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PHYLUM ANNELIDA Segmented Worms
Triploblastic
Mouth and Anus
True coelum
Bilaterally symmetrical
External Parasite/Soil
Closed circulatory system
www.nsf.org www.homestead.com
Annelida
• Annelids have bodies composed of a series of
fused rings
• The phylum Annelida is divided into three
classes:
– Oligochaeta (earthworms and their relatives)
– Polychaeta (polychaetes)
– Hirudinea (leeches)
Annelida: Oligochaetes
• Oligochaetes (class Oligochaeta) are named for relatively sparse chaetae, bristles made of chitin
• They include the earthworms and a variety of aquatic species
• Earthworms eat through soil, extracting nutrients as the soil moves through the alimentary canal
Earthworms are hermaphrodites but cross-fertilize
http://en.wikipedia.org/wiki/File:Mating_earthworms.jpg
Fig. 33-22
Epidermis
Circular muscle
Longitudinal muscle
Dorsal vessel
Chaetae
Intestine
Nephrostome
Fused nerve cords
Ventral vessel
Metanephridium
Septum (partition between segments)
Coelom Cuticle
Anus
Metanephridium
Crop
Intestine
Gizzard
Ventral nerve cord with segmental ganglia Blood
vessels
Subpharyngeal ganglion
Mouth Cerebral ganglia
Pharynx
Esophagus
Clitellum
Giant Australian earthworm
Annelida: Oligochaetes: Earthworm dissection
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/animal%20diversity/protostomes/loph
otrochozoans/lophotrochozoans.htm
Members of class
Polychaetes have paddle-like
parapodia that work as gills
and aid in locomotion
Parapodia
Bristle Worms
Members of class
Hirudinea are blood-
sucking parasites, such
as leeches
PHYLUM NEMATODA
Cuticle surrounds body
Triploblastic
Mouth and Anus
Pseduocoelum
Bilaterally symmetrical
Internal Parasite/Soil
Tube within a tube
Lack a circulatory or respiratory system
“It’s a nematode world” E. O. Wilson
Nematodes, or roundworms, are found in most
aquatic habitats, in the soil, in moist tissues of
plants, and in body fluids and tissues of animals
EO Wilson on TED talks March 2007
There are more than 15,000 species of
roundworm named.
The pseduo-coelum is most likely a
secondarily derived character, and is
probably not a useful phylogenetic
characteristic and recent research shows
that they are most likely most closely
related to Arthropoda.
Wallace, Ricci, & Malone 1996 interactive key to the nematodes
They have an alimentary canal, but lack a circulatory
system
http://www.bumblebee.org/invertebrates/Nematoda1.htm
Reproduction in
nematodes is usually
sexual, by internal
fertilization and the sexes
are distinct.
Nematodes exhibit
Sexual Dimorphism –
our Ascaris are quite
large and therefore
female.
Ascaris lumbricoides is the most common human
nematode parasite but many other plague humans
around the world. Filariasis is a general name for
nematodes that reside in lymph and connective
tissue.
Both Loa Loa and
Onchoceriasis infect
the fluid inside the eye
Wucherieria bancrofti
block lymph nodes of
infected people and
cause edema.
Encysted juveniles Muscle tissue
Juveniles of the parasitic nematode Trichinella spiralis
encysted in human muscle tissue (LM)
If all the matter in the universe
except the nematodes were swept
away,
our world would still be dimly
recognizable...
-N.A. Cobb from Nematodes and
Their Relationships, 1915
The virtual nematode
Meet Mephisto - The worm that rules the
underworld - Discover magazine
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