ACAD Phylum Annelida
Copyright Pearson Prentice Hall What Is an Annelid? Annelids are worms with segmented bodies. They are coelomates with a true coelom that is lined with mesoderm tissue. They have bilateral symmetry.
Copyright Pearson Prentice Hall Body Plan and Structure The body of an annelid is divided into segments. Each segment is separated by septum, which are internal walls between each segment.
Copyright Pearson Prentice Hall Three Germ Layers of an Annelid
Copyright Pearson Prentice Hall Body segments may carry “eyes”, antennae, other sense organs, or be specialized for functions such as respiration. Setae - bristles attached to each segment, used to grasp/hook onto the ground to help crawl Annelids have a one-way digestive tract where food passes through from the mouth to the anus.
Copyright Pearson Prentice Hall Feeding and Digestion In carnivorous species, the pharynx usually holds two or more sharp jaws that are used to attack prey (Leeches) Annelids that feed on decaying vegetation have a pharynx covered with sticky mucus (Earthworms)
Copyright Pearson Prentice Hall In earthworms, the pharynx pumps food and soil into the esophagus. The food then moves through the crop, where it can be stored. It then moves through the gizzard, where it is ground into smaller pieces before going through the intestine
Copyright Pearson Prentice Hall Form and Function in Annelids Annelids have complex organ systems. Many of these systems are unique because of the segmented body plan of this group.
Copyright Pearson Prentice Hall Circulation Annelids typically have a closed circulatory system, in which blood is contained within a network of blood vessels. Aortic arches – five pairs of muscular tubes that act as a heart and pump blood
Copyright Pearson Prentice Hall Respiration Aquatic annelids often breathe through gills. Land-dwelling annelids take in oxygen and give off carbon dioxide through their moist skin via diffusion
Copyright Pearson Prentice Hall Excretion Nephridia are excretory organs that filter fluid in the coelom to clean out nitrogen wastes Nephridia
Copyright Pearson Prentice Hall Neural Control/Response Most annelids have a well-developed nervous system consisting of a brain and several nerve cords. Ganglia Brain
Copyright Pearson Prentice Hall Body Support/Movement Annelids have two groups of body muscles that function as part of a hydrostatic skeleton (water- filled for support) Longitudinal muscles Circular muscles
Copyright Pearson Prentice Hall Reproduction Most annelids reproduce sexually. Earthworms are hermaphrodites. Two worms attach to each other, exchange sperm, and then store the sperm in special sacs.
Copyright Pearson Prentice Hall A clitellum is a band of thickened, specialized segments. After eggs are fertilized in the ring, the ring slips off the worm's body and forms a protective cocoon. Young worms hatch weeks later.
Copyright Pearson Prentice Hall Groups of Annelids Annelids are divided into three classes: oligochaetes hirudinea polychaetes
Copyright Pearson Prentice Hall Oligochaetes Oligochaetes contains earthworms and their relatives. Typically have streamlined bodies. Most oligochaetes live in soil or fresh water.
Copyright Pearson Prentice Hall Hirudinea The class Hirudinea contains the leeches. Leeches are typically external parasites that suck the blood and body fluids of their host.
Copyright Pearson Prentice Hall Polychaetes Polychaetes are marine annelids that have paired, paddlelike appendages tipped with setae. The setae are brushlike structures on the worm.