End Show Slide 1 of 36 Copyright Pearson Prentice Hall Biology

End Show Slide 2 of 36 Copyright Pearson Prentice Hall 27-3 Annelids

End Show 27-3 Annelids Slide 3 of 36 Copyright Pearson Prentice Hall What Is an Annelid? Annelids are worms with segmented bodies. They have a true coelom that is lined with tissue derived from mesoderm.

End Show 27-3 Annelids Slide 4 of 36 Copyright Pearson Prentice Hall 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.

End Show 27-3 Annelids Slide 5 of 36 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.

End Show 27-3 Annelids Slide 6 of 36 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.

End Show 27-3 Annelids Slide 7 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Feeding and Digestion In carnivorous species, the pharynx usually holds two or more sharp jaws that are used to attack prey. Annelids that feed on decaying vegetation have a pharynx covered with sticky mucus. Other annelids obtain nutrients by filter feeding.

End Show 27-3 Annelids Slide 8 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids 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. The food is absorbed farther along in the digestive tract in the intestine.

End Show 27-3 Annelids Slide 9 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Circulation Annelids typically have a closed circulatory system, in which blood is contained within a network of blood vessels.

End Show 27-3 Annelids Slide 10 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Blood in the dorsal (top) vessel moves toward the head of the worm. The dorsal blood vessel functions like a heart because it contracts rhythmically and helps pump blood. Dorsal blood vessel

End Show 27-3 Annelids Slide 11 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Blood in the ventral (bottom) vessel runs from head to tail. Ventral blood vessel

End Show 27-3 Annelids Slide 12 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids In each body segment, a pair of smaller blood vessels connect the dorsal and ventral blood vessels and supply blood to the internal organs.

End Show 27-3 Annelids Slide 13 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Respiration Aquatic annelids often breathe through gills. A gill is an organ specialized for the exchange of gases underwater. Land-dwelling annelids take in oxygen and give off carbon dioxide through their moist skin.

End Show 27-3 Annelids Slide 14 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Excretion Digestive waste passes out through the anus. Cellular waste containing nitrogen is eliminated by nephridia.

End Show 27-3 Annelids Slide 15 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Nephridia are excretory organs that filter fluid in the coelom. Nephridia

End Show 27-3 Annelids Slide 16 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Response Most annelids have a well-developed nervous system consisting of a brain and several nerve cords. Ganglia Brain

End Show 27-3 Annelids Slide 17 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Movement Annelids have two groups of body muscles that function as part of a hydrostatic skeleton. Longitudinal muscles run from the front of the worm to the rear and can contract to make the worm shorter and fatter.

End Show 27-3 Annelids Slide 18 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Circular muscles wrap around each body segment and can contract to make the worm longer and thinner. The earthworm moves by alternately contracting these two sets of muscles.

End Show 27-3 Annelids Slide 19 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids Reproduction Most annelids reproduce sexually. Some species use external fertilization and have separate sexes. Other annelids are hermaphrodites. Two worms attach to each other, exchange sperm, and then store the sperm in special sacs.

End Show 27-3 Annelids Slide 20 of 36 Copyright Pearson Prentice Hall Form and Function in Annelids When eggs are ready for fertilization, a clitellum secretes a mucus ring into which eggs and sperm are released. 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.

End Show 27-3 Annelids Slide 21 of 36 Copyright Pearson Prentice Hall Groups of Annelids What are the characteristics of the three classes of annelids?

End Show 27-3 Annelids Slide 22 of 36 Copyright Pearson Prentice Hall Groups of Annelids Annelids are divided into three classes Oligochaetes (earth worms) Hirudineans (leeches) Polychaetes (sandworms, bloodworms…)

End Show 27-3 Annelids Slide 23 of 36 Copyright Pearson Prentice Hall Groups of Annelids Oligochaetes 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.

End Show 27-3 Annelids Slide 24 of 36 Copyright Pearson Prentice Hall

End Show 27-3 Annelids Slide 25 of 36 Copyright Pearson Prentice Hall 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.

End Show 27-3 Annelids Slide 26 of 36 Copyright Pearson Prentice Hall Groups of Annelids Leeches have powerful suckers at both ends of their bodies that help them cling to their hosts. Some leeches force a muscular extension called a proboscis into the tissue of their host. Others slice into the skin with a razor-sharp pair of jaws.

End Show 27-3 Annelids Slide 27 of 36 Copyright Pearson Prentice Hall Groups of Annelids The leech uses its pharynx to suck blood from the wound. Some leeches release a substance that anesthetizes the wound—keeping the host from knowing it has been bitten. Leeches were once used to treat medical conditions.

End Show 27-3 Annelids Slide 28 of 36 Copyright Pearson Prentice Hall Leech

End Show 27-3 Annelids Slide 29 of 36 Copyright Pearson Prentice Hall Groups of Annelids Polychaetes Polychaetes include sandworms, bloodworms, and their relatives. Polychaetes are marine annelids that have paired, paddlelike appendages tipped with setae that they use for locomotion, called parapodia. The setae are brushlike structures on the worm.

End Show 27-3 Annelids Slide 30 of 36 Copyright Pearson Prentice Hall Polychaeta Although many of the smaller polychaetes lack respiratory structures, the larger one do possess gills. Gills are usually modifications of the parapodia. Although a number of polychaetes are active predators, some are sedentary and burrow into mud or live in protective tubes in the mud In several of these species filter feeding has evolved

End Show 27-3 Annelids Slide 31 of 36 Copyright Pearson Prentice Hall Polychaeta Polichaetes live in different ways: Burrows in mud or sand. Under rocks or coral In permanent tubes.

End Show 27-3 Annelids Slide 32 of 36 Copyright Pearson Prentice Hall

End Show 27-3 Annelids Slide 33 of 36 Copyright Pearson Prentice Hall Ecology of Annelids Earthworms and many other annelids spend their lives burrowing through soil, aerating and mixing it. Earthworms help plant matter decompose. Earthworm castings are rich in nitrogen, phosphorus, potassium, micronutrients, and beneficial bacteria. Ecology of Annelids

End Show - or - Continue to: Click to Launch: Slide 34 of 36 Copyright Pearson Prentice Hall 27-3

End Show Slide 35 of 36 Copyright Pearson Prentice Hall 27-3 In the earthworm, food is absorbed in an organ called the a.intestine. b.crop. c.gizzard. d.clitellum.

End Show Slide 36 of 36 Copyright Pearson Prentice Hall 27-3 Annelids differ from other worm phyla because they have a.segmented bodies and a true coelom. b.unsegmented bodies and a pseudocoelom. c.mesoderm and one opening in the digestive system. d.segmented bodies and one opening in the digestive system.

End Show Slide 37 of 36 Copyright Pearson Prentice Hall 27-3 How many major blood vessels does an earthworm have? a.one b.two c.three d.none

End Show Slide 38 of 36 Copyright Pearson Prentice Hall 27-3 Ecologically, one of the most beneficial functions of an earthworm is to a.provide food for tropical fish. b.suck the blood of dead animals. c.aerate the soil. d.kill pest insects that inhabit the soil.

End Show Slide 39 of 36 Copyright Pearson Prentice Hall 27-3 In an earthworm, the thickened bank of specialized segments is the a.nephridia. b.gizzard. c.clitellum. d.seta.

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