17-1 CHAPTER 17 Annelids Annelids

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Characteristics Diversity Annelids exhibit segmentation or metamerism Annelids exhibit segmentation or metamerism Each unit contains components of most organ systems Each unit contains components of most organ systems Evolution of metamerism allowed: Evolution of metamerism allowed: Increased burrowing efficiency Increased burrowing efficiency more sophisticated nervous system more sophisticated nervous system Provided a safety factor Provided a safety factor If one segment failed, others could still function If one segment failed, others could still function

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Classification Class Oligochaeta (Eathworms) Class Oligochaeta (Eathworms) Class Hirudinida (leeches) Class Hirudinida (leeches) Characteristics

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Phylum Annelida Characteristics About 15,000 species About 15,000 species Coelomates - 1st phyla to have true coelom Coelomates - 1st phyla to have true coelom Platyhelminthes = acoelomate Platyhelminthes = acoelomate Nematoda = pseudocoelomate Nematoda = pseudocoelomate EctodermMesodermEndoderm

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Triploblastic Protostome Triploblastic Protostome Complete Gut Complete Gut Platyhelminthes - incomplete Platyhelminthes - incomplete Nematodes- complete Nematodes- complete Have a Circulatory System - closed Have a Circulatory System - closed Heart-like structure : aortic arches Heart-like structure : aortic arches Other worms - no circulatory system Other worms - no circulatory system Setae (se’-tah) Setae (se’-tah) Tiny bristles called setae Tiny bristles called setae Absent in leeches Absent in leeches Short setae anchor segments in earthworms Short setae anchor segments in earthworms Prevent it from slipping backward Prevent it from slipping backward Long setae help aquatic worms swim Long setae help aquatic worms swim Phylum Annelida

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Body Plan Body Wall Body Wall Head is composed of Head is composed of Prostomium Prostomium Terminal portion bearing the anus is the pygidium Terminal portion bearing the anus is the pygidium Head and pygidium are not considered metameres (segments) Head and pygidium are not considered metameres (segments) New metameres form in front of the pygidium New metameres form in front of the pygidium Surface is covered with an epidermis and a thin outer layer cuticle Surface is covered with an epidermis and a thin outer layer cuticle Phylum Annelida

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Phylogeny Traditionally, annelids are divided among 3 classes Traditionally, annelids are divided among 3 classes Class Polychaeta (marine) Class Polychaeta (marine) Class Oligochaeta (earthworms) Class Oligochaeta (earthworms) Class Hirudinida (leeches) Class Hirudinida (leeches) Oligochaeta and Hirudinida Oligochaeta and Hirudinida Characterized by reproductive structure called a clitellum Characterized by reproductive structure called a clitellum Clade clitellata Clade clitellata Phylum Annelida

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Clade Clitellata Class Oligochaeta and Class Hirudinida Class Oligochaeta and Class Hirudinida Form reproductive structure called a clitellum Form reproductive structure called a clitellum Permanent in oligochaetes but visible only during reproductive season in leeches Permanent in oligochaetes but visible only during reproductive season in leeches Hermaphroditic (monoecious) animals Hermaphroditic (monoecious) animals Young develop inside a cocoon secreted by the clitellum, and emerge as small worms Young develop inside a cocoon secreted by the clitellum, and emerge as small worms

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Class Oligochaeta- earthworm Diversity Diversity Over 3000 species Over 3000 species Nearly all have setae (bristle like hairs) Nearly all have setae (bristle like hairs) Form and Function Form and Function Sometimes called “night crawlers” Sometimes called “night crawlers” Burrow in moist rich soil and usually live in branched interconnected tunnels Burrow in moist rich soil and usually live in branched interconnected tunnels Damp, rainy weather: Remain near surface Damp, rainy weather: Remain near surface Dry weather: Burrow deep underground and go dormant coiled in a slime chamber Dry weather: Burrow deep underground and go dormant coiled in a slime chamber Clade Clitellata

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Nutrition Scavengers, feeding on decayed organic matter, leaves, etc. Scavengers, feeding on decayed organic matter, leaves, etc. Food moistened by mouth and drawn in by a sucking action of muscular pharynx Food moistened by mouth and drawn in by a sucking action of muscular pharynx Food is stored in a thin-walled crop Food is stored in a thin-walled crop Muscular gizzard grinds food into small pieces Muscular gizzard grinds food into small pieces Digestion and absorption occur in intestine Digestion and absorption occur in intestine Clade Clitellata

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Circulation and Respiration Circulation and Respiration Coelomic fluid and blood transport food, wastes, and respiratory gases Coelomic fluid and blood transport food, wastes, and respiratory gases Blood circulates in a closed system Blood circulates in a closed system Dorsal vessel and Ventral vessel present. Dorsal vessel and Ventral vessel present. Heart consists of 5 pairs of aortic arches Heart consists of 5 pairs of aortic arches No special gaseous exchange organs No special gaseous exchange organs Gas exchanged across body surface Gas exchanged across body surface Excretion Excretion Each segment, except the 1 st three, have a pair of metanephridia (excretory organ) - releases waste into nephridiopore Each segment, except the 1 st three, have a pair of metanephridia (excretory organ) - releases waste into nephridiopore Clade Clitellata

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Reproduction and Development Reproduction and Development Monoecious (hermaphroditic) Monoecious (hermaphroditic) Reproductive structures are located in segments 9 through 15 Reproductive structures are located in segments 9 through 15 Sperm produced by testes mature in seminal vesicles and pass into sperm ducts Sperm produced by testes mature in seminal vesicles and pass into sperm ducts Eggs are discharged by ovaries Eggs are discharged by ovaries Two pairs of seminal receptacles receive and store sperm Two pairs of seminal receptacles receive and store sperm Clade Clitellata

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Mate at night during warm, moist weather Mate at night during warm, moist weather Aligning in opposite directions, ventral surfaces together Aligning in opposite directions, ventral surfaces together Mucus secreted by clitellum holds worms together Mucus secreted by clitellum holds worms together Sperm from each worm are transported to the seminal receptacles of the other along seminal grooves Sperm from each worm are transported to the seminal receptacles of the other along seminal grooves After mutual copulation, each worm secretes a mucus tube to form a cocoon After mutual copulation, each worm secretes a mucus tube to form a cocoon Cocoon passes forward and eggs, and sperm are added Cocoon passes forward and eggs, and sperm are added Fertilization and embryogenesis occur in cocoon Fertilization and embryogenesis occur in cocoon Young worms emerge from cocoon Young worms emerge from cocoon Clade Clitellata

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Class Hirudinida: Leeches Hirudinea Hirudinea 34 segments, lack setae but possess anterior and posterior suckers 34 segments, lack setae but possess anterior and posterior suckers Diversity Diversity Most freshwater, few marine or live in moist terrestrial environments Most freshwater, few marine or live in moist terrestrial environments More common in the tropics temperate zones More common in the tropics temperate zones Vary in color: black, brown, red, and olive green Vary in color: black, brown, red, and olive green Some carnivores feeding on small invertebrates Some carnivores feeding on small invertebrates Others are temporary or permanent parasites Others are temporary or permanent parasites Hermaphroditic Hermaphroditic Form a clitellum during breeding season Form a clitellum during breeding season Secretes a cocoon for reception of eggs Secretes a cocoon for reception of eggs Clade Clitellata

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Largest Leech Gut specialized for storage of large quantities of blood

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Nutrition Nutrition Not all are parasites, many are predators Not all are parasites, many are predators Freshwater leeches have a proboscis (pharynx) for ingesting small invertebrates as well as to suck blood Freshwater leeches have a proboscis (pharynx) for ingesting small invertebrates as well as to suck blood Some terrestrial leeches feed on insect larvae, earthworms, and slugs Some terrestrial leeches feed on insect larvae, earthworms, and slugs Other terrestrial leeches climb trees or bushes to reach warm-blooded vertebrates such as baby birds Other terrestrial leeches climb trees or bushes to reach warm-blooded vertebrates such as baby birds Most are fluid feeders that prefer tissue fluids and blood pumped from open wounds Most are fluid feeders that prefer tissue fluids and blood pumped from open wounds Clade Clitellata

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Medicinal Leech: Used to relieve congestion in the veins due to injury.