Oligochaeta Class Flashcards

Study Notes

Overview of Oligochaeta

Oligochaeta means "few bristles," referring to the limited number of setae (bristles) present on their bodies.
They primarily inhabit soil and freshwater environments.

Structural Characteristics

Oligochaetes lack parapodia, which are paired appendages found in other worm classes.
The body is segmented, comprising over 100 identical segments that facilitate locomotion.
Body muscles include circular and longitudinal muscles along the interior, aiding in movement by contracting and anchoring segments.

Locomotion

Earthworms use setae to anchor segments to the ground while contracting their muscles to extend their bodies.
This process increases coelomic pressure, elongating the worm and advancing the anterior end.
The contraction of longitudinal muscles and gripping of the anterior segment propel the posterior segments forward.

Feeding and Digestion

Earthworms ingest soil through their pharynx, with food passing down the esophagus to the crop for storage.
The gizzard processes the soil by grinding it and releasing nutrients.
The intestines, featuring an infolding called the typhlosole, enhance absorption of digested compounds, with undigested waste expelled through the anus.

Circulatory System

They possess a closed circulatory system for circulating oxygen, carbon dioxide, nutrients, and waste.
Blood flows posteriorly through the ventral blood vessel, returning anteriorly via the dorsal blood vessel.
Aortic arches link the two vessels, facilitating blood circulation through contractions of the vessels.

Respiratory System

Earthworms lack specialized respiratory organs; respiration occurs through the skin, where gases diffuse directly.
Moist skin is essential for respiration, maintained by mucus secretions and avoidance of dry conditions.

Excretory System

Excretion is managed by nephridia, functioning like kidneys to eliminate cellular wastes and excess water.
Each segment (excluding the first three and the last) contains a nephridium that allows reabsorption of nutrients into the blood before expelling waste through pores.

Reproductive System

Earthworms are hermaphrodites but cannot self-fertilize; mating involves two worms aligning and exchanging sperm.
After mating, the clitellum secretes a mucous tube for fertilization, where eggs and sperm meet.
Young develop within this protective casing for about 2-3 weeks prior to hatching.

Neural Control

The nervous system consists of a chain of ganglia connected by a nerve cord, managing muscle impulses and sensory responses.
Anterior segments contain fused ganglia, known as cerebral ganglia or a brain, enabling information processing from various sensory structures.

Description

Explore the essential characteristics of Oligochaeta with these flashcards. Discover where they live, their physical traits, and understand examples like the earthworm. Perfect for quick review and reinforcement of key concepts!