Phylum AnnelidaSegmented Worms

Fireworm

Feather duster worm

Christmas tree worm

Leech

Annelid Characteristics• Segmentation =

Metamerism– metameres

(=somites, segments)– Show true

segmentation - both internal and external

– Allows for specialization

Annelid Systems All systems found in Annelids but skeletal

• Complete digestive tract - some specialization - crop and gizzard

• Closed circulatory system - is segmentally arranged dorsal and ventral vessels aortic arches (hearts)

• Excretion – Nephridia -

segmentally arranged

Annelid Systems All systems found in Annelids but skeletal

• Nervous system– ladder shaped– pair of cerebral

ganglia– double ventral nerve

cords– pair of ganglia in

each segment– several sensory

structures• taste buds• tactile organs• eyes in some• statocyst

Annelid Systems All systems found in Annelids but skeletal

• Reproduction– some are monoecious, others dioecious– marine species have trochophore larvae– some have asexual reproduction by

• Budding

• fragmentation

Annelid Systems

• Respiration – across body surfaces

– some have gills

– some use parapodia

Annelid Systems

Class Polychaeta

• Make up 2/3 of phylum

• most primitive annelids; ancestral to other two classes

• almost all are marine, few freshwater species

Polychaet Characteristics

• differentiated head– Tentacles

– first segment• Prostomium

• Peristomium

• Mouth– Palps

– eyes

• Parapodia- lateral appendages– notopodium-

dorsal– neuropodium-

ventral– acicula- rods

• Respiration– By parapodia

Polychaet Characteristics

• Reproduction

– sexes separate

– no permanent gonads• egg and sperm form from coelomic peritoneum

• pass out of nephridia or burst thru body wall

• fertilization is external in sea

• free swimming larva- trochophore

Polychaet Characteristics

• free living- all are predators

• tube dwelling- all are filter feeders– secrete their own tube– burrow into substrate

Polychaet Ecological Types

Class - Oligochaeta

• Terrestrial or Freshwater

• No distinct head - but contains pro- and peri- stomium

• Clitellum - present at all times– Used in copulation– Cocoon production

Class - Oligochaeta• Reproduction

– Monoecious– Copulation– Internal fertilization– Eggs laid in cocoon– no larval stage

Class - Oligochaeta

• Digestive system - well differentiated– mouth

– pharynx

– crop

– gizzard

– intestine - Typhlosole

– Anus

Class - Oligochaeta

• Circulatory system– Closed

– 5 pairs of aortic arches

– Hemoglobin

• Respiration– Body surface

• Excretion– Nephridia

Class - Hirudinea

• Freshwater or terrestrial

• Have suckers

• Segmentation fixed (34 segments)

• Clitellum only during season

• Digestive tract– large crop

– Anticoagulant

• Medically important