sea Anemones and Corals
Class Anthozoa “flower animal”
only have polyp stage in their lives
many species are colonial
use nematocysts to capture prey for nutrition
new polyps produced by budding
as colony grows, they secrete underlying skeleton of calcium carbonate, or limestone
Worldwide distribution of corals determined by few factors:
Temperature 2) water depth 3) light intensity
light- corals rely on mutualistic relationships with algae that capture solar energy, recycle nutrients, & help corals lay down limestone
Harmed from human activities, logging, farming, mining, etc.
Coral bleaching caused by high temperatures can kill algae
that usually live in the tissues of corals, leaving behind only
transparent cells atop ghostly white skeletons
I live an anenemone… anemonmone..

11. Vocabulary cnidocytes, or stinging cells
nematocyst, a poison-filled, stinging structure that contains a tightly coiled up dart.
gastrovascular cavity digestive chamber with a single opening in which cnidarians, etc., digest food
gastroderm is the inner lining of the g.c, where digestion takes place
epidermis is the outer layer of cells
mesoglea is the layer that lies between the epidermis and gastroderm
extracellular, digestion takes places outside of cells
Intracellular digestion takes place inside of cells
nerve net which is a loosely organized network of nerve cells that together allow cnidarians to detect stimuli
statocysts, which are groups of sensory cells that help determine direction of gravity
ocelli, which are eyespots made of cells that detect light
hydrostatic skeleton which is a layer of circular and longitudinal muscles that, with the water in the gastrovascular cavity, enable it to move
jet propulsion this is when muscles contractions cause the bell-shaped body to close like an umbrella and push water out of the bell
external fertilization, which the process in which the eggs are fertilized outside the female’s body

12. Soft-bodied, carnivorous, and have stinging tentacles
Cnidarians are…
Soft-bodied, carnivorous, and have stinging tentacles
Simplest organism with body symmetry and specialized tissues
Named after their cnidocytes, or stinging cells, on their tentacles
Within cnidocytes, are nematocysts, poison-filled stinging structure with a dart
Include: jellyfishes, hydras, sea anemones, and corals
Body Plan
Radial symmetry
Two stages: Polyp and Medusa
Both have body wall surrounding a gastrovascular cavity which is lined with the gastroderm, where digestion takes place
Epidermis is the outer layer of cells
Mesoglea is the layer between the epidermis and gastroderm

13. Feeding, Respiration, Circulation, and Excretion Feeding:
paralyze the prey, pull it through the mouth, into the gastrovascular cavity, where extracelluar digestion, or outside of cells, occurs
food is then absorbed by gastroderm, where digestion is completed intracellularly, or within the cells
Food not digested, leaves through the mouth
Other body processes occur by diffusion
Response and Movement
Cnidarians have a nerve net, or a loosely organized network of nerve cells that allow the cnidarians to detect stimuli
They also have statocysts- groups of sensory cells that help determine direction of gravity
Also, they have ocelli- eyespots with cells that detect light
Movement:
Sea anemones- hydrostatic skeleton, which is a layer of muscles that, with water, enables it to move
Medusas- jet propulsion, works by forcing the bell shaped body to close like an umbrella, and push water out of the bell

14. Hydras and Their Relatives Class Hydrozoa
Reproduction
Asexually
Polyps reproduce by budding, either by a piece of the polyp swelling and breaking off into a new polyp, or by producing and releasing medusas
Sexual
Male release sperm, female release eggs, and external fertilization occurs, which is the process when the eggs are fertilized outside the female’s body
Hydras and Their Relatives
Class Hydrozoa
Polyps grow in branching colonies and each is specialized for a certain job
Hydras are the most common freshwater hydrozoans
lack medusa stage
reproduce sexually and asexually
get nutrients from small prey and some from symbiotic photosynthetic protists living in their tissues

15. Sea Anemones and Corals
Class Anthozoa- “flower animal”
Only polyp stage
Many are colonial
Use nematocysts to capture prey
New polyps produced by budding
As it’s growing, it secretes a skeleton of calcium carbonate, or limestone
Where corals grow is affected by temperature, water depth, and light intensity
Corals rely on mutualistic relationships with algae that capture solar energy, recycle nutrients, and help lay down limestone
Corals are harmed by human activities, logging, farming, mining, etc.
Coral bleaching caused by high temperatures kill algae in corals