ANNELIDS WHAT IS AN ANNELID BELONG TO THE

ANNELIDS

WHAT IS AN ANNELID? • BELONG TO THE PHYLUM ANNELIDA. • INCLUDE EARTHWORMS, LEECHES, AND MARINE WORMS. • ANNELIDS HAVE SEGMENTS SEPARATED BY SEPTA – INTERNAL WALLS BETWEEN SEGMENTS. • THE SEGMENTS ARE VERY SIMILAR BUT THEY MAY BE MODIFIED FOR SPECIFIC REASONS LIKE A HEAD OR MOVEMENT. • THEY HAVE A TRUE COELOM (BODY CAVITY) THAT IS LINED COMPLETELY WITH MESODERM.

FORM AND FUNCTION IN ANNELIDS • ANNELIDS CAN RANGE FROM FILTER FEEDERS TO PREDATORS. THEY HAVE A PHARYNX THAT HAS 2 OR MORE SHARP JAWS. THEY ALSO HAVE A CROP WHERE FOOD CAN BE STORED. LASTLY THEY HAVE A GIZZARD THAT GRIND FOOD INTO SMALLER PIECES.

• ANNELIDS HAVE A CLOSED CIRCULATORY SYSTEM – THIS MEANS BLOOD IS MOVED THROUGH BLOOD VESSELS COMPLETELY.

• AQUATIC ANNELIDS HAVE GILLS. THIS IS AN ORGAN SPECIALIZED FOR GAS EXCHANGE UNDER WATER. • LAND DWELLING ANNELIDS, LIKE EARTHWORMS, DO GAS EXCHANGE THROUGH THEIR SKIN. THEY WILL HAVE A THIN COATING OF MUCUS TO KEEP THEIR SKIN MOIST.

• ANNELIDS HAVE A WELL-DEVELOPED NERVOUS SYSTEM WITH A BRAIN AND SEVERAL NERVE CORDS.

OLIGOCHAETES • THIS CLASS OF ANNELIDS HAS THE EARTHWORMS IN IT. • THEY HAVE FEW SETAE – LITTLE HAIRS THAT HELP THEM ANCHOR INTO THE DIRT AND MOVE. • MOST LIVE IN SOIL OR FRESH WATER. • EARTHWORMS EAT DIRT AND THEIR POOP IS CALLED CASTINGS. THIS IS VERY IMPORTANT FOR FERTILIZING THE SOIL AND FOR AERATING THE SOIL.

LEECHES • THIS IS CLASS HIRUDINEA. • LIVE IN MOIST HABITATS IN TROPICAL COUNTRIES. • LEECHES ARE EXTERNAL PARASITES THAT SUCK THE BLOOD AND BODY FLUIDS OF THEIR HOSTS. • LEECHES HAVE SUCKERS AT BOTH ENDS OF THEIR BODIES TO HELP THEM ATTACH TO THEIR HOST. • SOME LEECHES RELEASE A SUBSTANCE THAT KEEPS THE HOST FROM KNOWING THEY WERE BITTEN. • LEECHES CAN BE USED IN MEDICINE – THEY CAN REDUCE SWELLING AFTER SURGERY. THEY ALSO PREVENT BLOOD FROM CLOTTING SO IT CAN HELP WITH THE REATTACHMENT OF LIMBS.

POLYCHAETES • CLASS POLYCHAETA – SANDWORMS, BLOODWORMS, MARINE WORMS. • THEY HAVE PAIRED, PADDLE-LIKE APPENDAGES WITH SETAE ON THE END. THIS IS CALLED PARAPODIA.

ECOLOGY OF ANNELIDS • EARTHWORMS WILL BURROW THROUGH SOIL AERATING IT, AND MIXING IT. THIS ALLOWS ROOM FOR PLANT ROOTS TO GROW AND WATER TO MOVE SO THAT MANY PLANTS AND BACTERIA CAN THRIVE. • AS MENTIONED BEFORE CASTINGS ARE A GOOD FERTILIZER FOR SOIL. • MANY BIRDS EAT EARTHWORMS. THERE ARE OTHER ANIMALS, LIKE MOLES, SKUNKS, TOADS, AND SNAKES THAT EARTHWORMS.