17-1 chapter 17 annelids annelids. copyright © the mcgraw-hill companies, inc. permission required...
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CHAPTER 17CHAPTER 17CHAPTER 17CHAPTER 17
AnnelidsAnnelids AnnelidsAnnelids
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CharacteristicsCharacteristics
DiversityDiversity Annelids exhibit segmentation orAnnelids exhibit segmentation or metamerism metamerism
Each unit contains components of most organ Each unit contains components of most organ systemssystems
Evolution of metamerism allowed:Evolution of metamerism allowed: Increased burrowing efficiencyIncreased burrowing efficiency more sophisticated nervous systemmore sophisticated nervous system Provided a safety factorProvided a safety factor
If one segment failed, others could still functionIf one segment failed, others could still function
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ClassificationClassification Class Oligochaeta (Eathworms)Class Oligochaeta (Eathworms) Class Hirudinida (leeches)Class Hirudinida (leeches)
CharacteristicsCharacteristics
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Phylum AnnelidaPhylum Annelida
CharacteristicsCharacteristics About 15,000 species About 15,000 species CoelomatesCoelomates - 1st phyla to have true coelom - 1st phyla to have true coelom
Platyhelminthes = acoelomatePlatyhelminthes = acoelomate Nematoda = pseudocoelomateNematoda = pseudocoelomate
EctodermEctodermMesodermMesodermEndodermEndoderm
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Triploblastic ProtostomeTriploblastic Protostome Complete GutComplete Gut
Platyhelminthes - incompletePlatyhelminthes - incomplete Nematodes- completeNematodes- complete
Have a Circulatory System - closedHave a Circulatory System - closed Heart-like structure : aortic archesHeart-like structure : aortic arches Other worms - no circulatory systemOther worms - no circulatory system
Setae (se’-tah)Setae (se’-tah) Tiny bristles called setaeTiny bristles called setae Absent in leechesAbsent in leeches Short setae anchor segments in Short setae anchor segments in
earthworms earthworms Prevent it from slipping backwardPrevent it from slipping backward
Long setae help aquatic worms swimLong setae help aquatic worms swim
Phylum AnnelidaPhylum Annelida
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Body PlanBody Plan Body WallBody Wall
Head is composed ofHead is composed of Prostomium Prostomium
Terminal portion bearing the anus is theTerminal portion bearing the anus is the pygidium pygidium Head and pygidiumHead and pygidium are not considered metameres are not considered metameres
(segments)(segments) New metameresNew metameres form in front of the pygidium form in front of the pygidium Surface is covered with an epidermis and a thin Surface is covered with an epidermis and a thin
outer layer cuticle outer layer cuticle
Phylum AnnelidaPhylum Annelida
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17-7 Marine Annelids
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CoelomatesCoelomates
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PhylogenyPhylogeny Traditionally, annelids are divided among Traditionally, annelids are divided among 3 3
classesclasses Class Polychaeta (marine)Class Polychaeta (marine) Class Oligochaeta (earthworms)Class Oligochaeta (earthworms) Class Hirudinida (leeches)Class Hirudinida (leeches)
Oligochaeta and HirudinidaOligochaeta and Hirudinida Characterized by reproductive structure Characterized by reproductive structure
called a called a clitellumclitellum Clade clitellata Clade clitellata
Phylum AnnelidaPhylum Annelida
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Clade ClitellataClade Clitellata
Class Oligochaeta and Class HirudinidaClass Oligochaeta and Class Hirudinida Form reproductive structure called a Form reproductive structure called a
clitellumclitellum Permanent in oligochaetes but visible only Permanent in oligochaetes but visible only
during reproductive season in leechesduring reproductive season in leeches HermaphroditicHermaphroditic (monoecious) animals (monoecious) animals Young develop inside a cocoon Young develop inside a cocoon
secreted by the clitellum, and emerge secreted by the clitellum, and emerge as small wormsas small worms
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Class Oligochaeta- earthworm Class Oligochaeta- earthworm DiversityDiversity
Over 3000 species Over 3000 species Nearly all have Nearly all have setae setae (bristle like hairs)(bristle like hairs)
Form and FunctionForm and Function Sometimes called “night crawlers”Sometimes called “night crawlers” Burrow in moist rich soil and usually live in Burrow in moist rich soil and usually live in
branched interconnected tunnelsbranched interconnected tunnels Damp, rainy weather:Damp, rainy weather: Remain near surface Remain near surface Dry weather:Dry weather: Burrow deep underground and Burrow deep underground and
go dormant coiled in a slime chambergo dormant coiled in a slime chamber
Clade ClitellataClade Clitellata
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NutritionNutrition Scavengers,Scavengers, feeding on decayed organic matter, feeding on decayed organic matter,
leaves, etc.leaves, etc. Food moistened by mouth and drawn in by a Food moistened by mouth and drawn in by a
sucking action of muscular pharynxsucking action of muscular pharynx Food is stored in a thin-walled Food is stored in a thin-walled cropcrop Muscular Muscular gizzardgizzard grinds food into small pieces grinds food into small pieces Digestion and absorption occur in intestineDigestion and absorption occur in intestine
Clade ClitellataClade Clitellata
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Circulation and RespirationCirculation and Respiration Coelomic fluid and bloodCoelomic fluid and blood transport food, wastes, and transport food, wastes, and
respiratory gasesrespiratory gases Blood circulates in a Blood circulates in a closed systemclosed system Dorsal vesselDorsal vessel and and Ventral vesselVentral vessel present. present. Heart consists of 5 pairs of Heart consists of 5 pairs of aortic archesaortic arches No special gaseous exchange organs No special gaseous exchange organs
Gas exchanged across body surfaceGas exchanged across body surface
Excretion Excretion Each segment, except the 1Each segment, except the 1stst three, have a three, have a pair of pair of
metanephridia (excretory organ) - metanephridia (excretory organ) - releases waste intoreleases waste into nephridioporenephridiopore
Clade ClitellataClade Clitellata
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17-15Excretory System
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Nervous System: Brain, Nerve Cord, Peripheral
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Nerve Cord
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Reproduction and DevelopmentReproduction and Development Monoecious (hermaphroditic)Monoecious (hermaphroditic) Reproductive structures are located in Reproductive structures are located in
segments 9 through 15segments 9 through 15 Sperm produced by testes mature in Sperm produced by testes mature in
seminal vesicles and pass into sperm seminal vesicles and pass into sperm ductsducts
Eggs are discharged by ovariesEggs are discharged by ovaries Two pairs of seminal receptacles receive Two pairs of seminal receptacles receive
and store sperm and store sperm
Clade ClitellataClade Clitellata
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Mate at night during warm, moist weatherMate at night during warm, moist weather Aligning in Aligning in opposite directions,opposite directions, ventral surfaces ventral surfaces
togethertogether Mucus secreted by Mucus secreted by clitellumclitellum holds worms together holds worms together Sperm from each worm are transported to the Sperm from each worm are transported to the
seminal receptaclesseminal receptacles of the other along of the other along seminal seminal groovesgrooves
After mutual copulation, each worm secretes a After mutual copulation, each worm secretes a mucus tube to form a mucus tube to form a cocooncocoon
Cocoon passes forward and Cocoon passes forward and eggs, and sperm are eggs, and sperm are addedadded
Fertilization and embryogenesisFertilization and embryogenesis occur in cocoon occur in cocoon Young wormsYoung worms emerge from cocoon emerge from cocoon
Clade ClitellataClade Clitellata
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Class Hirudinida: LeechesClass Hirudinida: Leeches
HirudineaHirudinea 34 segments34 segments, lack setae but possess anterior and posterior , lack setae but possess anterior and posterior
suckerssuckers Diversity Diversity
Most freshwater,Most freshwater, few marine or live in moist terrestrial environments few marine or live in moist terrestrial environments More common in the tropicsMore common in the tropics temperate zones temperate zones Vary in color:Vary in color: black, brown, red, and olive green black, brown, red, and olive green Some carnivoresSome carnivores feeding on small invertebrates feeding on small invertebrates Others are Others are temporary or permanent parasitestemporary or permanent parasites Hermaphroditic Hermaphroditic Form a Form a clitellumclitellum during breeding season during breeding season
Secretes a cocoon for reception of eggsSecretes a cocoon for reception of eggs
Clade ClitellataClade Clitellata
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Largest Leech
Gut specialized Gut specialized for storage of for storage of
large quantities large quantities of bloodof blood
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2 suckers:Posterior
and Anterior
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Nutrition Nutrition Not all are parasites, Not all are parasites, many are predatorsmany are predators Freshwater leeches have a proboscis (pharynx) for Freshwater leeches have a proboscis (pharynx) for
ingesting small invertebrates as well as to suck ingesting small invertebrates as well as to suck bloodblood
Some terrestrial leeches feed on insect larvae, Some terrestrial leeches feed on insect larvae, earthworms, and slugsearthworms, and slugs
Other terrestrial leeches climb trees or bushes to Other terrestrial leeches climb trees or bushes to reach warm-blooded vertebrates such as baby reach warm-blooded vertebrates such as baby birdsbirds
Most are Most are fluid feedersfluid feeders that prefer tissue fluids and that prefer tissue fluids and blood pumped from open woundsblood pumped from open wounds
Clade ClitellataClade Clitellata
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Medicinal Leech: Used to relieve congestion in the veins due to injury.