Phylum Annelida

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Phylum Annelida

• the segmented worms

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Activities and Assignments

• Labs
• Earthworm behavior (binder)
• Earthworm Dissection (binder)
• Video Med. Uses of Leeches (binder)
• Quiz- short topic
• Text Reading 671-674
• Worksheet
• Vocabulary monecious, dioecious, mutualism,
  tagmosis, detritus, triploblastic, coelom, septa,
  cerebral ganglia, parapodia, setae, parts of the
  worm anatomy from the lab

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How do the Annelids fit in?
Annelida
Rotifera
Nematoda
Platyhelminthes
Nemertea
Cnidaria
Porifera
unknown common ancestor
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Annelida Characteristics
Triploblastic (3 tissue layers)
Organ level of organization
Bilateral Symmetry
Cephalization
Coelomate (with a body cavity)
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Remember these ideas from the last chapter
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Coelomate
Have a true body cavity that is completely
surrounded by mesoderm
ectoderm
coelom
mesoderm
endoderm
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Annelid Characteristics
the coelom

• is a closed, fluid filled cavity that surrounds
  the gut
• the fluid within acts as a circulatory system
  and hydroskeleton
• mesodermal membranes (mesenteries) suspend
  organs in the coelom

ectoderm
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Annelida Characteristics
Metamerism

• The body is made up of serially repeating,
  coordinated segments called metameres that are
  separated from one another by septa.
• Each metamere contains sets of repeating organs
• e.g. gut, blood vessels, nerve cord, excretory
  organs

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Metamerism
septa
Think of a row of tires
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Annelida Characteristics
Nervous system

• 2 cerebral ganglia
• a ventral nerve cord with 2 ganglia per
  metamere.
• In some species, sensory organs such as eyes,
  palps, and tentacles have arisen

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brain
nerve cord
2 cerebral ganglia
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Annelida Characteristics
Arthropod exoskeleton component
Locomotion

• both longitudinal and circular muscles
• most have setae (chitonous bristles secreted by
  the epidermis) that aid in locomotion and
  burrowing

Skeletal System

• fluid in coelom acts as a hydrostatic skeleton

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Class Oligochaeta
Locomotion
Circular muscle contraction
Longitudinal muscle contraction
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Annelind Cross section
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Annelind Cross section
Circular muscle
Longitudinal muscle
skin
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Annelind Cross section
coelom
Circular muscle
Gut (intestine)
Longitudinal muscle
Intestine wall
skin
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Annelid Characteristics
Gas exchange

• mainly by diffusion
• Class Polychaeta often has specialized
  structures for gas exchange
• (e.g. parapodia, gills)

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Annelid Characteristics
Digestive System
Youll get to observe these more closely during
the dissection

• complete
• regional specialization

Circulatory System

• closed circulatory system composed of blood
  vessels (some of which are contractile and act as
  hearts)
• some circulation is also accomplished by the
  coelomic fluid

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coelomic chambers
pharynx
mouth
esophagus
crop (storage)
gizzard (mashing)
This diagram is found in the dissection lab
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More properly called aortic arches
One each on the dorsal and ventral sides
hearts
blood vessels
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Annelid Characteristics
Excretion

• excretion is accomplished by organs called
  nephridia (singular nephridium) in the skin
• sexual
• Hermaphrodites (individuals with both sets of
  reproductive organs)

Reproduction
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Phylum Annelida
Class Oligochaeta Class Hirudinea Class
Polychaeta
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Class Oligochaeta
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Class Oligochaeta

• terrestrial, freshwater and marine
• have few setae (Oligo few, chaeta setae)
• usually feed on detritus
• (decaying organic matter)
• have specialized digestive system to obtain the
  maximum amount of nutrients out of the detritus
  (e.g. pharynx, gizzard, crop)

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Class Oligochaeta
Locomotion
Circular muscle contraction
Longitudinal muscle contraction
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Class Oligochaeta
Reproduction

• usually monoecious
• cross-fertilize by
• exchanging sperm

clitellum
testis
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Ecology

• Earthworms are essential soil aerators
• If all the material ever moved through
  earthworms was piled up, the heap would rise
  30miles , more than 5 times the height of Mount
  Everest!!
• Worm Grunting

A saw or leaf spring of a pick-up
stob
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Class Hirudinea
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Class Hirudinea

• usually freshwater but there are some marine and
  terrestrial species
• no septa between metameres
• no setae
• have 2 suckers

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Class Hirudinea

• have an extendable proboscis for feeding

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Class Hirudinea

• usually have a fixed number of segments (34)
• each metamere consists of several annuli (think
  accordion)

1 metamere
annuli
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Class Hirudinea
Locomotion
Lack septa between metameres, so they are
incapable of moving like Oligochaetes. Instead,
they use their anterior and posterior suckers to
move.
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Class Hirudinea
Reproduction

• usually monoecious
• cross-fertilize by
• exchanging sperm

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Ecology

• Although some leeches are parasitic blood
  suckers (can be temporary or permanent), many are
  predators.

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Ecology
video

• Leeches have been used medicinally since the
  19th century.
• Currently they are used to increase blood flow
  following reconstructive surgery
• Hirudin is a powerful anticoagulant that is
  found in the salivary glands of leeches
• Leech saliva contains antiseptic chemicals
• And an anesthetic

DONT WRITE THIS DOWN, YOU HAVE AN ARTICLE AND
VIDEO WITH THE INFO
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Class Polychaeta
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Class Polychaeta

• all marine
• this class contains 2/3 of all known Annelids
• have a well developed head with specialized
  sense organs

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Class Polychaeta

• have many setae (chitonous bristles secreted by
  the epidermis)
• (Poly many, chaeta setae)
• these setae are arranged in bundles on
  paddle-like appendages called parapodia

setae
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Class Polychaeta
Parapodium
setae
The parapodia function in gas exchange,
locomotion, and feeding.
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Class Polychaeta

• Tagmatization (tagmosis)
• the fusion and specialization of formerly
  metameric segments

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Class Polychaeta
Many are filter-feeders with specialized
structures
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Class Polychaeta
Many are predatory with specialized structures
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Class Polychaeta
Many construct their own homes out of CaCO3 or
sand debris and mucous
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Class Polychaeta

• Reproduction
• usually dioecious (separate sexes)
• no permanent sex organs gametes are shed into
  coelom
• fertilization is usually external
• indirect development ? trocophore larvae

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Ecology

• Polychaetes often have effective
• defense strategies
• some have tubes to hide in
• some have vicious jaws
• some have modified stinging setae

a fireworm
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Ecology
A type of symbiosis

• Some Polychaetes have a mutualistic relationship
  with their host
• for example, many scaleworms are found near, or
  in the mouth, of brittlestars, starfish, and sea
  urchins.
• The scaleworm eats its hosts leftovers and with
  its vicious jaws, it will attack any predator
  trying to eat its host.

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How do the Annelids fit in?
Oligochaeta
Hirudinea
Polychaeta
Nematoda
Rotifera
metamerism
Nemertea
Platyhelminthes
Cnidaria
Porifera
eucoelomate
protostome
unknown common ancestor
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Segmented Worm Quiz on

• Topics
• Phylum Annelida and 3 classes
• General Characteristics and Examples of each
• Vocabulary monecious, dioecious, mutualism,
  tagmosis, detritus, triploblastic, coelom, septa,
  cerebral ganglia, parapodia, setae, parts of the
  worm anatomy from the lab
• Labs
• Earthworm behavior (binder)
• Earthworm Dissection (binder)
• Video Med. Uses of Leeches (binder)
• Quiz- short topic
• Text Reading 671-674
• Worksheet