PHYLUM ANNELIDA
RING WORMS
Oligochaeta
P o l y c h a e t a
Hirudinea
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Phylum Annelida-Ring worms
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marine, fresh water & moist land habitats
Protostomian coelomates
Vermiform, worm like
Soft bodied
Round in cross section
Metameric segmentation with septa between segments: replication of organs
Locomotion is a function of circular and longitudinal muscle contraction in individual
segments or group of segments and prevent deformation
Oblique muscles: maintain body turgor and operate parapodia
move by peristalsis-a type of locomotion produced by rhythmic waves of
muscle contractions passing from head to tail
hydrostatic skeleton by coelomic fluid in individual segments
flexible thin outer body wall: permeable for gas
Gas exchange through moist epidermis that forms the body wall with or without
cuticle secreted by epidermis.
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Metanephridia
waste removal
• Little kidney
• Each segment contains
2 nephridia
• Each opens at both
ends with 2 opinings
• ciliated funnels called
nephrostomes that
remove wastes from
the blood and
coelomic fluids
Parapodia
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Parapodia present in some groups
One or many pairs of chitinous bristles
called setae (chaetae).
Functions:
– Morphology needs for classification
– Highly vasculized- exchange of gases
– Locomotory function
– Some species with overlapping elytra
protective plates
Phylum Annelida-Digestive system
• Complete compartmentalized
digestive system in most
groups: mouth, pharynx,
esophagus, intestine, rectum,
anus.
Pharynx is associated with
salivary glands (that secrete
hirudin anticoagulant in
Hirudinea),
Esophagus may lead to a crop
then gizzard and associated
with calciferous glands- for
control of Ca ion concentrationin oligochaeta,
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Phylum Annelida- Circulatory system
• Closed
• Consists of dorsal blood vessel (carrying blood
towards anterior end)
• ventral blood vessel (carrying blood towards
posterior end)
• capillaries that connect the two vessels
• Contraction of blood vessels and valves ensure
circulation and movement of blood in one
direction
• Anterior blood vessels (5 pairs) connecting
between dorsal and ventral blood vessels may be
enlarged to act as hearts
• Blood pigment mostly hemoglobin but some
polychaeta have chlorocruorin or hemoerythrin
as blood pigments (both Fe containing pigments)
• Circulatory system much reduced or absent in
Hirudinea with coelomic fluid used for circulation
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Phylum Annelida- Nervous system
• Cerebral ganglia (brain) located above buccal
cavity
• connected to a subpharyngeal ganglion
• and a series of ventral segmental ganglia running
throughout body
Sense organs include:
touch receptors (tentacles and palps)
statocysts,
photoreceptors
mechanoceptors (vibration)
chemoreceptors that include ciliated slit
nuchal organs in head of most polychaetes.
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Classification of Annelida:
Class I. Polychaeta (many setae)
• marine mostly benthic habitat
• About 70% of all annelids
• Possess a minimum of one pair of eyes and anterior sensory
appendages
• Paired parapodia carrying acicula (chitinous support rods) and
many siliceous, chitinous or calcareous setae,
• Parapodia: paired outfoldings; function as locomotive and gas
exchange; Some species with overlapping elytra protective plates;
• Septa between anterior segments may be absent or perforated
especially in active burrowing spp. to allow this part to function as
proboscis (penetrating organ into sediment);
• Muscles include circular, longitudinal and oblique muscles;
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Nereis
Perinereis
A. Fireworm (Eurythoe spp);
B. Fan or Feather worm;
C. Calcarious tubes of Sedentary
polychaetes.
Ophryotrocha
Acrocirrus
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Polychaeta Reproduction & Life Cycle
• Asexual:
– fragmentation & regeneration of missing parts
– budding
• Sexual:
– worms are dioecious with gametes produced by special peritoneal tissue in
certain segments or most segments
– fertilization external in water
Some polychaetes undergo epitoky in preparation for sexual
reproduction. Male or female individual (atoke) in a tube or burrow
develops into or buds at its posterior end one or more epitokes
(specialized for sexual reproduction); epitokes detach, swim away and
commingle with other epitokes and discharge sperms or eggs for
external fertilization.
• Life cycle
– mostly as follows: fertilized egg---trochophore larva (wheel bearer), active
swimmer---adult.
– In some spp, fertilized eggs develop into juveniles within gelatinous mass or
brooding chambers that grow continuously to reach adult stage.
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Reproduction in Annelids
Asexual reproduction
by budding
Myrianida
epitoke formation
Trochophore larva
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Polychaeta Groups I
(Two groups based on mode of living)
Group Errantia
• Errant, active and mobile;
• Well developed parapodia for active oar-like
locomotion and eel-like movement on
substratum;
• Well developed head appendages including
palps, tentacles, and toothed or jawed
protrusible pharynx;
• Mostly carnivorous but some are suspension or
detritus feeders and others are omnivores;
• Most spp surface dwellers but some burrow &
live within substrates.
• Examples: Nereis, Harmothoe (have
overlapping elytra),
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Errant Polychaetes
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Polychaeta Groups
Group Sedentaria
• Sedentary living within simple
burrows or well constructed rigid
and protective tubes within
sediment
• Parapodia reduced, modified into
fan like shape for water movement
• Suspension or deposit feeders.
• Examples:
– Chaetopterus (in tube with two
openings),
– Arenicola (with gills),
– Sabella (with fan like anterior filaments
projecting from the tube)
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Classification of Annelida:
Class II. Clitellata
• Mostly in fresh water and moist terrestrial habitats with few marine
species
• Clitellum (specialized glandular epidermis surrounding certain segments
and functions in secreting mucus to help transfer sperms between
reciprocally copulating worms, secreting a cocoon where embryos
develop, and secreting albumin that embryos feed upon);
• No parapodia
• No sensory appendages
• Gas exchange by diffusion across moist body wall
• Monoecious with permanent gonads (ovaries and testes) in certain
segments
– Cross fertilization as a rule
– No trochophore larva in life cycle
– instead embryos develop within cocoons into juveniles that grow steadily into
adults.
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Clitellata Subclasses:
Subclass Oligochaeta & Subclass Hirudinea
Subclass Oligochaeta
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Mostly in freshwater and moist terrestrial habitats
About 6.5% are marine
Deposit feeders
Parapodia are lacking
Few setae in two sets per segment
Locomotion through peristaltic waves (continuous series of localized
contractions and relaxations of circular and longitudinal muscles) that help
in burrowing and moving.
Reproduction: Asexual & sexual:
-Asexual: by transverse fragmentation and regeneration of missing parts, or
by parthenogenesis (eggs develop without fertilization).
-Sexual by reciprocal:
alignment of two hermaphroditic worms
transfer of sperms for external cross fertilization of eggs
embryos develop in cocoon secreted by clitellum,
development of juveniles which grow into adults.
Example: Lumbricus (earthworm).
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Clitellata Subclasses:
Subclass Oligochaeta & Subclass Hirudinea
Subclass Hirudinea (leeches)
• mostly in freshwater or terrestrial moist habitats, few spp. in marine
habitat
• lack setae
• Lack head appendages
• Locomotion by looping aided by having anterior and posterior suckers,
longitudinal and circular muscles.
• No septa between segments although superficial and deep annuli
distinct
• coelomic space largely filled with mesenchyme
• Reduced or no circulatory system, coelomic fluid function as circulatory
medium;
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Connective mesenchyme tissue
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Clitellata Subclasses:
Subclass Oligochaeta & Subclass Hirudinea
Subclass Hirudinea (leeches) (Continued)
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Mostly spp. (75%) ectoparasitic blood suckers and rest
are predators on invertebrates; Blood suckers are mostly
equipped with 3-toothed jaws or protrusible proboscis
to feed on blood of vertebrates or invertebrates
– They secrete anticoagulant (hirudin)
– local anesthetic
– antibiotic substances
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Medical use is blood letting
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Reproduction: Only sexual by reciprocal copulation of
two hermaphroditic worms
Cross fertilization internal through direct transfer of
sperms or jabbing spermatophores through body wall.
Development occurs in cocoon where embryos develop
into juveniles that grow into adults and leave cocoon.
Example: Hirudo medicinalis (medicinal leech).
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