Transcript Phylum ANNELIDA

ANNELIDA
Segmented Worms
Phylum ANNELIDA
• means little ring
Over 9K species
Bilateral symmetry
More advanced nervous (ganglia) and closed
circulatory systems
Body segmentation termed metamerism (body
divided internally as well)
Most have tiny bristles or setae which mainly aid
in locomotion
Group contains earthworms, leeches and their
kin
Classification: initially by setae arrangement and
presence of a clitellum (packsaddle)
External Anatomy
BODY PLAN
• 1. usually a prostomium (lip)(mouth derived from
blastophore) at 1 end and pygidium (anus) at the
other
2. many septa (walls) separate segments
internally
3. usually coelom serves as a hydrostatic
skeleton (the use of body cavity fluids, confined
by the body wall, to give support)
4. may have a fixed number of segments
(leeches)
5. segments often added just before the anus
6.tagmatization – the specialization of body
regions (ex. Head – feeling sensory, thorax –
locomotion, abdomen – visceral)
• Annelids are
segmented
worms. Their
coelom is fluidfilled and serves
as a hydrostatic
skeleton against
which muscles
can pull. Septa
divide the body
into individual
compartments.
There is a closed
circulatory
system, ventral
nerve cord, and
there may be
appendages on
the segments.
Introduction to the Polychaeta
the bristleworms
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Class POLYCHAETA
• means many long hairs
> 5-10cm long
> largest (over 5K species) and most primitive class
> mostly marine with some being bright red or green
> eaten by fish, crustaceans, hydroids and others
> paired appendages ( parapodia (are found beside little foot) –
paired lateral extensions on each segment of polychaetes, may be
used for swimming, crawling, and burrowing) but no clitellum
> many crawl, burrow or live in tubes
> have setae (bristles) at the ends of the parapodia
> protomium – before mouth, numerous sensory organs, eyes,
antenna, palps, ciliated pits and grooves, called nuchal organs
> peristomium – first body segment
> cuticle – protective coating
Ex: Arenicola Amphitrite Sabella Chaetopterus
Specimen of Arenicola marina with
proboscis everted. Image 17 cm
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FEEDING
straight tube
crop – storage sac
gizzard – grinding organ
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RESPIRATORY
Most gases diffuse across the body wall
Closed circulatory system
Blood – colorless, red, green depends on long intestines respiratory
pigment
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NERVOUS & SENSORY
ganglia – nerves run dorsoventrally
…...along either side of pharynx
2-4pairs of eyes
most react negatively to increased light intensity
fanworm reacts with decreased light intensity
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EXCRETE
Regulating water
Ammonia
Some across body wall
Excretory organs called Nephrida
REGENERATION
• All polychaetes have remarkable powers
of regeneration. They can replace lost
parts, and some species have break
points that allow worms to sever
themselves when a predator grabs them.
Lost segments are later regenerated.
REPRODUCTION &
DEVELOPMENT
• asexual (budding or fission) , sexual reproduction is more common.
Most dioecious
Gametes are shed into the coelom, where they mature. Mature
female worms are often packed with eggs. Gametes may exit
worms by entering nephrostomes (the excretory organ of the
embryo. The embryonic tube from which the kidney develops.
Tubular osmoregulartory and excretory organ of many invertebrates.
Functions in excretion, osmoregulation, or both) of metanephridia
(an excretory organ in many invertebrates. It consists of a tubule
that has one end opening at the body wall and the opposite end in
the form of a funnel-like structure that opens to the body cavity) and
exiting through the nephridiopore (The opening to the outside of a
nephridium. An excretory opening in invertebrates), or they may be
released, in some polychaetes, after the worm ruptures.
>Fertilization is external in most polychaetes, few species copulate.
>Epitoky – formation of a reproductive individual
>Atoke - nonreproductive form of the species
CLAMWORMS Nereis
clamworm
1. marine benthic " sand worms "
2. crawl out of their burrows at nite to feed
3. have about 200 segments, 4 eyes, 4 tentacles
4. swim with undulatory movements
5. seize little animals with chitinous jaws
Other polychaetes : Scale worms
Polynoe
Fireworms Hermodice
Parchment worm: Chaetopterus a tube worm
with fans
Clam worm
(Nereis spp.)
Clam worms are free
swimming, segmented
worms with four pairs of
tentacles and one pair of
antennae. Each segment
has a pair of bristly,
paddle-like appendages
(parapodia) that enable
them to swim in the water
or crawl along the
seafloor. Clam worms
feed on algae and other
invertebrates that they
find by burrowing in the
sand or mud. They are
food for bottom feeding
fish and crabs.
Bearded
Fireworm
• gladiators
Parchment worm - Chaetopterus
variopedatus
Parchment Worm
Distribution in Britain
and Ireland
Chaetopterus sp.
Parchment worm
Class OLIGOCHAETA
• • means few long hairs
1. earthworms have setae, lack parapodia
2. Lumbricus terrestris is the earthworm
burrow in moist rich soil
most active at nite
3. most are scavengers on leaves and animal
matter
4. series of segments in the anterior half of an
oligochaete is usually swollen into a girdlelike
structure called clitellum, this secretes mucus
during copulation and forms a cocoon.
5. food passage from the mouth > esophagus >
crop > gizzard
Class OLIGOCHAETA
• 6. blood has hemoglobin and respiration is by
diffusion
7. so-called brain is a pair of cerebral ganglia
8. fast escape is due to giant axons that increase
conduction rate
9. sense organs include skin photoreceptors,
chemoreceptors and tactile nerve endings (also a
pair of setae per segment )
10. cuticle covers the body
11. nitrogenous wastes include ammonia and urea.
12. chloragogen tissue – similar to the vertebrate
liver, it is an amino acid metabolism, it converts
ammonia to urea, and excess carbs into glycogen
and fat
EARTHWORM BEHAVIOR /
REPRO.
• 1. must sense soil texture, acidity and calcium
content
2. some learning ability (Ex: to avoid shock)
3. monoecious /segments 9-15
4. usually mate at nite during warm moist
weather
5. a tough band cocoon forms around the
clitellum where fertilization occurs and hatching
occurs
Freshwater Oligochaetes usually smaller but
with larger setae
6. seminal vesicles, sites for maturation and
storage of sperm prior to their release
• 7. seminal receptacles – receives sperm during copulation.
8. during copulation two worms line up facing in opposite
directions, with the ventral surfaces of their anterior ends in
contact with each other. This orientation lines up the clitellum
of one worm with the genital segments of the other worm. A
mucous sheath that the clitellum secretes envelops the
anterior halves of both worms and holds the worms in place.
Some have penile structures, which help maintain contact
between worms. The sperm duct releases sperm.
Copulation lasts two to three hours, during which both worms
give and receive sperm. The clitellum forms a cocoon for the
deposition of eggs and sperm. The cocoon consists of
mucoid and chitnous (exoskeleton) materials that encircle the
clitellum. The clitellum secretes a food reserve, albumen,
into the cocoon, and the worm begins to back out of the
cocoon. Fertilization occurs in the cocoon. Hatching occurs
in one to a few weeks.
9. freshwater oligochaetes also reproduce asexually usually
by regeneration
Ex: Aeolosoma Nais Stylaria Dero Chaetogaster
Oligochaeta
Anterior end
Posterior end
Dorsal View of Anterior End
Ventral View of Anterior End
Class HIRUDINEA The Leeches
• means leech ; mostly freshwater predators
1. usually 1 to 12 inches long and any of 4 colors
2. clitellum only during the breeding season and are
monoecious
3. setae replaced by suckers because they are fluid
feeders and bloodsuckers
4. fixed number of somites / segments, usually 34, annuli
– secondary divisions, on each true segment
5. most freshwater species are active predators or
scavengers
6. freshwater species attack cattle, humans and others
7. land species feed on insect larvae, earthworms and
slugs or even climb to reach birds and mammals
Cont.
8. the fluid feeders prefer blood and have an anticoagulant
in their " saliva " to keep the flow going until they have
gorged and swollen
9. salivary glands secrete an anticoagulant called hirudin
that prevents blood from clotting
10. can increase their body mass 2 – 10 times
11. gas exchange is through the body wall
12. all leeches reproduce sexually and are monoecious,
none are capable of asexual reproduction or
regeneration
Ex: Hirudo Placobdella Macrobdella