Biology- Mr. Willets
Annelids / Mollusks
Members of Phylum Annelida are commonly called the segmented worms. Their bodies are divided into sections which can be easily seen on the outside of the earthworm. The name annelid means "little rings" which describes what the skin of an earthworm looks like.
Annelids are coelomates. The places inside the body where the organs are attached are seen as the lines on the outside of the body. Annelids are the first animal group to have blood. They have closed circulation although most are somewhat slow moving. They have a large dorsal blood vessel which can be seen through the skin. Certain blood vessels are enlarged and serve as "hearts" to pump the blood.
The brain is dorsal and the main nerve is ventral. This arrangement is known as the annelid type nervous system. This requires nerves to go around the gut to connect the brain to the main nerve.
Most annelids respire through moist skin. On land, this means the earthworm must remain underground during the day (unless it rains). At night, they come out to feed (they eat dirt and digest whatever organic matter is in it). This is why they are sometimes called night-crawlers. Some marine annelids (polychaetes) have simple gill-like structures.
The gut of annelids has specialized organs - each having its own function. You will see this in lab.
There are three basic kinds of annelids. Earthworms, leeches and polychaetes (seaworms). Earthworms loosen the soil as they move and enrich the soil with their feces. They are a sign of good soil. Leeches are fresh-water external parasites and feed on blood. Their saliva contains an anesthetic (so we don't feel the pain) and an anti-coagulant (keeps the blood from clotting so they can keep feeding). There are times when doctors do not want your blood to clot and they use leeches for that purpose.
Polychaetes are varied. Some common ones around here are called sea worms, clam worms, shimmy worms. They are sold as bait at the beach. Some of these have jaws, sense organs and leg-like structures. These are fast moving and hunt for smaller worms. Other polychaetes are filter feeders or eat sand and digest the organic matter in it. They are slow, have neither jaws nor sense organs.
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Phylum Mollusca (the mollusks) contains a wide variety of animals. What they have in common is:
a) siphons (tubes) that bring water into the mantle cavity (these
tubes are the "neck" of a steamer)
b) a muscular foot used for movement (the "chewy" part of a clam)
c) a visceral mass- a large area where the internal organs are
located (the belly of the clam)
d) a mantle- a thin layer of cells that secrete the shell (if they
have one)
e) a mantle cavity- a place where the gills are located. Water enters
and leaves here.
The three main kinds of mollusks are -
Bivalves- clams, oysters, mussels- these have a two part shell which is what the word bivalve means
Gastropods- snails, slugs (gastropod means "stomach foot")
Cephalopods- octopus, squid, nautilus (cephalopod means "head foot")
The incurrent and excurrent siphons are used mostly to bring water over the gills but also can bring food in for bivalves that are filter feeders. The fast moving mollusks (cephalopods) use the excurrent siphon for jet propulsion. They shoot water out a high speed which pushes them in the other direction.
The muscular foot is used by many bivalves to dig into the sand. Those that do this extend their siphons up into the water. If you are digging for clams, this is what you look for. Gastropods ripple their foot to move slowly (sedentary) and cephalopods have many muscular tentacles instead of one foot. These tentacles can be used to grab their food or to crawl along the bottom.
Bivalves and gastropods have open circulation. Cephalopods have closed circulation. Bivalves have few if any sense organs. Gastropods and cephalopods have sense organs. The eyes of an octopus are very good.
Bivalves mostly filter feed. Gastropods are grazers. They have a scraper (radula) in the mouth that can rip algae off of rocks. Cephalopods hunt and have a strong jaw like structure for crunching the shells of lobsters.
Bivalves are generally sessile and rely on their shell for protection. Scallops are bivalves that open and close their shells rapidly to force water out. This allows them to move. The part of the scallop we eat is the muscle that does this. Gastropods come partially out of their shell to feed. Cephalopods do not have a shell. They rely on speed to escape danger and in some cases can change color to camouflage themselves. Some spray ink into the water to cover their escape. One cephalopod, the nautilus has a shell but it has air-filled chambers so it floats and does not slow the animal down.
Questions
1) What external (outside of body) evidence is there that earthworms are coelomates? _______________
____________________________________________________________________________
2) What are the two main parts of the annelid type nervous system? ____________________________
____________________________________________________________________________
3) Annelids are the first phylum to have ____________ What type of circulation do they have? _________
This is usually associated with animals that __________________ although most annelids don't.
4) Earthworms usually remain underground during the day to prevent _____________________ If this happened, they would not be able to ________________________ since they use their skin to do this and it must be kept __________
5) What do leeches have in their saliva that helps them to feed? _________________________ and ___________________________
6) In what ways are earthworms good for the soil? _____________________________________ and _________________________________________________
7) Where do polychaetes live? ____________________________ The polychaetes that are hunters would have what characteristics? ________________________________________________
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8) The three main kinds of annelids are ____________________, ____________________ and ____________________________
9) The three main kinds of mollusks are-
a) ___________________________- give an example_________________
b) ___________________________- give an example_________________
c) ___________________________- give an example _________________
10) In gastropods, the ______________ is located near the foot. In cephalopods, the ____________ is located near the foot. (Hint- what do the words mean?)
11) Bivalves have two ____________________ Which bivalve can open and close its shells to allow it to move? __________________
12) The tubes that bring water in and out of the mollusk are called the ___________________________ and the ______________________________ These are used mostly to bring water over the _________________ to get oxygen. Bivalves also use these tubes to bring in _________________ (bivalves are ________________feeders) Cephalopods (like the squid and octopus) can shoot water out of these tubes to move. This is an example of ____________________Third Law of Motion which says that for every ______________________ there is an ______________________________________
When different mollusks use these tubes for different purposes, this is an example of _________________ evolution.
13) Cephalopods have __________ circulation. This is so they can ________fast in order to ________ their food. They have good __________ to locate their prey and muscular ____________________ to grab their food. They have a strong _________________ to actually eat their prey. They have no shell for protection but this allows them to be ________ Which cephalopod does have a shell? ________________
Why does this shell not slow down the animal? ____________________________________________
14) Bivalves get a great deal of _____________________ from their shell but this means they can't _________________ and must get their food by ______________________. They have _________ circulation and few if any ______________ organs. Which bivalve do you think would have eyes to see danger coming and therefore escape? __________________________