ANNELIDS
Instructor: Almonther I. Alhamedi
The Islamic University of Gaza
Department of Biology
E-mail : mhamedi@iugaza.edu.ps
Web page :http://site.iugaza.edu.ps/mhamedi
GENERAL CHARACTERISTICS
 Segmentation
Septa between segments
Each segment is also known as a metamere
Each metamere has a parapodia with numerous
setae
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highly developed
GENERAL CHARACTERISTICS
Integument- epidermis is one cell layer with
mucous gland that secrete a moist cuticle.
 Muscle- longitudinal and circular muscles Each
segments muscles are independent of the other
segments.
 Digestive- complete, complex, with typhlosole
for absorption and chloragogen cells acting as
digestive gland and excretory cells. As the liver
function.
 Excretory- a pair of nephridia per segment.
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GENERAL CHARACTERISTICS
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Respiratory -through skin, some through
parapodia; tubeworms have gills.
Circulatory- closed system, use hemoglobin as
oxygen carrier.
Nervous- dorsal brain; ventral, double, solid
nerve cord, with ganglia in each segment.
Endocrine- hormones secreted by nervous system.
Annelids are to be found in marine, fresh-water and
terrestrial habitats.
Annelids are hermaphrodites
The larva is the trochophore.
Coelomate.
CNS of preoral ganglia ‫ عقدة قبلفمية‬linked by connectives
to a pair of ventral ganglionated cords.
CLOSED VERSUS OPEN CIRCULATORY SYSTEMS
HYDROSTATIC
SKELETON
Earthworm
Phylum Annelida
ANNELID BODY PLAN
Setae
PHYLUM ANNELIDA
Class
Polychaeta
Marine worms
Nereis
class
Oligochaeta
Subclass
Hirudinae
earthworms
Leeches
Lumbricus
Hirudo
CLASS
POLYCHAETA
Approximately 63% of all annelids species are placed
in the class Polychaeta and mostly marine.
 Polychaeta possess at least 1 pair of eyes and at least
1 pair of sensory appendages (tentacles) on the
anterior most part of the body (the prostomium).‫قبلفم‬
 The body wall is extended laterally into a series of
thin, flattened outgrowths called parapodia
 Parapodia function in:
1- Gas exchange between the worm and its
environment.
2- Locomotory function in many species due to the
presence of chitinous support rods called acicula
‫(االبر‬Fig. 13.3a).
3- In addition, siliceous, chitinous, or, more rarely,
calcareous bristles called setae ‫شويكات‬protrude from
each parapodium
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POLYCHAETE ANATOMY
POLYCHAETE ANATOMY (CROSS SECTION)
Polychaete Larvae
class Oligochaeta
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Approximately 3,500 oligochaete species have been
described. Only about 6.5% of oligochaete species are
marine, most are found in fesh-water or terrestrial habitats.
The common earthworm, Lumbricus terrestris, ‫لومبريكاس‬
‫األرض‬is a familiar example (Fig. 13.12a.
Oligochaetes have more streamlined appearance compared
with most polychaete annelids.
parapodia are lacking and the anteriormost region of the
body, the prostomium, lacks sensory structures, such as eyes
and tentacles.
Oliogchaetes do have setae, but the setae are less densely
distributed along the body.
Oligochaete Excretory System
CLASS
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HIRUDINEA
includes the leeches, and has approximately 500 to
630 described species.
Most leeches occupy freshwater or terrestrial
habitats; only a small proportion from the species is
marine.
There are no parapodia and no setae.
-(Fig. 13.15b and 13.16).
-The body is generally not separated into
compartments by septa, and the continuous coelomic
space is largely filled with connective tissue, or
mesenchyme (Fig. 13.17).
Leeches locomote over solid substrates by using
suckers as temporary anchores.
These suckers are formed from groups of segments at
the body’s anterior and posterior ends (Fig. 13.16 and
13.18).
LEECHES
Leeches are generally ectoparasitic, feeding either on the
blood of other invertebrates or, more commonly, on the
blood of vertebrates.
 Many parasitic species possess 3 toothed jaws within the
mouth; leech uses these jaws to make an incision in the
host. Other species have a protrusible proboscis, through
which blood is removed from the host.
 An application of Hirudo medicinalis, the medical leech,
help in 2 ways:
1-Drains off the excess blood from the finger,
2-Injects an anticoagulant-hirudin-‫مادة مضادة للتجلط‬that keeps
the blood flowing out from the bite-wound long after the
sated leech has dropped off.
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Hirudo medicinalis
LUMBRICUS
clitellium
dorsal
ventral
Lumbricus
EARTHWORM
DISSECTION
Cross section
Return to taxonomy
EARTHWORM CROSS SECTION