The world of Annelids_gallardo2028

John Marlon Gallardo
Krystel lyka Pastores
Cytel Mae Bayuca
Maricris Tungpalan

The Annelida
Segmented worms make up the Phylum Annelida.
The phylum includes earthworms and their relatives,
leeches, and a large number of mostly marine worms
known as polychaetes. Various species of polychaete are
known as lugworms, clam worms, bristleworms, fire
worms and sea mice.
Annelids can be told by their segmented bodies.
Polychaetes (meaning "many bristles") have, predictably,
many bristles on the body, while earthworms and leeches
have fewer bristles. There are about 15000 species of
annelid known today.

⋟ Typically, the external grooves correspond to to internal
partitions called septa, which divide the internal body space by a
series of compartments.
⋟ Most familiar examples of segmented worms are the common
earthworms or night crawlers, and the fresh water leech.
⋟ The more numerous and typical members of the phylum are marine,
crawling or hiding under rocks, or living in burrows, or in tubes, or in
the sediment.
⋟ The formidable bloodworm (Glycera), a intertidal worm with four
fanglike jaws at the anterior end.(red arrow)
⋟ The hallow fangs inject poison from venom glands into its prey.

Life History and Ecology
Annelids have radiated into a number of niches. Some are
parasitic, notably the leeches and myzostomarians; others filter-feed
Soils may harbor 50 to 500 earthworms per square
or prey on other invertebrates. However, probably the most
meter; they keep soils aerated, and their castings fertilize
the soil.
significant ecological role played by annelids is reworking of soil
and sediments. Many polychaetes and oligochaetes, and even a
few leeches, Most are earthworms burrowers that and constantly leeches
rework the sediment
through which they burrow; in addition, they may ingest and
excrete large quantities of sediments or soils. Robison (1987)
notes that some sandy beaches may harbor 32,000 burrowing
annelids per square meter, which collectively may ingest and
excrete 3 metric tons of sand per year. The tubes sticking up from
the sand in this picture, taken on a beach at Bahia de las Animas,
Baja California, give some idea of how common polychaetes can
be in such environments.
are hermaphroditic with both male and female
gonads. Polychaetes usually have separate sexes; many
polychaetes hatch into a particular type of planktonic
larva, the trochophore, which later metamorphoses into a
juvenile annelid. Some polychaetes, however, can
reproduce asexually, by budding.

1. Bilaterally symmetrical and vermiform.
2. Body has more than two cell layers, tissues and organs.
3. Body cavity is coelom, often divided by internal septa.
4. Body possesses a through gut with mouth and anus.
5. Body possesses three separate sections, a prosomium, a
trunk and pygidium.
6. Has a nervous system with an anterior nerve ring, ganglia
and ventral nerve chord.
7. Has a true closed circulatory system
8. Has no true respiratory organs
9. Reproduction normally sexual and gonochoristic or
hermaphoditic.
10.Feed a wide range of material.
11.Live in most environments..

NEREIS is a marine annelid belonging to class polychaeta. They in habit rocky and substranum.
Structurally, the animal exhibits a prostomium found above the mouth bearing a number of
tentacles, eyes, and palps. Posterior to the prostomium is the peristomium bearing a number of
cirri. The remaining body segments are identical, each bearing is lateral paropodia with bristle-like
projections, the setae. These parapodi are used for locomotion. The last segment is called
pygidium.
EARTHWORM this aquatic annelid belonging to class oligochaete inhabits moist
soil. Unlike Nereis the prostomium is not distinct. The body segments do not
process parapodia although there are few setae which project from dorsal and
ventral surface of the somites. In a mature specimen segments, 31-37 are swollen
forming an enlargement, the elithellum. This is associated with reproduction.
MEDICINAL LEECH this is a freshwater worm belonging to class hirudenea. The
body is dorso-ventrally flat and the segment do not possess setae or parapodia.
This worm is parasitic with a small anterior sucker surrounding the mounth and
a large posterior sucker for a temporary attachments to its host.

I. CLASS POLYCHAETA
Polychaetes are either “errant”---moving and
feeding actively, or “sedentary”--- with a passive
lifestyle.
 The basic body plan of an errent form is illustrated by
the sandworm nereis. The anterior and of nereis is
specialized to form “ head”, possessing two pair of
eyes and several pairs of sensory appendages. The
remainder of the body consists of a large number(100)
pairs or more of similar segments, each with a pair of
distinct lateral appendages are called parapodia. The
parapodium is a mascular highly mobile, and divided
into two lobes an upper, or dorsal,”notopodium”, and
lower or ventral “neuropodium”.

Each lobe bears a bundle of bristles, or satae. The satae, made of a
Parapodia and Setae
substance called chitin, are used in crawling or in swimming. Nereis is a
carnivore. Its food consisits of small live organisms, or fragments of dead
organisms, which it grasps by means of pair of powerful jaws located at the tip
of an eversible muscular pharynx. The food is ground up and digested as it
passes through successive parts of the straight, tubular gut. The undigested
residues discarded to the anus located at the posterior end.
Most other body systems are arranged on a, ”segmented plan”, which
means that structures performing a particular body functions are repeated in
each segment. Thus, for excretion each segment contains a pair of coiled,
ciliated tubes called nepridia. At one end the nepridial tube opens into the
spacious cavity called coelom between the body wall and the gut; at the end
it opens to the outside. There is well developed circulatory system. The blood,
which is red in color due to the presence of hemoglobin, circulates in blood
vessels. Gas exchange occurs between blood and sea water across the thin,
leaf-like lobes of the parapodia.

Parapodia – lateral extensions
supported by chitin
Setae – bristles secreted from the
distal ends of the parapodia
*Important for locomotion/ digging

Parapodia and Setae
See them work in action

*External Structure and
Locomotion
Prostomium- lobe that projects
dorsally and anterior to mouth
contains: eyes, antennae, paps
and nuchal organs
Nuchal organs: ciliated
sensory pits which are
chemoreceptors for food
detection

Locomotion
Peristomium- first body segment; surrounds the
mouth

Locomotion

*Feeding and the Digestive System
Digestive tract is a straight tube:
Pharynx- when everted can form a proboscis
Crop- storage sac
Gizzard- grinding
Intestine-long and
straight

*Feeding and the Digestive System
*Polychaeta can be:
*Predatory-usually burrow or live
in coral crevices; some can have
poison glands
*Herbivores
*Scavangers
*Filter feeders- tube dwelling

Examples of different worms and how they feed
Selective deposit feeders with
tentacles.
Filter feeders with radioles.

*Excretion
*Excrete ammonia
• Most of the excretory organs in annelids are active in
regulating water and ion balances
• Nephridia – excretory organs in annelids
• Two types of Nephridia
• Protonephridia- tubule with a closed bulb at one end and a
connection to the outside of the body at the other end.
• Metanephridia- open ciliated funnel (nephrostome) that
projects through an anterior septum into the coelom of an
adjacent segment

*Excretion
Osmoregulation and
waste removal
Metanephridia with
nephrostomes
open to coelomic
fluid.
Lead to
nephridioducts
which reabsorb
wanted
materials.
Waste released
through
nephridiopore.

*Gas Exchange and
Circulation
*Respiratory gases diffuse across body wall and parapodia
(increase surface area)
*Closed circulatory system
*Oxygen is carried by molecules called respiratory
Pigments- blood colorless, green or red
*Dosal aorta- propels blood from rear (posterior) to front
*Ventral aorta- propels blood from front to rear
*With Capillaries between the two aortas

*Nervous and Sensory
A pair of Subpharyngeal ganglia- mediates locomotor functions required for
coordination of distant segments.
Connects to
Circumpharyngeal connectives-run dorsoventrally along the pharynx
* By
*Ventral nerve cord with paired segmental ganglia in each segment; allows
escape response of segments
*Segmental ganglia- coordinate swimming and crawling movements in isolated
segments.
*2–4 pairs of eyes

Suprapharyngeal
ganglia
Circumpharyngeal
connectives
Subpharyngeal
ganglia
Segmental ganglia

* Reproduction and Regeneration
•All polychaetes can regenerate lost segments
•May have natural break points if grabbed by predators
(process called autotomy)
•Some reproduce by fission or budding
*Most sexually reproduce
*Most are dioecious
*External fertilization and trochophore larvae
*Swarming occurs in some species, where large numbers
of individuals join together to release sperm and/or
eggs.

Each body segment also has a pair of ganglia and three
or four pairs of nerves for receiving sensory input and
coordinating muscular activity. Ganglia in successive
segments are connected by means of longitudinal nerve
cords, so that nerve impulses can be transmitted back and
forth between each segment and the “cerebral ganglion” or
“brain” located in the head sexes are separate, although no
external characteristics distinguish males and females.
There are no permanent tetes or ovaries; rather, sperm and
egges develop from the lining of the body cavity during the
breeding season early spring , and fill the coelomic space.
They are released into the surrounding water by rupture of
the body wall.

*Reproduction and Regeneration
*Very few species copulate (most
external fertilization)
*Epitoky- formation of a reproductive individual (an
epitoke) that differs from the nonreproductive form of
the species (an atoke).
*Epitoke- body modified into 2 body regions;
anterior segments-normal maintenance; posterior
segments-enlarged & filled with gametes
*Example: Samoan palolo worm swarm
.

*In some species the epitoke breaks
free from the atoke, which stays
in the burrow
The common clam worm
Nereis succineain its atoke
form (above) and epitoke
form (below). Especially
note the enlarged
parapodia on the epitoke;
it uses these to swim and
release eggs or sperm.

*
In others, the epitoke is formed as
part of the body, and the whole
animal leaves to mate
Epitoke on the left,
atoke on the right

*3 Advantages of Swarming
Epitokes
1. Nonreproductive individuals remain safe below the
surface waters; predators cannot devastate an entire
population.
2. External fertilization requires individuals to be ready at
the same time. Swarming ensures large numbers of
individuals are in the right place at the right time.
3. Swarming of vast numbers of individuals for brief
periods provide a banquet for predators. But because it
is such a BREIF period, predators can only eat so much
with respect to the limits of their normal diets.
Predators can dine gluttonously and still leave epitokes
that will yield the next generation of animals.

II.CLASS OLIGOCHAETA
Olingochaetes, for example the earth worm
Lumbricus, commonly live in burrows in the soil,
although a few genera (for example Tubifex, Stylaria,
Aeolosoma) occur in freshwater. Earthworms and other
oligochaetes differ from the typical polychaete in
lacking sensory appendiges and parapodia; in possessing
fewer setae; in being hermaphroditic, having
permanent gonads, and requiring internal fertilization;
in depositing eggs in small capsules called cocoons; and
in stage.

*Have setae but fewer
*Lack parapodia- get in the way because of burrowing
*Prostomium- lacks sensory appendages
*External Features

Giant Blue Earthworm
Terriswalkeris terraereginae
mucin it releases is luminescent
Lives in rainforest in Australia

The material forming the cocoon is
secreted from a specialized area of the body
called the clitellum. Like polychaetes,
oligochaetes have well developed powers of
regeneration. Freshwater oligochaetes are
typically microscopic in size, earthworms
commonly attain a length of 11.8 in (30 cm) or
more. The giant earthworm of Australia (genus
Megascolides) measures more than 9.8 ft (3 m

Locomotion
Have both circular and longitudinal muscles
Move by antagonistic contractions of these muscles
Bulging and elongating body segments in waves cause
the worm to move forward
Small setae help anchor the worm
Small conical prostomium acts like a wedge while
burrowing, and soil is swallowed (important for
decomposition)

*Gas Exchange and
Circulation: same as
polychaetes
*Nervous and Sensory: same as
polychaetes but lack well-developed
eyes

*Freshwater
oligochaetes can
reproduce asexually
which is usually followed
by the regeneration of
missing segements.
*Reproduction

III.CLASS HIRUDINEA
The class Hirudinea comprises leeches, which
are mostly blood-sucking parasites of aquatic
vertebrates; some leeches are predators. The vast
majority of leeches live in freshwater habitats such
as ponds and lakes, while a few are semi-terrestrial
and some are marine. A leech has a
relatively small and fixed number (30-35) of body
segments, although its body has a large number of
superficial groove-like markings giving it the
appearance of more extensive segmentation. With
the exception of one small group satae.

*External Structures
*Lack parapodia and head
appendages
*Leeches are dorsoventrally
flattened and tapered
anteriorly
*Anterior and posterior
segments have suckers

*Have 34 segments
*External
Structures

*Have lost metameric partitioning,
resulting in single body cavity
*Coelomic sinuses replace blood vessels
in most leeches
*Complex musculature (four types of
muscles)
*Move in looping motion or swim with
undulations
*Locomotion

* Feeding and Digestive System
*Scavengers-fallen and decaying vegetation
*Mouth->muscular pharynx->esophagus
*Esophagus expanded form of stomach, crop ( thin-walled storage
structure), gizzard (muscular grinding structure).
*Calciferous glands-evaginations of esophagus wall that rids the
body of excess calcium absorbed by food; regulates pH
*Intestine-principle site of digestion and absorption

III. Class Hirudinea
Eyes are usually present, but there are no
sensory appendages or parapodia. The mouth is
located in the middle of an anterior sucker. A
posterior sucker is present at the opposite end. The
suckers are used for attachment to the substrate
during the characteristic looping movements, and
for attachments to the host during feeding. Blood
sucking leeches secrete saliva containing an anti-coagulant.
The stomach of the blood-sucking leeches
has many paired, sac like extensions for storing the
blood. Digestion of the blood proceeds very slowly.

*Excretion
*Oligochaetes use metanephridia for excretion of ammonia and urea
and for ion and water regulation.
*Chloragogen tissue- acts like a liver for amino acid metabolism
(deaminates amino acids into ammonia and urea); excess carbohydrates
converts into glycogen and water
Reproduction
•Monoecious
•Reproduce sexually via reciprocal fertilization-both worms exchange
sperm (can last 2-3 hours!)
•Cocoon of mucous and chitinous materials produced by clitellum
•Eggs, sperm, and food (albumen) deposited in cocoon where
fertilization takes place
•Young worms hatch from cocoon (no larvae)

III. Class Hirudinea
A blood-sucking leech needs to feed only occasionally,
and go for long periods between meals. Predatory
leeches feed on aquatic invertebrates such as snails,
worms, and insect larvae. Like Oligochaetes, leeches
are hermaproditic, and have permanent gonads,
internal fertilization, and a clitellum. The smallest
leeches are only about 0.2 inches ^^^5 mm^^long; the
largest reach is about . Inches ^^45cm^^ when fully
extended. Among the common North American genera
of freshwater leeches are glossiphonia, Haemopis, and
Placobdella. The medicinal leech, Hirudo medicinalis,
is a native to Europe

*Clitellum- secretes
mucus during copulation
and forms a cocoon
(girdle-like structure)
*External Features

•Nervous System
Temperature senses
•Excretion
10 to 17 nephridia
•Reproduction
Monoecious
Reproduce sexually ONLY
Clitellum present only in the spring

*
Slide credits…Gallardo2028

The world of Annelids_gallardo2028

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