Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.5: Annelids are segmented worms The phylum Annelida is made up of segmented worms, numbering about 15,000 species. Body segmentation, which first appears in the fossil record in annelids, was a major step in the evolution of animals. The name annelida comes from the latin “annelus” meaning little rings. Each segement is called an annulus.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.5: Annelids are segmented worms Annelids are protosomes, meaning they have a coelom made from cell masses. This coelom is divided into a series of repeated parts. This repetition is called metamerism, and each segment is called a metamere.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.5: Annelids are segmented worms There are a cluster of nerve cells and excretory organs in each metamere, but the ventral nerve cords, a dorsal and ventral blood vessel, and the digestive tract pass through the walls of segmentation and are therefore unsegmented.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.5: Annelids are segmented worms These walls, or septum, are thin sheets of mesodermic tissue, isolating the coelom. Except for the head and tail region, each with an opening of the digestive tract, making it a complete tract, each segment in an annelid is ringlike and very similar.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Segmentation allows for flexibility and mobility because annelids can bend at segmented parts. Therefore, because a segmented body is advantageous, it evolved twice, with the protosomes, as shown by phyla Annelida and Arthropoda, and again in the deuterosomes, as shown by phylum Chordata. Concept 33.5: Annelids are segmented worms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other hallmarks of the annelids are soft bodies that are round in cross section, repetition of organs in the segemented parts, and a body that is much longer than it is wide. There are three main classes in the phylum Annelida. Concept 33.5: Annelids are segmented worms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Classes of Annelids The phylum Annelida is divided into three classes Table 33.4

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Annelids with a clitellum (a swelling towards the head of the animal, where the gonads are located) are classified in the superclass Clitellata, which is further divided into classes Hirudinea (leeches) and Oligochaeta (including the earthworms). The Polychaeta lack a clitellum and have parapodia, paddle-like appendages with numerous bristles or chaetae. Classes of Annelids

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Of the approximately 9000 species of annelids, more than 8000 are polychaetes. These segmented worms are among the most common marine organisms, and can be found living in the depths of the ocean, floating free near the surface, or burrowing in the mud and sand of the beach. Some, such as Eunice gigantea, may reach three meters long. Classes of Annelids

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Polychaetes are known by many names: lugworms, clam worms, bristleworms, fire worms, palolo worms, sea mice, featherduster worms, etc., but all possess an array of bristles on their many leg-like parapodia -- the name polychaete, in fact, means "many bristles". The many common names reflect the wide array of body forms found in this group, unlike the earthworms and leeches which all have the same general appearance. Classes of Annelids

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Class Polychaeta consists of mostly marine annelids. Polychaetes are the largest group of annelids, and have hard bristles that allow the worms to wriggle and move. However, only one type of polychaetes actually move. Polychaetes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many polychaetes live in tubes that they make from sticky proteins secreted near the mouth. Feathery appendages extending from the tubes trap food in the water. An example of a tube-building polychaete is a Christmas tree worm. Polychaetes usually have at least one set of eyes, one set of sensory organs, and are either male or female. Polychaetes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Polychaetes Members of class Polychaeta – Possess paddlelike parapodia that function as gills and aid in locomotion Parapodia

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Resembling giant lipsticks, tubeworms (Riftia pachyptila) live over a mile deep on the Pacific Ocean floor near hydrothermal vents. They may grow to about 3 meters (8 ft) long. The worms’ white tube home is made of a tough, natural material called chitin (pronounced “kite-in”). Polychaetes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Class Oligochaeta consist of earthworms and other worms that live in terrestrial or freshwater environments. As shown by the class name (meaning few setae, or appendages), these worms lack the bristles that allow movement and increase surface area. There are some that are marine, but most (94%) live out of sea water. Oligochaetes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings All oligochaetes are hermaphroditic, neither male nor female. One oligochaete, the earthworm, extracts nutrients from the soil as it burrows, excreted from the anus. Because the nutrients that earthworms dig up are necessary for fertile soil, these earthworms are an intricate part of farms, actually tilling the soil. Oligochaetes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The largest earthworm ever found was in South Africa and was 22 feet long! Oligochaetes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The final major class in phylum Annelida, class Hirudinea, consists of the leeches. Leeches are known for sucking the blood of humans, but most are free-living and eat small invertebrates, feeding on their blood. Hirudinea

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Like earthworms, leeches are hermaphroditic and lack appendages. To successfully drink the blood, they have a small sucker in the anterior end and a larger one in the posterior end. Hirudinea

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hirudinea

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings During the reattachment of severed fingers and ears, or of the detached scalp, the blood flow needs to be reestablished. This is achieved by reconnecting the major arteries and veins. In particular, the veins can be difficult to find.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings This is where the medicinal leech comes to the rescue. The animals are applied to the tissue and they actively remove blood and secrete numerous compounds that have vasodialator, anticoagulant, and clot-dissolving properties.