Prepared by : Nada H. Lubbad Phylum Annelida Prepared by : Nada H. Lubbad

Characteristics Eucoelomates (true coelomate). Metamerism ( Repeating segmentation). Cephalization (well developed nervous system). Triploblastic. Bilateral symmetry. Terrestrial, marine, freshwater.

Systems 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.

Hydrostatic Skeleton

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. 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.

Reproductive System ,most annelids are hermaphroditic, but they are usually cross fertilizers. Earthworms and leeches form pairs and reciprocally fertilize one another. Some annelids (e.g. marine sandworms) are dioecious and they release eggs and sperm into the marine environment, where gametes unite to form trochophore larvae. Trochophore

Class Polychaeta (many bristles) most numerous species Marine free swimming Live in temporary burrows in sand Sex separate External fertilization , zygote , larva , adult . Nereis

Parapodia function in: The body wall is extended laterally into a series of thin, flattened outgrowths called parapodia Parapodia function in: Gas exchange between the worm and its environment. Locomotory function in many species due to the presence of chitinous support rods called acicula. In addition, siliceous, chitinous, or, more rarely, calcareous bristles called setae protrude from each parapodium. Parapodium of Nereis

Polychaete Anatomy (cross section)

Class Oligochaeta (few bristles) earthworms Live in damp soil. Nocturnal. Hermaphrodite. Body cylindrical. Anterior (pointed) Posterior (dors –ventrally flattened ) No parapodia and reduced number of setae. Reduced prostomium and peristomium. Lumbricus terrestris Clitelium functions in reproduction (secretes the cocoon ) is thickened skin of segments 26-34.

Oligochaete Anatomy

Oligochaete Anatomy

Oligochaete Reproduction

Class Hirudinea Fixed segments (34) Setae and parapodia are absent Shortened body. The body is generally not separated into compartments by septa, and the continuous coelomic space is largely filled with connective tissue, or mesenchyme Have two suckers, Leeches locomote over solid substrates by using suckers as temporary anchores. Lives in ponds , marshes and streams. Feeds on vertebrates blood. Ectoparasites.

An application of Hirudo medicinalis, the medical leech, help in 2 ways: Drains off the excess blood from the finger. Injects an anticoagulant-hirudin- مادة مضادة للتجلطthat keeps the blood flowing out from the bite-wound long after the sated leech has dropped off.

Class Hirudinea