phylum+annelida

ZOOLOGY NOTES—PHYLUM ANNELIDA, THE SEGMENTED WORMS GENERAL FACTS ABOUT ANNELIDS ü THE WORD ANNELIDA MEANS ‘LITTLE RING’ ü 15,000 SPECIES; EARTHWORMS AND LEECHES ARE THE MOST WELL-KNOWN SPECIAL CHARACTERISTICS OF ANNELIDS · BODY SEGMENTATION, OR METAMERISM, FIRST APPEARS IN THIS GROUP. THIS ALLOWS FOR REPETITION OF COMPONENTS OF SOME BODY SYSTEMS. THIS SERVES AS A SAFETY FACTOR; IF ONE SEGMENT FAILS, THE RESULTS ARE NOT NECESSARILY FATAL. THE SEPTA, WHICH DIVIDE THE SEGMENTS, ALSO ALLOW FOR MORE CONTROL OF BODY MOVEMENTS. · PAIRED STRUCTURES CALLED PARAPODIA SUGGEST THE INTRODUCTION OF PAIRED APPENDAGES IN THIS GROUP · SOMETIMES CALLED ‘ BRISTLE WORMS’, MOST ANNELIDS HAVE TINY BRISTLES (SETAE) MADE OF CHITIN WHICH ALLOW THEM TO ANCHOR THEMSELVES DURING LOCOMOTION · CLOSED CIRCULATORY SYSTEM WITH AORTIC ARCHES, OFTEN CALLED ‘HEARTS’ · WELL-DEVELOPED COELOM · RESPIRATORY GASES EXCHANGED THROUGH THE SKIN, GILLS, OR PARAPODIA · BILATERAL SYMMETRY · EXCRETORY SYSTEM HAS A PAIR OF NEPHRIDIA (KIDNEY-LIKE STRUCTURES) IN EACH METAMERE · DIGESTIVE SYSTEM COMPLETE · WELL-DEVELOPED NERVOUS SYSTEM · MONOECIOUS OR DIOECIOUS ANNELID CLASSIFICATION v CLASS POLYCHAETA—LARGEST GROUP WITH OVER 10,000 SPECIES—CLAM WORMS, //Nereis// v CLASS OLIGOCHAETA—EARTHWORMS, //Lumbricus terrestris// v CLASS HIRUDINEA—LEECHES, //Hirudo//