Phylum Annelida Overview

Phylum Annelida

• Commonly known as segmented worms
• 15,000 species
• Worldwide distribution
• Soft bodies
• Sizes range from less than 1mm to many meters
• Include marine worms, freshwater worms, terrestrial worms, and leeches

Annelida Characteristics

• Bilaterally symmetrical and triploblastic
• Segmented body composed of metameres (metamerically segmented)
• Eucoelomate
• Coelom lined by mesoderm
• Coelom filled with fluid, acting as a buffer for movement

Annelida Body Wall

• Integument: single cell layer epidermis with mucous glands secreting a moist cuticle (protective layer)
• Muscles: outer circular and inner longitudinal muscle layers, each segment's muscles are independent of the other segments
• Respiration: occurs through skin, parapodia, or gills

Annelida Circulation

• Closed circulatory system
• Blood vessels run length of body and branch into each segment
• Blood contains hemoglobin, increasing oxygen transport ability
• Includes a pharynx, stomach, intestine, and accessory glands

Annelida Nervous System

• Well-developed nervous system
• Ventral nerve cord
• Ganglia (masses of nerve cells) at the head (primitive brain)
• Segmental nerves branch from ganglia

Annelida Excretion

• Excretion through nephridia
• One pair per metamere (segment)
• Similar to kidneys, filtering excess water and nitrogenous wastes

Annelida Reproduction

• Hermaphroditic (both male and female reproductive organs)
• Fertilization is external
• Cocoons are formed by the clitellum
• Some species have a free-swimming trochophore larva

Class Oligochaeta

• Primarily freshwater and terrestrial
• Lack parapodia
• Have few, short setae (bristles)
• Have a clitellum (saddle-like swelling)
• Examples: earthworms

Class Polychaeta

• Primarily marine
• Have parapodia (paddle-like appendages) with chaetae (bristles)
• Well-developed head
• Examples: sand worms, clam worms

Class Hirudinea (Leeches)

• Primarily freshwater, some marine or terrestrial
• Lack parapodia and setae
• Possess suckers for attachment
• Mostly fluid feeders (bloodsuckers, carnivores on small invertebrates)
• Clitellum apparent only during reproduction
• Examples: medicinal leech

Medical Importance

• Leech saliva contains antiseptic chemicals and hirudin (anticoagulant)
• Used in reconstructive surgery to promote blood circulation

Explore the fascinating world of Phylum Annelida, commonly known as segmented worms. This quiz covers their characteristics, body structure, and circulation system, highlighting their unique adaptations and worldwide distribution. Test your knowledge on the diverse types of annelids and their importance in the ecosystem.