PHYLUM ANNELIDA

By:J.Q

Phylum Annelida

• (L. annelus, little ring, ida, pl. suffix) consists of the segmented worms

• 15,000 species• worms whose bodies are divided into similar segments,

(metameres) arranged in linear series and externally marked by circular rings called annuli

• Sometimes called “bristle worms” because most annelids bear tiny chitinous bristles called setae

Functions of Setae

- terrestrial annelids – locomotion

- aquatic forms - swimming

Body Plan:

• The annelid body typically has a two-part head, composed of

a prostomium and a peristomium followed by a segmented

body and a terminal portion called the pygidium bearing an

anus

• Peritoneum (a layer of mesodermal epithelium) lines the body wall of each compartment, forming dorsal and ventral mesenteries that cover all organs

• Hydrostatic skeleton

– coelom is filled with fluid.

Class Polychaeta

Class Polychaeta

• Polychaeta (Gr. polys, many, chaite¯, long hair) with more than 10,000 species

• Many polychaetes are euryhaline.• Polychaetes differ from other annelids in having a well differentiated

head with specialized sense organs; paired appendages, called parapodia,

-  paired appendages of polychaete that function in locomotion and breathing.

Polychaetes are often divided into two morphological groups

based on their activity:- Sedentary polychaete- Errant polychaete

Sedentary polychaete

- spend much or all of their time in tubes or permanent burrow

Errant Polychaete

- swim, crawl over the ocean bottom, or tunnel through surface sediments.

Form and Function:• the prostomium, which may or may not be retractile and which often

bears eyes, tentacles, and sensory palps - The peristomium surrounds the mouth and may bear setae,

chitinous jaws.

Nutrition :- digestive system consists of a foregut, a midgut, and a hindgut.

- Foregut - includes a stomodeum, a pharynx, and an anterior esophagus.

- Midgut - secrete digestive enzymes but absorption takes place toward the posterior end.

- Hindgut - connects the midgut to the exterior via the anus, which is on the pygidium.

Circulation and Respiration:• parapodia and gills serve for gaseous exchange in various species. • circulatory pattern varies greatly• In Nereis blood flows between these two vessels via segmental

networks in the parapodia, septa, and around the intestine. • In Glycera the circulatory system is reduced and joins directly with

the coelom. Septa are incomplete, and thus the coelomic fluid assumes the function of circulation.

Excretion: - either protonephridia or metanephridia.

Reproduction:• Dioecious – separate sexes

 

Largest Polychaete

-Eunice aphroditois, the Bobbit worm(can grow upto 3 meters)

• Class Oligochaeta

Class Oligochaeta

• 3000 species of oligochaeta• include the familiar earthworms and many species that live in

freshwater.• Most are terrestrial or freshwater forms, but some are parasitic

Ex. Chaetogaster limnaei

Forms and Body Function:- Earthworms use peristaltic movement: Contractions of circular

muscles in the anterior end lengthen the body, pushing the anterior end forward where it anchors.- Differ from polychaetes, no parapodia

Form:

Circulation and Respiration : - Have a double transport system: coelomic fluid and a closed

circulatory system. • coelomic fluid – carries food, wastes, and respiratory gases.• closed circulatory system – which includes capillary systems in the

tissues.

Nutrition:• Most are scavengers.• - feed mainly on decaying organic matter, bits of leaves and

vegetation, and animal matter.

Excretion:• bears a pair of metanephridia. • - occupies parts of two successive segments :ciliated

funnel & Nephrostome

Reproduction and Development :

- Earthworms are monoecious (hermaphroditic).

• Class Hirudinida

Class Hirudinida

• Leeches are between 2 and 6 cm in length, but some, including “medicinal” leeches, reach 20 cm.

• The giant of all is the Amazonian Haementeria (Gr. haimateros, bloody) (which reaches 30 cm!!!!!)

• flattened dorsoventrally• Hermaphroditic

Form and Function:• Leeches are more highly specialized than oligochaetes.

- they don’t have setae but have sucker for attachment and for sucking blood.• Leeches crawl with looping movements of the body, by attaching first

one sucker and then the other and pulling the body along the surface.

Form:

Nutrition:• Leeches are popularly considered parasitic, but many are

predaceous.

1. Fresh water leech

- active predators or scavengers equipped with a proboscis that can be extended to ingest small invertebrates or to take blood from cold-blooded vertebrates.

Ex. medicinal leech, Hirudo medicinalis

2. Terrestrial leech –

- feed on insect larvae, earthworms, and slugs,which they hold by an oral sucker while using a strong sucking pharynx to ingest food.

Ex. Haemadipsa sp.

3. Marine Leech

- Common hosts Fish, sharks and rays that live on exterior surface, fins, anus, gill cavity, and spiracle.

Ex. Stibarobdella loricata

Circulation:• The coelom of leeches has been reduced by the invasion of

connective tissue and, in some, by a proliferation of chloragogen tissue, to a system of coelomic sinuses and channels.

Reproduction:• Leeches are hermaphroditic but cross-fertilize during copulation.

1. 1.Sperm are transferred by a penis or by hypodermic impregnation (a spermatophore is expelled from one worm and penetrates the integument of the other).

2. 2.After copulation their clitellum secretes a cocoon that receives eggs and sperm.

3. 3. Leeches may bury their cocoons in mud, attach them to submerged objects, or, in terrestrial species, place them in damp soil.

similar to that of OLIGOCHAETES..

Largest leech - Haementeria ghilianii-  It can grow to 450 mm (17.7 in) in length and 100

mm (3.9 in) in width

Overview

“Thank You 4 Listening”

QUESTIONS

1-3. Enumerate the 3 classes of Phylum Annelida and give 1 example each.

4. Difference between protonephridia and metanephridia. 5. Function of prostomium in polychaete.6. Function of peristomium in polychaete. 7. What do you call the movement in which there is contractions of circular muscles in the anterior end lengthen the body, pushing the anterior end forward where it anchors.8. What do you call the paired appendages of polychaete that function in locomotion and breathing.9-10. What are the two transport system in class oligochaeta and give their functions.