EarthWorms

Why do more complex animals require a coelom?

To provide space for specialized organs and organ systems.

What is a coelom?

A muscle-lined body cavity containing organs and body systems.

What functions can occur because of a coelom?

Circulation, respiration, digestion, excretion, and movement.

What are body segments?

Repeating anatomical sections of the body.

What are the three classes of annelids?

Oligochaeta, Polychaeta, and Hirudinea.

What organisms belong to Class Oligochaeta?

Earthworms (e.g., Genus Lumbricus).

What organisms belong to Class Polychaeta?

Tubeworms (e.g., Nereis).

What organisms belong to Class Hirudinea?

Leeches.

What is the cuticle?

The segmented outer covering of annelids.

How does respiration occur in earthworms?

: By diffusion through the cuticle.

Why must the earthworm cuticle stay moist?

To prevent dehydration and allow gas exchange.

What secretes mucus in earthworms?

The cuticle.

What is the clitellum?

A thickened section of the cuticle involved in reproduction.

Where is the clitellum located?

About 1/5 of the way from the anterior end.

What does the clitellum secrete?

Slime during reproduction.

What is the prostomium?

The dorsal lip at the anterior end.

What are setae?

Bristles on the ventral surface used for movement and grip.

What is the defining characteristic of Oligochaeta?

Few bristles (setae) per segment.

What does “oligo” mean?

Few.

What does “chaeta” mean?

Bristles or teeth.

How many pairs of setae does an oligochaete have per segment?

Two pairs

What divides the coelom into segments?

Septa.

What are septa?

Internal walls separating body segments.

Which organ systems are specialized in annelids?

Digestive, circulatory, nervous, excretory, and reproductive systems.

Why are annelids more complex than flatworms?

They have a true coelom and specialized organ systems.

What is the function of mucus on the cuticle?

Prevents drying out and helps respiration.

What structure is unique to earthworms during reproduction?

The clitellum.

What structure helps earthworms grip the soil?

Setae.

Why is the coelom important for earthworm movement?

It allows body wall muscles and digestive muscles to function independently.

What muscle types line the intestine and cuticle

Circular muscles and longitudinal muscles.

What happens when circular muscles contract?

The body becomes constricted and longer.

What happens when longitudinal muscles contract?

The body shortens.

Why is this muscle arrangement advantageous?

It allows movement without stopping digestion.

What is the function of the pharynx in earthworms?

Swallowing detritus (soil with organic matter).

What is detritus?

Soil containing organic material.

What moves food through the esophagus?

Peristalsis.

What is peristalsis?

Rhythmic muscular contractions that move food.

What is the function of the crop?

Storage of food.

What is the function of the gizzard?

Grinding food mechanically.

How does the gizzard grind food?

With strong muscles and a rough interior.

Where are digestive enzymes secreted in earthworms?

From digestive glands on the dorsal side of the intestine.

Where are nutrients absorbed in earthworms?

Throughout the intestine.

: What are castings?

Waste material excreted from the anus.

What are the two major blood vessels in earthworms?

Dorsal and ventral blood vessels.

Which direction does blood move in the dorsal vessel?

: Anteriorly.

Which direction does blood move in the ventral vessel?

Posteriorly.

What connects the dorsal and ventral blood vessels?

Segmental vessels.

What are aortic arches?

Muscular blood vessels acting as hearts.

How many pairs of aortic arches do earthworms have

Five pairs.

What is the function of aortic arches?

Maintain blood circulation.

What type of nervous system do earthworms have?

Paired ventral nerve cords.

How is the earthworm nervous system similar to planaria?

Both have ventral nerve cords.

What forms the earthworm brain?

The ventral nerve cords separating and surrounding the digestive tube.

Describe the earthworm brain

Small, dorsal, and bi-lobed.

What are nephridia?

Excretory organs in earthworms.

What do nephridia do?

Collect and remove liquid wastes.

How are wastes removed from the body?

Through tubes ending at pores in the cuticle.

Are earthworms hermaphroditic?

Yes.

What reproductive organs do earthworms possess?

Testes, ovaries, sperm receptacles, and yolk sacs.

How do earthworms mate?

Two worms align in opposite directions with ventral surfaces together.

What is the function of slime from the clitellum?

Encases reproductive regions during mating.

Where is sperm stored after mating?

In sperm receptacles

Where does fertilization occur in earthworms?

Outside the worm in a slime covering.

What type of larvae do earthworms produce?

Trochophore larvae.

Describe trochophore larvae.

Microscopic spherical larvae with cilia.

How do earthworms improve soil quality?

By aerating soil and increasing water penetration.

How do earthworms help plant growth?

Increased soil aeration helps nitrifying bacteria produce nitrates.

What economic and recreational use do earthworms have?

Fish bait.

Difference between crop and gizzard?

Crop stores food; gizzard grinds food.

Function of circular vs longitudinal muscles?

: Circular = construction longitudinal = shortening.

Function of aortic arches?

Maintain blood circulation

Function of nephridia?

Excretion of liquid wastes.

Why are earthworms important ecologically?

Soil aeration and nutrient cycling.