Annelida General Characteristics, Classification and Examples

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Annelida General Characteristics

Habit & habitat :- Terrestrial, fresh water or marine. Free living or parasitic
Lamarck coined the term annelida for ringed animals
Body is soft elongated, cylindrical and divided into segments or metameres
Body wall consist of Cuticle = Moist and elastic, Epidermis – Living layer that secretes cuticle, Muscle layer – Contains circular and longitudinal muscles
Anterior end has a distinct head with sense organ
Body cavity is true coelom lined by mesodermal epithelium
Digestive system is complete, straight and extends through entire body
Respiration is through moist skin, some have gills
Circulatory system is closed type and pulsatile heart present
Excretory organ is nephridia
Nervous system consist of nerve ring and double ventral nerve cord
All annelids except leeches also have chitinous hairlike structures, called setae
Classification of annelida is based on position & arrangement of setae
Reproduction is sexual
Annelids may be monoecious or dioecious
Clitellum present in bisexual annelids is useful in the formation of cocoon
They are oviparous and the eggs are laid in ootheca or cocoons or egg case
Development is direct or indirect with free swimming ciliated trochophore larva
Mostly cross fertilization takes place