Download Major Divisions of Life

Phylum Annelida
The Segmented Worms Ch 11
Annelida Characteristics
Triploblastic
Organ level of organization
Bilateral Symmetry
Cephalization
Eucoelomate
Eucoelomate
Have a “true” body cavity that is completely surrounded
by mesoderm
ectoderm
coelom
mesoderm
Gut
endoderm
Annelid Characteristics
the coelom
• is a closed, fluid filled cavity that surrounds
the gut
•mesodermal membranes (mesenteries)
suspend organs in the coelom
Annelida Characteristics
Protostome
Development is characterized by:
• blastopore becomes the mouth
• Spiral / determinate cleavage
• Schizocoely
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. blood vessels, nerve cord, excretory
organs
Metamerism
septa
Annelida Characteristics
Nervous system
• 2 cerebral ganglia
• a ventral nerve cord with 2 ganglia per metamere.
• In some species, sensory organs such as eyes, palps,
and tentacles have arisen
Annelida Characteristics
Locomotion
• both longitudinal and circular muscles
• most have chaetae [setae] (chitonous bristles secreted
by the epidermis) that aid in locomotion and burrowing
Skeletal System
• fluid in coelom acts as a hydrostatic skeleton
Annelid Characteristics
Gas exchange
• mainly by diffusion
• Class Polychaeta often has specialized structures
for gas exchange
(e.g. parapodia, gills)
Annelid Characteristics
Digestive System
• complete
• regional specialization
Annelid Characteristics
Circulatory System
• closed circulatory system composed of blood vessels
(some of which are contractile and act as “hearts”)
• some circulation is also accomplished by the
coelomic fluid
Annelid Characteristics
Excretion
• excretion is accomplished by organs called
nephridia (singular nephridium)
Reproduction
• predominantly sexual
Phylum Annelida
Class Polychaeta
Class: Clitellata
Subclass: Oligochaeta
Subclass: Hirudinea
Class Polychaeta
Class Polychaeta
• most marine; about 30 species that are freshwater
and brackish water in the US.
• this class contains 2/3 of all known Annelids
• have a well developed head with specialized sense
organs
Class Polychaeta
• have many chaetae [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
chaetae
The parapodia function in gas exchange,
locomotion, and feeding.
Parapodia
are biramous
Class Polychaeta
Tagmatization (tagmosis)
• the
fusion and specialization of
formerly metameric segments
Class Polychaeta
Many are filter-feeders with
specialized structures
Terebellids with tentacles
that creep over the
surface of the substratum
and accumulate food
Class Polychaeta
Many are predatory with
specialized structures: Jaws
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.
• To synchronize these spawnings,
this swarming behavior is usually
triggered by the full moon.
Polychaetes Swarming
Class Polychaeta
Reproduction
• asexual
Epitokes
Symbiotic relationships
•Many scaleworms are found near, or in the
mouth, of brittlestars, starfish, sea urchins,
and molluscs.
• The scaleworm eats its host’s leftovers and
with its vicious jaws, it will attack any
predator trying to eat it’s host.
Subclass Oligochaeta
Subclass Oligochaeta
• terrestrial, freshwater and few 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…)
Subclass Oligochaeta
typhlosole• infolding of the dorsal side of the intestine
• increases surface area for absorption of
nutrients
typhlosole
gut
Subclass Oligochaeta
Reproduction
• usually monoecious
• cross-fertilize by
exchanging sperm
clitellum
testis
Earthworms Secret Cocoons
Where They Store Their Eggs!
Ecology
• Earthworms
are essential soil aerators in
terrestrial and aquatic habitats
• If all the material ever moved through
earthworms was piled up, the heap would
rise 30 miles , more than 5 times the height
of Mount Everest!!
What is the most exciting thing
about earthworms?
What is the most exciting thing
about earthworms?
The Giant Gippsland earthworm, Megascolides australis can
reach lengths of nearly 4 meters, and the Australian earthworm
Terriswalkeris terraereginae can get to 2 meters in length and
the mucin it releases is luminescent!
What is the most exciting thing
about earthworms?
The Microchaetus rappi more commonly know as the Giant
South African Earthworm to over 20 feet long!