Annelids are segmented worms that include earthworms, leeches, and bristle worms. They are divided into three classes based on characteristics like the presence of bristles. Polychaetes are bristle worms that live mainly in marine environments. Oligochaetes include earthworms and live in soil and freshwater. Leeches can be found in freshwater or terrestrial environments. Annelids have bilateral symmetry and segmented bodies, and most reproduce sexually. They play important ecological roles in areas like soil enrichment.

2. WHAT ARE ANNELIDS?
• THE ANNELIDS, ALSO KNOWN AS THE RINGED WORMS OR
SEGMENTED WORMS, ARE A LARGE PHYLUM, WITH OVER
17,000 EXTANT SPECIES INCLUDING RAG WORMS,
EARTHWORMS, AND LEECHES.

3. CLASSES OF ANNELIDS
ANNELIDA IS DIVIDED INTO THREE
CLASSES:
 POLYCHAETE-/ (BRISTLE WORMS)
THESE ARE MARINE WORMS.
THEY VARY IN SIZE FROM A FEW
MILLIMETERS TO ABOUT 3 M (10 FEET)
AND ARE DIVIDED INFORMALLY INTO
TWO GROUPS; THE ERRANTIA, OR FREE-
MOVING FORMS, AND SEDENTARIA, OR
TUBE-DWELLING FORMS. THE BODY IS
OFTEN BRIGHTLY COLORED.

4. • POLYCHAETES ARE TYPICALLY MARINE
ANNELIDS THAT HAVE MANY BRISTLES
PROTRUDING FROM THEIR BODIES. BECAUSE
OF THIS, THEY ARE ALSO COMMONLY
KNOWN AS BRISTLE WORMS
• POLYCHAETES REPRODUCE SEXUALLY AND
CAN BE FOUND BURROWING ON THE SHORE,
FLOATING NEAR THE SURFACE OF THE
WATER, OR LIVING IN THE DEPTHS OF THE
OCEAN. UNLIKE THE OTHER CLASSES OF
ANNELIDS, WHICH ALL HAVE THE SAME
GENERAL APPEARANCE, POLYCHAETES
HAVE A WIDE VARIETY OF BODY FORMS.

5. OLIGOCHAETA/(EARTHWORMS)
 OLIGOCHAETA DO NOT HAVE MANY BRISTLES PROTRUDING FROM THEIR
BODY LIKE THE POLYCHAETES. IN FACT, ANY PROTRUSIONS THAT MAY EXIST
UNNOTICEABLE WITHOUT A CAREFUL EXAMINATION.
OLIGOCHAETES ARE TYPICALLY FOUND LIVING IN SOIL OR FRESH WATER AND
MOST FEED ON DECAYING MATTER.
EVERY OLIGOCHAETE IS HERMAPHRODITIC

6. HIRUDINEA/(LEECHES)
MOST LEECHES ARE FRESH WATER. SOME ARE MARINE. SOME ARE
COMPLETELY TERRESTRIAL. LEECHES PREY ON SMALL INVERTEBRATES
OR THEY FEED ON THE BODY FLUIDS OF VERTEBRATES.
ALL LEECHES ARE HERMAPHRODITIC THEY CANNOT SELF-FERTILIZE,
HOWEVER, BUT MUST MATE BECAUSE THEIR EGGS AND THEIR SPERM
DEVELOP AT DIFFERENT TIMES

7. • THEIR BODIES ARE MUCH MORE SOLID AS THE SPACES IN
THEIR COELOM ARE DENSE WITH CONNECTIVE TISSUES. THEY ALSO
HAVE TWO SUCKERS, ONE AT EACH END.
• THEY DIFFER FROM THE OLIGOCHAETES IN SIGNIFICANT WAYS. FOR
EXAMPLE, LEECHES DO NOT HAVE BRISTLES AND THE EXTERNAL
SEGMENTATION OF THEIR BODIES DOES NOT CORRESPOND WITH
THE INTERNAL SEGMENTATION OF THEIR ORGANS.

8. BODY SYMMETRY AND BODY PLAN
Annelids are all bilaterally symmetrical animals.
They range in size from much less than 1 mm in length to more
than 3 m.
 SEGMENTATION
Annelids were the first segmented animals.
Each segment contains digestive, excretory, circulatory,
and locomotor (movement) organs.

9. • NEARLY ALL ANNELIDS HAVE A FLUID-FILLED CAVITY
BETWEEN THE OUTER BODY WALL AND THE GUT, AND THIS IS
REFERRED TO AS A COELOM
• THE COELOM IS GENERALLY ORGANIZED AS A SERIES OF
COMPARTMENTS DIVIDED BY INTERSEGMENTAL SEPTA. THIS
COMPARTMENTALIZATION MEANS THAT IF THE WORM IS
DAMAGED THE COELOMIC CONTENTS WILL ONLY BE LOST
FROM A FEW SEGMENTS, AND LOCOMOTION CAN BE
MAINTAINED.

10. • SEPTUMS HELP SEPARATE AN EARTHWORM'S INTERNAL CAVITIES
INTO SECTIONS OF DIFFERENT ORGANS. THROUGH THE LENGTH OF
AN EARTHWORM, SOME ORGANS ARE REPEATED. INSIDE AN
EARTHWORM IS AN ENTIRE DIGESTIVE SYSTEM THAT IS CARRIED
THROUGHOUT THE SEGMENTS.
• MOST SEGMENTS CONTAIN NEPHRIDIA, ORGANS THAT FUNCTION
LIKE KIDNEYS. SEVERAL SEGMENTS CONTAIN HEARTS, WHILE
SEVERAL OTHERS CONTAIN TESTES. THIS IS WHY CUTTING AN
EARTHWORM IN CERTAIN SPOTS WILL RESULT IN SEVERAL WORMS
THAT ARE CAPABLE OF INDEPENDENT FUNCTIONING.

11. • THE SETAE ("HAIRS") OF ANNELIDS PROJECT OUT FROM
THE EPIDERMIS TO PROVIDE TRACTION AND OTHER
CAPABILITIES. THE SIMPLEST ARE UNJOINTED AND FORM
PAIRED BUNDLES NEAR THE TOP AND BOTTOM OF EACH
SIDE OF EACH SEGMENT. THE PARAPODIA ("LIMBS") OF
ANNELIDS THAT HAVE THEM OFTEN BEAR MORE
COMPLEX CHETAE AT THEIR TIPS – FOR EXAMPLE
JOINTED, COMB-LIKE OR HOOKED

13. FEEDING, DIGESTION AND EXCRETION IN ANNELIDS
• BURROWING ANNELIDS, LIKE THE EARTHWORM, PLAY AN
IMPORTANT ROLE IN HELPING ORGANIC MATTER
DECOMPOSE. EARTHWORMS EAT DEAD PLANTS AND
ANIMALS. WHEN THEY EAT, THEY ALSO TAKE IN SOIL
AND TINY PEBBLES. EARTHWORMS TAKE IN NUTRIENTS
FROM MICROORGANISMS IN THE MATERIAL THEY INGEST.

14. • THEY GET FOOD BY SCAVENGING (EARTHWORMS AND
LEECHES),
• BEING PREDATORS (LEECHES AND BRISTLE WORMS),
• OR PARASITES (LEECHES)
• BRISTLE WORMS:
• SELECTIVE DEPOSIT FEEDERS GENERALLY LIVE IN TUBES ON THE SEA-FLOOR AND
USE PALPS TO FIND FOOD PARTICLES IN THE SEDIMENT AND THEN WIPE THEM INTO
THEIR MOUTHS. FILTER FEEDERS USE "CROWNS" OF PALPS COVERED IN CILIA THAT
WASH FOOD PARTICLES TOWARDS THEIR MOUTHS. NON-SELECTIVE DEPOSIT
FEEDERS INGEST SOIL OR MARINE SEDIMENTS VIA MOUTHS THAT ARE GENERALLY
UNSPECIALIZED

16. REPRODUCTION IN ANNELIDS
• REPRODUCTION IS SEXUAL OR ASEXUAL.
• ASEXUAL REPRODUCTION IS BY FRAGMENTATION,
BUDDING, OR FISSION.
• AMONG SEXUALLY REPRODUCING
ANNELIDS HERMAPHRODITES ARE COMMON, BUT MOST
SPECIES HAVE SEPARATE SEXES. FERTILIZED EGGS OF
MARINE ANNELIDS USUALLY DEVELOP INTO FREE-
SWIMMING LARVAE.

17. EARTHWORMS
• THE MATING PAIR OVERLAP FRONT ENDS VENTRALLY AND EACH
EXCHANGES SPERM WITH THE OTHER.
• THE CLITELLUM BECOMES VERY REDDISH TO PINKISH IN COLOR.
SOME TIME AFTER COPULATION, LONG AFTER THE WORMS HAVE
SEPARATED, THE CLITELLUM (BEHIND THE SPERMATHECAE)
SECRETES MATERIAL WHICH FORMS A RING AROUND THE WORM.
• THE WORM THEN BACKS OUT OF THE RING, AND AS IT DOES SO, IT
INJECTS ITS OWN EGGS AND THE OTHER WORM'S SPERM INTO IT.

18. • AS THE WORM SLIPS OUT OF THE RING, THE ENDS OF THE COCOON
SEAL TO FORM A VAGUELY LEMON-SHAPED COCOON IN WHICH THE
EMBRYONIC WORMS DEVELOP.
• THEY EMERGE AS SMALL, BUT FULLY FORMED EARTHWORMS, BUT
LACK THEIR SEX STRUCTURES, WHICH DEVELOP IN ABOUT 60 TO 90
DAYS. THEY ATTAIN FULL SIZE IN ABOUT ONE YEAR.

19. BRISTLE WORMS
• THEIR GAMETES ARE PRODUCED IN THE COELOMIC LINING,
WHERE THEY ARE RELEASED INTO THE COELOM TO MATURE.
THESE GAMETES ARE THEN PICKED UP BY THE METANEPHRIDIA
SYSTEM AND RELEASED INTO THE AQUATIC ENVIRONMENT,
WHERE FERTILIZATION TAKES PLACE.
• ALTHOUGH SOME SPECIES HATCH DIRECTLY INTO THE ADULT
FORM, MANY HAVE A TROCHOPHORE LARVA, WHICH
METAMORPHOSES INTO THE ADULT AFTER ANYTHING FROM A
DAY TO A MONTH, DEPENDING ON SPECIES.

20. LEECHES
• LEECHES ARE HERMAPHRODITES
• REPRODUCTION OCCURS THROUGH THE PRODUCTION OF COCOONS THAT
ARE ATTACHED TO A SUBSTRATE WHERE THEY DEVELOP.
• LEECHES HAVE INTERNAL FERTILIZATION WITH MOST MATING BY
IMPLANTING A "SPERMATOPHORE" (SPERM PACKAGE) INTO THEIR
PARTNER. THIS IMPLANTATION CAN BY DONE THROUGH THE USE OF A
PROTRUSIBLE PENIS OR BY THE HYPODERMIC IMPLANTATION OF THE
SPERMATOPHORE INTO THE BODY OF THE PARTNER. THE SPERM ARE
THEN TRANSPORTED TO THE EGGS WHERE FERTILIZATION OCCURS.

21. RESPIRATION
•IN SOME ANNELIDS, INCLUDING EARTHWORMS,
ALL RESPIRATION IS VIA THE SKIN. HOWEVER,
MANY POLYCHAETES AND SOME CLITELLATES (THE GROUP
TO WHICH EARTHWORMS BELONG) HAVE GILLS
ASSOCIATED WITH MOST SEGMENTS, OFTEN AS
EXTENSIONS OF THE PARAPODIA IN POLYCHAETES. THE
GILLS OF TUBE-DWELLERS AND BURROWERS USUALLY
CLUSTER AROUND WHICHEVER END HAS THE STRONGER

22. LOCOMOTION/ MOVEMENT
• FIND A VIDEO OF WORMS MOVING

23. SENSITIVITY
• THE BRAIN GENERALLY FORMS A RING ROUND
THE PHARYNX (THROAT), CONSISTING OF A PAIR
OF GANGLIA (LOCAL CONTROL CENTERS) ABOVE AND IN FRONT OF
THE PHARYNX, LINKED BY NERVE CORDS EITHER SIDE OF THE
PHARYNX TO ANOTHER PAIR OF GANGLIA JUST BELOW AND BEHIND
IT.[7] THE BRAINS OF POLYCHAETES ARE GENERALLY IN THE
PROSTOMIUM, WHILE THOSE OF CLITELLATES ARE IN THE
PERISTOMIUM OR SOMETIMES THE FIRST SEGMENT BEHIND THE

25. REFERENCES
• HTTPS://EN.WIKIPEDIA.ORG/WIKI/ANNELID
• HTTP://ANNELIDA.WEEBLY.COM/SYMMETRY--BODY-PLAN.HTML
• HTTP://TOLWEB.ORG/ACCESSORY/CHARACTERISTICS_OF_ANNELIDA?ACC_ID=57
• HTTPS://SCIENCING.COM/FUNCTIONS-SEPTUM-EARTHWORM-12017983.HTML
• HTTPS://REPRODUCTIONSYSTEMPROJECT.WEEBLY.COM/ANNELIDA.HTML
• HTTPS://WWW.YOUTUBE.COM/WATCH?V=4ENZ3SI6UHC