Phylum Annelida

Learning Outcomes

Students should be able to:

• Describe the unifying characteristics of members of phylum annelidamembers of phylum annelida

• Describe how annelids carry out their life functions

• Describe the ecological roles of annelids

Phylum Annelida

Leeches

General Information

• Annelids are ringed, segmented worms

• Examples include earthworms and leeches

• Habitat: terrestrial, fresh water, marine• Habitat: terrestrial, fresh water, marine

• Have bilateral symmetry with 3 body layers (ectoderm, mesoderm, & endoderm)

3 Unique Features

• Have a true coelom (body cavity) lined by mesoderm

• Have externally visible body segmentation• Have externally visible body segmentation

• Have a closed circulatory system

Coelom

• Located between the body wall and the intestine

• Lined by mesoderm

• Filled with fluid• Filled with fluid

• Acts as a buffer between body muscles and the intestine (allows worm to move without putting pressure on the intestine)

Body Segmentation

• The body is divided into segments

• Each segment contains a portion of the coelomic cavity

Class Polychaeta

• Polychaete worms

• Marine

• Flattened bodies

• Body segments with • Body segments with

paired paddle-like

appendages

(parapodia)

Class Oligochaeta

• Earthworms

• Have a few hairs

• Small head for burrowing

• May have a saddle-like swelling (clitellum)• May have a saddle-like swelling (clitellum)

Class Hirudinea

• Leeches

• Often aquatic

• Bodies with suckers

• Many are • Many are

ectoparasites feeding

on blood

Earthworm Ingestion

• Earthworms have a complete digestive system (one way digestive tract)

• Food (organic material in the soil) enters through the mouththrough the mouth

• The pharynx draws food into the mouth (suck in and swallows food)

• Food moves through the esophagus to the crop where it is stored temporarily

Earthworm Digestion

• Food moves from the crop to the gizzard

• Gizzard contains sand grains which help grind up food by muscular contractions

• Food moves into the intestine where • Food moves into the intestine where enzymes chemically digest (break down) food into particles small enough to be absorbed into blood

• Intestine has a typhlosole which increases the surface area for nutrient absorption

Earthworm Elimination

• Undigested food waste moves to the end of the intestine and exits through the anus

Earthworm Respiration

• Gas exchange (O2 & CO2) happens via diffusion through the moist skin

• Mucus glands secrete mucus to keep skin moistmoist

• O2 diffuses across the moist skin and into the capillaries and blood

• O2 is carried by hemoglobin (Hb) in the blood

Earthworm Circulation

• Earthworms have a closed circulatory system (blood is always contained in vessels)

• Closed circulatory systems allow for more • Closed circulatory systems allow for more effective delivery of nutrients which allows for increased activity and size

• Earthworms have 5 pairs of hearts which pump blood through the vessels

Earthworm Excretion

• Excretory organs called nephridia filter excess H2O and nitrogenous wastes from the coelomic cavity of one segment

• This waste passes through a long tube surrounded by blood vessels (much like surrounded by blood vessels (much like our kidneys) and eventually exits through an excretory pore in the next segment

• Excess water is reabsorbed into the blood vessels

Earthworm Sexual Reproduction

• Earthworms are hermaphrodites (male & female on same individual)

• 2 earthworms cross-fertilize (exchange sperm)sperm)

• Earthworms have a swelling called a clitellum which secretes a mucus cocoon into which fertilized eggs are deposited

Earthworm Asexual Reproduction

• Earthworms are able to regenerate missing body parts

Earthworm Nervous System

• Earthworms have a paired ventral nerve cord which swells into ganglia (a mass of nerve cell bodies acting as a primitive brain) at the headbrain) at the head

Earthworm Locomotion• Uses longitudinal and circular muscles

combined with the fluid pressure in the coelom and the setae (bristles) to help burrow and move

• Contraction of the circular muscles of • Contraction of the circular muscles of anterior (front) cause worm to lengthen

• Paired setae (bristles) anchor worm to soil

• Longitudinal muscles contract causing worm to shorten pulling it’s posterior (tail end forward)