Download Annelids

Phylum Annelida
the segmented worms
Annelids - segments
• Animals that have many segments
– Include earthworms, leeches and marine polychaetes.
• Most annelids have chitin-reinforced bristles --setae
on each side (to provide movement).
• Oligochaetes – few e.g. earthworms
• Polychaetes – many bristles per segment
• Provide evolution of regional specializations where
some segments undergo modification to take on new
functions. e.g. leeches have suckers at both ends and
polychaetes have elaborate head and segments `
closely resembling feet’.
Annelida Characteristics
Triploblastic
Organ level of organization
Bilateral Symmetry
Cephalization
Eucoelomate
Different Body Cavities
Acoelomate
No body cavity
ectoderm
mesoderm
Gut
endoderm
Different Body Cavities
Pseudocoelomate
Have a “false” body cavity that is surrounded on ONE side only by mesoderm
ectoderm
pseudocoelom
mesoderm
Gut
endoderm
Different Body Cavities
Eucoelomate
Have a “true” body cavity that is completely surrounded by mesoderm
ectoderm
coelom
mesoderm
Gut
endoderm
Annelid Characteristics
the coelom
ectoderm
• is a closed, fluid filled cavity that
surrounds
the gut
• the fluid within acts as a circulatory system
• mesodermal membranes (mesenteries)
suspend organs in the coelom
Annelida Characteristics
Protostome
Development is characterized by:
• blastopore becomes the mouth
Mouth Formation
Blastopore becomes the mouth and the anus
forms secondarily
Future anus
blastopore
archenteron
(primitive gut)
mouth
Annelida Characteristics
Metamerism
The body is made up of serially repeating,
coordinated segments called metameres that are
separated from one another by septa.
•Each metamere contains sets of repeating
organs
e.g. gut, blood vessels, nerve cord, excretory
organs
Metamerism
septa
FEEDING
– Digestive tract is a long tube extending from
mouth to anus
– Muscular pharynx is very diversified in annelids
(can include crop and gizzard similar to birds)
– Some have sharp teeth.
– Leeches use pharynx to suck blood and tissues
from host
– Some aquatic annelids are filter feeders.
Annelid RESPIRATION
• mainly by diffusion
•Aquatic annelids breath through gills (feather
duster worms)
Some use diffusion through skin
(skin must stay moist)
• Class Polychaeta often has specialized structures for
gas exchange
(e.g. parapodia, gills)
INTERNAL TRANSPORT
– Closed circulatory system with 2 blood vessels
running the length of their bodies (dorsal and
ventral)
– In each segment, smaller ring vessels supply
blood from the main vessels to organs.
– In earthworms, some of the ring vessels work like
hearts (pumping blood to the rest of the body)
NERVOUS SYSTEM
– Some have well developed nervous system
– Ventral nerve cord runs the length of the body in
earthworms.
– Free-living marine annelids have best developed
sense organs (balance organs, chemical receptors
and eyes).
– Earthworms have no specialized sensory cells.
MOVEMENT
– Two major muscle groups (longitudinal and
circular)
– (Nematodes only have longitudinal muscles)
REPRODUCTION
– Most reproduce sexually
– Earthworms have structure called a clitellum
which secretes a mucus ring into which eggs and
sperm are released during copulation.
Annelida Characteristics
EXCRETION
• excretion is
accomplished by organs called
nephridia (singular nephridium)
Skeletal System
• fluid in coelom acts as a hydrostatic skeleton
Phylum Annelida
Class Polychaeta
Class Oligochaeta
Class Hirudinea
Class Polychaeta
Class Polychaeta
• Poly = Many
• Chaeta = Bristles
• Aquatic worms with bristles or projections on either
side of the segments
Class Oligochaeta
Class Oligochaeta
• Oligo = Few
• Chaeta = Bristles
• Includes earthworms, burrowing worms
Class Hirudinea
Class Hirudinea
Leeches: _external parasites_
• Have powerful suckers at each body end
• Produce an anti-coagulant (prevents blood from
clotting) so that they can continue to drink the host’s
blood.
• Leeches can swallow up to 10X their weight in blood
and can survive off one meal for a whole year!
• Often used for medical purposes.
Class Polychaeta
Class Polychaeta
• all marine
• this class contains 2/3 of all known Annelids
• have a well developed head with specialized sense
organs
Class Polychaeta
• have many setae (chitonous bristles secreted by the
epidermis)
(Poly = many, chaeta= setae)
• these setae are arranged in bundles on paddle-like
appendages called parapodia
setae
Class Polychaeta
Parapodium
setae
The parapodia function in gas exchange,
locomotion, and feeding.
Class Polychaeta
Tagmatization (tagmosis)
• the
fusion and specialization of
formerly metameric segments
Class Polychaeta
Many are filter-feeders with specialized
structures
Class Polychaeta
Many are predatory with specialized
structures
Class Polychaeta
Many construct their own homes out of
CaCO3 or sand debris and mucous
Class Polychaeta
Reproduction
• usually dioecious
• no permanent sex organs; gametes are shed into coelom
• fertilization is usually external
• indirect development  trocophore larvae
Class Polychaeta
Epitoky
• In some species, the rear portion of the worm (“epitoke”: carries
the eggs or sperm), breaks off from the body and swims to the
surface to reproduce. The remaining benthic worm (“atoke”)
continues to feed and grow and will eventually produce new
epitokes.
• In other species, there are pelagic individuals that resemble
epitokes but the entire individual swims to the surface where the
body wall ruptures, filing the water with eggs and sperm.
• To synchronize these spawnings,
this swarming behavior is usually
triggered by the full moon.
Ecology
• Polychaetes often have effective
defense strategies:
• some have tubes to hide in
• some have vicious jaws
• some have modified “stinging” setae
a fireworm
Ecology
• Some Polychaetes have a mutualistic relationship
with their host
• for example, many scaleworms are found near, or
in the mouth, of brittlestars, starfish, and sea
urchins.
• The scaleworm eats its host’s leftovers and with
its vicious jaws, it will attack any predator trying to
eat it’s host.
Class Oligochaeta
Class Oligochaeta
• terrestrial, freshwater and marine
• have few setae (Oligo = few, chaeta = setae)
• usually feed on detritus
(decaying organic matter)
• have specialized digestive system to obtain the
maximum amount of nutrients out of the detritus
(e.g. typhlosole, gizzard, crop…)
Class Oligochaeta
typhlosole• infolding of the dorsal side of the intestine
• increases surface area for absorption of
nutrients
typhlosole
gut
Class Oligochaeta
Locomotion
Circular muscle
contraction
Longitudinal
muscle
contraction
Class Oligochaeta
Reproduction
• usually monoecious
• cross-fertilize by
exchanging sperm
clitellum
testis
Ecology
• Earthworms are essential soil aerators
• If all the material ever moved through earthworms was piled up, the heap
would rise 30miles , more than 5 times the height of Mount Everest!!
• Worm Grunting:
A saw or leaf spring of a pick-up
stob
Class Hirudinea
Class Hirudinea
• usually freshwater but there are some marine
and terrestrial species
• no septa between metameres
• no setae
• have 2 suckers
Class Hirudinea
• have an extendable proboscis for feeding
Class Hirudinea
• usually have a fixed number of segments (34)
• each metamere consists of several annuli
(think accordion)
1 metamere
annuli
Class Hirudinea
Locomotion
Lack septa between
metameres, so they are
incapable of moving like
Oligochaetes.
Instead, they use their
anterior and posterior
suckers to move.
Class Hirudinea
Reproduction
• usually monoecious
• cross-fertilize by
exchanging sperm
Ecology
• Although some leeches are parasitic blood suckers (can
be temporary or permanent), many are predators.
Ecology
• Leeches have been used medicinally since the 19th
century.
• Currently they are used to increase blood flow
following reconstructive surgery
• Hirudin is a powerful anticoagulant that is found in
the salivary glands of leeches
How do the Annelids fit in?
Oligochaeta
Hirudinea
Polychaeta
Nematoda
Platyhelminthes
Porifera
Rotifera
Nemertea
Cnidaria
eucoelomate
protostome
unknown
common ancestor