Sponges and Cnidarians

Ch. 26 Section 2 and 3


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


-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.


-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


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


- A cnidarian only has one opening in its body which is where food enters and waste leaves

-Digestion begins in the gastrovascular cavity, extracellularlly or outside of the cells

-Digestion ends inter cellularly or within the cells


-Different Cnidarians move in different ways

-Some use their hydrostatic skeleton, this happens when their circular muscles contract, making their bod become taller

-Others move by jet propulsion


-Most cnidarians can reproduce sexually or asexually

-Polyps can reproduce asexually by budding

-Cnidarians reproduce sexually with external fertilization, the egg and sperm are released into the water

Groups of Cnidarians

Ecology of Corals

-Coral Reefs are suffering from human activity, this includes diving, silt from logging and farming, insecticides and overfishing

-Coral bleaching has also become a problem, this is when high temperatures kill algae that would normally live on coral