ANNELIDS ANNELIDS WHAT IS AN ANNELID What Is

ANNELIDS

ANNELIDS

WHAT IS AN ANNELID? • What Is an Annelid? • Annelids are worms with segmented bodies. They have a true coelom that is lined with tissue derived from mesoderm. Copyright Pearson Prentice Hall

WHAT IS AN ANNELID? • Three Germ Layers of an Annelid

WHAT IS AN ANNELID? • 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

WHAT IS AN ANNELID? • Body segments may carry eyes, antennae, other sense organs, or be specialized for functions such as respiration. • Bristles called setae may be attached to each segment. • Annelids have a tube-within-a-tube digestive tract that food passes through from the mouth to the anus. Copyright Pearson Prentice Hall

FORM AND FUNCTION IN ANNELIDS • 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

DIGESTION • 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

DIGESTION • In earthworms, the pharynx pumps food and soil from the mouth 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. • Finally into the intestine for nutrients to be absorbed

CIRCULATION! • Annelids typically have a closed circulatory system, in which blood is contained within a network of blood vessels. • Dorsal Vessel • Blood moves towards head • Ventral Vessel • Blood moves away from head • 5 Pumping organs (aortic arches) • Acts like your heart, to pump blood around worm

RESPIRATION • Aquatic annelids often breathe through gills. • An organ specialized for exchange of gases underwater. • Land-dwelling annelids take in oxygen and give off carbon dioxide through their moist skin. Diffusion • These animals secrete mucus to keep skin moist, for better diffusion!

EXCRETION • Digestive wastes pass through anus • Cellular wastes (nitrogen) is eliminated by nephridia • Nephridia are excretory organs that filter fluid in the coelom. Nephridia

NERVOUS SYSTEM • Most annelids have a well-developed nervous system consisting of a brain and several nerve cords. • Aquatic annelids have best developed sense organs • Sensory tentacles, chemical receptors, eyes, and statocysts (gravity) Brain Ganglia Nerve collar

MOVEMENT • Annelids have two groups of body muscles that function as part of a hydrostatic skeleton. • Longitudinal muscles • Run from anterior to posterior • Contact to make the worn short and fat • Circular muscles • Wrap around body • Contract to make the worm long and skinny • Setae are used to keep worm in place while contracting muscles

REPRODUCTION • Most annelids reproduce sexually. • Earthworms are hermaphrodites. Two worms attach to each other, exchange sperm, and then store the sperm in special sacs.

REPRODUCTION • A clitellum is a band of thickened, specialized segments that secrete mucus when eggs are ready. • Eggs and sperm are released here, and fertilized • Generally not self fertilized • 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.

REPRODUCTION • Asexual Reproduction • Sometimes seen in Oligochaetes and Polychaetes • Oligochaetes will sometimes regrow from segments of their body • Polychaetes will often use budding as a form of reproduction

GROUPS OF ANNELIDS • Annelids are divided into three classes • Oligochaetes • Leeches • Polychaetes

GROUPS OF ANNELIDS • Oligochaetes contains earthworms and their relatives. • Oligochaetes typically have streamlined bodies and relatively few setae compared to polychaetes. Most oligochaetes live in soil or fresh water.

GROUPS OF ANNELIDS • Leeches • The class Hirudinea contains the leeches. • Leeches are typically external parasites that suck the blood and body fluids of their host. • https: //www. youtube. com/watch? v=5 IVmwg 59 MXY Copyright Pearson Prentice Hall

GROUPS OF ANNELIDS • Polychaetes are marine annelids that have paired, paddlelike appendages tipped with setae. • The setae are brushlike structures on the worm.

ECOLOGY OF ANNELIDS • Earthworms • Aerate soil, so roots get oxygen (2 m) • Tunnels provide passageways for roots • Bring plant matter down into soil • Eat it, digest it, and mix it with bacteria • Feces rich in nitrogen and micronutrients • Important in diets of birds, moles, toads, snakes. • Marine • Larvea are part of the plankton group • Food chains • “stir up” marine sediment