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 or prey on other invertebrates. However, probably the most

significant ecological role played by annelids is reworking of soil

and sediments. Many polychaetes and oligochaetes, and even a

few leeches, are burrowers that constantly 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.

Soils may harbor 50 to 500 earthworms per square

meter; they keep soils aerated, and their castings fertilize

the soil.

Most earthworms and leeches

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

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 and Setae

Parapodia – lateral extensions supported by chitin

Setae – bristles secreted from the distal ends of the parapodia

*Important for locomotion/ digging

Parapodia and SetaeSee them work in action

*External Structure and Locomotion

Prostomium- lobe that projects dorsally and anterior to mouth

contains: eyes, antennae, papsand nuchal organs

Nuchal organs: ciliated sensory pits which are chemoreceptors for food detection

*External Structure and Locomotion

Peristomium- first body segment; surrounds the mouth

*External Structure and 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.

*Nephridia

*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.

*External Features

*Have setae but fewer

*Lack parapodia- get in the way because of burrowing

*Prostomium- lacks sensory appendages

Giant Blue Earthworm

Terriswalkeris terraereginae

mucin it releases is luminescent

Lives in rainforest in Australia

II.CLASS OLIGOCHAETA

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

II.CLASS OLIGOCHAETA

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

Locomotion

*Gas Exchange and Circulation: same as polychaetes

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

*Reproduction

*Freshwater oligochaetes can reproduce asexuallywhich is usually followed by the regeneration of missing segements.

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

*External Structures

*Have 34 segments

*Locomotion

*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

* 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)

Eggs

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

*External Features

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

•Nervous SystemTemperature senses

•Excretion10 to 17 nephridia

•ReproductionMonoeciousReproduce sexually ONLYClitellum present only in the spring

*

Slide credits…Gallardo2028