Phylum Annelida

Segmented Worms

Metameres in Polychaeta

metamere = segment, or repeating body unit

Metameric Organs and Systems

– Coelom– Nerves and ganglia– Metanephridia

• paired excretory and osmoregulatory organs

– Blood capillaries• of the closed circulatory system

– Parapodia

Classification of Annelida

• c. Polychaeta bristle worms• c. Clitellata

– sc. Oligochaeta earthworms– sc. Hirudinea leeches

Class Polychaeta

“many chaetae”– also called setae

• complex head appendages and parapodia – fit them for many feeding niches

• important members of marine benthos– deposit-feeders, filter-feeders, carnivores

Polychaete AnatomyHickman Fig. 10-2

parapods

prostomium

(jaws protruding)

Polychaete DiversityHickman Fig. 10-3A, 10-4, 10-10

paper tube worm(filter-feeder)

lug worm(deposit-feeder) sand worm

(carnivore)

surface deposit-feeder

Trochophore Larva

• Present in many marine Polychaeta– same as Mollusca and other phyla

• [Clitellata have direct development]. . . egg to juvenile with no larva

Oligochaeta - “few chaetae”a subclass of Clitellata

• many terrestrial and freshwater but few marine species– mostly thread-sized– mostly deposit-feeders

• which mainly digest bacteria• a few are grazers or carnivores

• freshwater species composition indicates water quality

Earthworm Anatomy Campbell Fig

33.23

Hermaphroditic OligochaeteHickman Fig. 10-11 A

Monecious

• guides sperm transfer in mating

• forms cocoon for eggs

Clitellum Functioncompare Hickman Fig. 10-15

Metamere features

Hirudineaanother subclass of Clitellata

• anterior and posterior suckers• expandable intestinal caeca• no chaetae or internal septa• hermaphrodites• clitellum visible only during egg-laying

Leech AnatomyHickman Fig. 10-18B

Leech Biology

• nearly all freshwater• many are carnivores, not parasites• produce anesthetics, anti-clotting enzymes,

and antiseptics • larger blood-suckers have medical uses

– relieve excessive swelling and blood pressure near tissue grafts