PHYLUM ANNELIDA.ppt

PHYLUM ANNELIDA
EMMANUEL TAIWO IDOWU Ph.D.
Department of Zoology, University of Lagos,
Akoka, Nigeria
eidowu@unilag.edu.ng

Triploblastic, bilaterally symmetrical roundworms,
Metamerically segmented (metermerism reflected in internal and
external anatomy). Only one segment being preoral
 Coelomates (coelom serves as hydrostatic skeleton)
 Specialization of the head region, with differentiated organs such
as the tentacles, palps, and eyespots.
Appendage on each segment and never jointed.
Body covered with protein cuticle, similar to arthropods cuticle.
Well developed nervous system with cephalic ganglion fused with
ventral ganglionated nerve cords, and segmental ganglia.
Closed circulatory system with several heart. Blood flow forward
dorsally and backwards ventrally. Segementally arranged
connecting vessels and a system of capillaries ensures good and
rapid blood supply
Characteristics of Annelida

Characteristics cont
 Excretory-Metanephridia or protonephridia are segmentally
arranged pairs of nephridia for removal of nitrogenous wastes and
osmotic and ionic regulation.
 Digestive system complete and extracellular. Gut is straight and end
in anus
Outer circular muscles and an inner layer of longitudinal muscles
Respiratory – reduced, dermal gas exchange through moist skin,
parapodial flaps and gills.
Larva is called trochophore
Hermaphroditic or separate sexes with asexual budding in some
species.
For removal of gametes from the gonad to the exterior,
coelomoducts grow outward through body wall from coelomic cavity.

Oligochaeta transverse section

CLASSES OF ANELLIDA
Polychaeta (Poly= many; Chaet=bristle).
 Oligochaeta (Oligo= few; Chaet=bristle).
 Hirudinea (Hirudo= leech).

Polychaeta
 Also known as sea worms or sand worms.
Possess parapodia and setae.
 Parapodia are paddle-like appendages on each
segment used in swimming that also serve as
respiratory organs.
 Setae are bristles, attached to parapodia, that
help anchor polychaetes to their substratum and
also help them move.
Distinct cephalization with complex sense organ
(distinct heads with eyes and tentacles).
 Dioecious.

Polychaeta
Based on the level of activity, morphology and ecology,
polychetes can be divided into:
Errant polychaetes
Active worms found crawling or swimming.
Well developed head bearing eyes and sensory
tentacles.
Predatory , scavengers and herbivorous.
Example Clam worms (Nereis).
Sedentary polychaetes
Sedentary and confined to tube or burrow.
Filter feeders.
Example Lugworm (Arenicola).

Phylum Annelida
Class Polychaeta

Oligochaeta
 Reduced cephalization with reduced sense organ.
They do not possess distinct head, lacks parapodia.
Head consists of a presegmental prostomium and peristomium.
Small bristles on each segment, aid in locomotion through
substrate.
Few setae protruding in clusters directly from the body.
Possess an external mucus producing bands known as clitellum.
Sexes separate or hermaphroditic.
Development is direct with no larval stage.
Important detritivores in many ecosystem.
 Free living, fresh water, terrestrial-- Earthworm

Oligochaeta
Based on habitat and feeding behaviour earthworm can
be divided into three general groups:
 Epigeic species
Live near or on the surface
Ingest large amount of undecomposed litters
Example Eisenia foetida (redworm or manure worm)
Endogenic species
Foraging below the surface
Ingest large quantities of organic rich soil and build burrows that are
horizontal in nature
Anecic species
Build permanent vertical burrows that penetrate the soil deeply.
Come to the surface to feed on partially decomposed litter manure and
other organic matter.
Example Lumbricus terrestris

Hirudinea
 Dorso-ventrally flattened. Coelom very reduced. Body wall very
muscular.
 Have fixed number of segments with many annuli.
Parapodia is absent.
Most lack setae and have suckers discs instead.
The gut is large and branched for storage of large quantities of
blood.
Clitellum is present.
Hermaphroditic.
Free-living predators/ ectoparasitic.
 Example: Tropical blood sucking leech- Haemadipsa
Giant Amazonia leech- Haementeria ghilianii
Medicinal leech- Hirudo medicinalis

Digestive Systems
Polychaeta
Digestive systems is divided into a pharynx, oesophagus, intestine and rectum.
Oligochaeta
The esophagus may be modified to form a crop for food storage, and or gizzard.
 Calciferous glands are associated with oesophagus.
Terrestrial oligochaete species are thrown into ridges or folds (typhlosole).
Associated with the intestine (dorsal blood vessel) of oligochaetes is characteristic
yellow tissue called chloragogen.
Hirudinea
The mouth of a leech opens to muscular pumping pharynx.
Salivary glands associated the pharynx secret hirudin, an anticoagulant.
A crop and digestive glands is found in some species.

Hirudotheraphy
 Local anesthetics.
Anticoagulant enzymes—hirudin.
Vasodilator and prostaglandin.

Phylum Annelida
Class Hirundinea

PHYLUM ANNELIDA.ppt

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