ch. 24, section 3

sponge characteristics:

* no tissues, no organs, most lack symmetry


* can break down into individual cells which will reform a new sponge

what phylum do sponges belong to?

porifera (meaning pore bearer)

instead of having an endoderm and mesoderm, what are the two cell layers of a sponge?

1. epithelial-like cells: cover and protect the sponge
2. choanocytes: (collar cells) with flagella that line the inside of the sponge

flagella function:

whip back and forth to draw water into the body through pores

osculum function:

mouth-like opening at the top of the sponge where water and wastes will be expelled out

sponges are sessile filter feeders, meaning:

sessile: attached to stay in one place (as adults)

filter feeders: obtain food by filtering small particles out of the water

archaeocytes:

amoeba-like cells located between a sponge’s two cell layers that secrete spicules, make up the support structure, and are involved in digestion, egg/sperm production, and excretion

spicules:

small, needle-like structures that make up the support structures of sponges

what are the three classes sponges are split into based on their support system?

1. demospongiae
2. calcarea
3. hexactinellida

demospongjae:

have spicules composed of spongin fiber, silica, or both (won’t form net-like skeleton)

calcarea:

spicules are composed of calcium carbonate

hexactinellida:

spicules of silica joined together to make a net-like skeleton (glass sponges)

how do sponges respond to stimuli?

epithelial-like cells detect external stimuli and respond by closing their pores

what are gemmules?

formed by some freshwater sponges and are involved in asexual reproduction which develop during adverse conditions

benefits of sponges:

* are food for some fishes and turtles and forms habitats for a variety of animals
* used for household scrubbing purposes and in pharmaceutical products

cnidarians characteristics:

* phylum: cnidaria, contains jellyfish, sea anemones, and coral
* aquatic floating or sessile

cnidarian body structure characteristics:

* one body opening and two cell layers (which organize into tissues)
* outer layer provides protection, inner layer provides digestion
* most have radial symmetry
* no blood vessels, excretory organs, or respiratory system

cnidocytes:

stinging cell that arm the tentacles for feeding and digestion

cnidocytes contain nematocyst, which is:

a capsule that holds a coiled tube containing poison and barbs

how do cnidarians respond to stimuli?

they contain a nerve net that conducts impulses, the impulses cause contractions of muscle-like cells

what are the two body forms cnidarians have in reproduction?

a polyp and a medusa

polyps:

tube-shaped bodies with a mouth surrounded by tentacles

medusas:

umbrella-shaped bodies with tentacles hanging down

steps of reproduction in cnidarians:

1. (sexual stage) medusas release eggs and sperm into the water where fertilization occurs
2. zygotes develop into free-swimming larvae that settle and grow into poylps
3. (asexual stage) polyps reproduce asexually through budding which will form a new medusa (no free-swimming medusa which starts the cycle again)

what are the four main classes of cnidarians?

1. hydroids
2. jellyfish
3. sea anemones
4. corals

study where the mouth/anus and gastrovascular cavity of a polyp and a medusa is located at:

study where the osculum of a sponge is located at