Sponges and Cnidarians
Ch. 26 Section 2 and 3
Sponges
What is a Sponge?
-Sponges have tiny openings, or pores, all over their bodies
- Sponges are sessile, they live in one spot for their whole adult life
- They are considered animals because they are multicellular, heterotrophic, have no cell wall, and have specialized cells
Form and Function in Sponges
Body Plan
- Sponges have no tissues or organ systems
-In Sponges, simple physiological processes are carried out by specialized cells
- Sponges are asymmetrical and have no front, back, or sides
-Sponges have Choanocytes cells that use flagella to move water through the sponge, this water leaves through the osculum
-The movement of water provides a simple mechanism for feeding, respiration, circulation, and excretion
-Sponges have a simple skeleton. Soft sponges have a skeleton made of Spongin, hard sponges have a skeleton made of spiny spicules, or spike-shaped structure
Feeding
-Sponges sift microscopic food particles through the water
-Digestion takes place inside the cells
-As the food particles move through the cell, they are engulfed by choanocytes, then are passed on to the archaeocytes that complete the digestion process.
Reproduction
-Sponges can reproduce either sexually or asexually
-Most sponges can produce both eggs and sperm by meiosis, but at different times
-Eggs are fertilized inside the sponges body through internal fertilization
-Sperm can be carried from one sponge to another by water currents
-After fertilization, the zygote develops into larva and then are carried to the ocean floor
-In sexual reproduction the sponge is not identical to either parent
-Sponges can reproduce asexually by budding, which is when a part of the sponge breaks off to form a new sponge
-In asexual reproduction the sponge is identical to the parent
Ecology of Sponges
-Sponges are very important in aquatic ecology, they can provide homes for animals such as snails, sea stars, and shrimp
-Photosynthetic organisms such as bacteria and algae can provide food and oxygen in exchange for an area to live and thrive
-Sponges usually live attached to the sea floor, where they receive low levels of sunlight
-To get the sun they need for photosynthesis, some sponges have a antennae that can focus and direct incoming sunlight
Cnidarians
What is a Cnidarian?
-The phylum Cnidaria contains hydras, jellyfish, sea anemones, and corals
-They are soft-bodied, carnivorous, with stinging tentacles around their mouths
-They have stinging cells or cnidocytes that are used for self defense and capturing prey
-In each cnidocytes there is a nematocyst which is filled with poison, which is used to kill or paralyze prey
Form and Function in Cnidarians
Body Plan
-Cnidarians are only a few cells thick and have simple body systems
-Cnidarians are radically symmetrical, and usually have a life cycle that includes two different stages, polyp and Medusa
-Cnidarians have a internal space called a gastrovascular cavity, which is where digestion takes place
-Nutrients are transported through the body by diffusion
Feeding
-Digestion begins in the gastrovascular cavity, extracellularlly or outside of the cells
-Digestion ends inter cellularly or within the cells
Movement
-Some use their hydrostatic skeleton, this happens when their circular muscles contract, making their bod become taller
-Others move by jet propulsion
Reproduction
-Polyps can reproduce asexually by budding
-Cnidarians reproduce sexually with external fertilization, the egg and sperm are released into the water
Groups of Cnidarians
Jellyfish
Hydras
Sea Anemones and Coral
Ecology of Corals
-Coral bleaching has also become a problem, this is when high temperatures kill algae that would normally live on coral