Transcript Class Hirudinomorpha

Biology 320
Invertebrate Zoology
Fall 2005
Chapter 13 – Phylum Annelida
Part Two
Taxon Clitellata
 Two classes
 Class Oligochaeta
 Class Hirudinomorpha
 Posses a clitellum
 Several (6 or 7 in Lumbricus) anterior
segments with a thick, glandular
epidermis
 Conspicuous during reproduction
 Close proximity to gonopores
 Produces mucus for copulation, albumen
for eggs, and cocoons
 Lack parapodia, prostomial and pygidial
appendages
 Copulating hermaphrodites with direct
development
Class Oligochaeta
 Name means “few chaetae”
 3500 spp.
 Earthworms are most familiar,
but also small FW and marine
varieties
 200 marine spp., mostly
interstitial
 Giant Australian earthworm
(Megascolides australis)
 Up to 3 m long
Body Form
 Only exceptions to generalized
annelid are listed
 Four bundles of chaetae per
segment
 Two ventral
 Two lateral
 Chaetae are structurally simple
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Genital chaetae are more complex
One to 25 chaetae per bundle
Two per bundle in most earthworms
Protractor and retractor muscles
attached to each chaeta
 Small in terrestrial varieties and
longer in aquatics
Coelom
 Earthworms posses coelomopores
 Connect coelomic cavities with exterior
 Posses a sphincter
 Pores are located in intersegmental furrows
 Exude coelomic fluid dorsally
 Keeps animal moist
 Deters predators
 “Squirter worm” (Didymogaster) can squirt fluid 30 cm high
Locomotion
 Crawl or burrow using peristalsis
 Mucus and egested soil coat
burrow walls
 Lumbricus terrestris covers
burrow opening
 Larger worms can burrow deeper
 Chaetae are extended or
retracted as needed to apply
optimal traction
 Animal moves forward in steps
 2 – 3 cm per step
 Approximately 30 cm per minute
in some
 Can even crawl backwards
Nutrition
 Scavengers of dead organic
matter (such as leaves) and / or
deposit feeders
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Swallow soil
Takes 1 – 2.5 hr to process
Castings are excreted
Great for soil (aerates, mixes,
and transfers nutrients)
 Aquatic varieties may be
carnivores of amebas, ciliates,
rotifers, etc.
 Some may parasitize FW snails
Nervous System
 One large ventral nerve cord instead of two lateral cords
 Five giant axons
 Stimulation of either end of worm elicits an escape response
(wriggling, or withdrawal into burrow)
 Subpharyngeal ganglion is motor control center
 Most lack eyes but have simple ocelli
 Some have rings of chemoreceptors (called tubercles) that project
from cuticle
Digestive System
 Pharyngeal bulb
 Eversible in aquatic spp.
 Muscular pump in terrestrial
spp.
 Esophageal glands secrete
mucus and enzymes
 Compartmentalized
esophagus
 Crop for food storage
 Gizzard for grinding
 Lined with chitin-like cuticle
Calciferous Glands
 Located in wall of esophagus
 Produce calcite crystals that are secreted into
esophageal lumen and pass in feces
 Two functional hypothesis
 1) Removal of excess CO2
 Soil CO2 is high (relative to atmospheric levels), due to bacterial
respiration
 Therefore there is a negative concentration gradient for diffusion of
worm’s CO2
 CO2 combines with calcium ions to form calcite
 2) Removal of excess calcium
Digestive System Cont…
 Intestine makes up posterior 3/4 of
digestive system
 Anterior half secretes digestive
enzymes
 Cellulase and chitinase (breaks down
fungal cell walls) are released by
mutualistic bacteria
 Posterior half is absorptive
 Typhlosole is a large dorsal fold in the
intestine that increases its surface area
 Chlorogogen cells surround intestine
 Waste - laden cells are released into
coelom
 Exit body via nephridiopores or
coelomopores
Circulation and Gas Exchange
 Often have hearts (described
earlier)
 Five pairs in Lumbricus
(segments 7-11)
 Gas exchange is carried out
across body wall
 Large species have capillary
loops in epidermis and
hemoglobin dissolved in plasma
 Moist surface facilitates diffusion
 Oxygen levels in soil drop after
heavy rains, forcing earthworms
to the surface
Excretion
 Ureotelic but excrete some ammonia
 Depends on environmental conditions
 Osmoregulation
 Urine is hyposmotic
 Often several types of nephridia
 Allows them to tolerate dry soils
 Those without special nephridia must burrow
deeper during dry periods
Encystment
 Can secrete tough mucus covering
 Summer cysts to avoid desiccation
 Winter cysts during periods of low temperature
 Undergo diapause
 Some migrate deeper into soil during dry or
cold periods
 Up to three meters down in some
 70% of body water can be lost
Reproduction
 Clonal reproduction always occurs via transverse fission
 Sexual
 Monoecious (hermaphroditic)
 Reproductive organs located in a few anterior segments
 Paired ovaries release eggs which develop in ovisacs
 Paired testes release sperm which develop in seminal vesicles
 Genital segments each posses a pair of gonoducts (sperm ducts
or oviducts), which open to the ventral surface
 Female genital segments have ventral openings that lead to
seminal receptacles (store sperm prior to fertilization)
 Lumbricus breeds continually, but
some have one yearly reproductive
season
 Often reabsorb reproductive system
and grow back later
 Copulation with mutual sperm
transfer
 Ventral contact between oppositely
oriented worms
 Genital chaetae and mucus produced by
clitellum hold worms together
 Sperm swim in a ventral sperm
groove from male gonopores to
openings of partner’s seminal
receptacles
 Indirect sperm transfer
 Entire process can take 2 – 3 hours
 Some worms have copulatory organ
for direct sperm transfer
 Secreted a few days after
copulation
 Clitellum secretes mucus tube
 Clitellum secretes chitinous
material which becomes wall of
cocoon
 Albumen from clitellum deposited
into cocoon
 Tube slides forward as worm
moves backwards
 Eggs and partner’s sperm (from
seminal receptacles) deposited
into cocoon
 External fertilization
 Cross fertilization
 Cocoon slides of head, and ends
pinch off; mucus tube
disintegrates
Cocoons
 Terrestrial species deposit
cocoons in soil
 Aquatic species deposit
cocoons in debris or mud, or
attach to vegetation
 Ovoid and yellow in color
 Contain 1 to 20 eggs
 7.5 cm X 2 cm in
Megascolides
Development
 Direct development
 Therefore create eggs containing yolk or albumen
 Eight days to several months before juveniles
emerge from cocoons
 Live several years
 Six years in captivity
 Reach sexual maturity at approximately 200
days
Class Hirudinomorpha
 Leeches and closely related worms
 500 spp
 Marine, mostly freshwater, a few
terrestrial species (restricted to moist
environments)
 Lack chaetae
 Have a fixed number of segments
(typically 33)
 All have a posterior sucker for adhering
to prey or substratum
 Most have an anterior sucker as well
 Blood-sucking ectoparasites or
carnivores
 1 cm to 30 cm long
(Haementeria, giant Amazonian
leech)
 Black, brown, olive, or red in
color
 May have striped / spotted
patterns
 Typically inhabit stagnant or
slow moving freshwater
 Estivate in mud during periods
of drought
 Can lose 90% of body water
 Often extremely abundant
Body Form
 Dorsoventrally flattened
 Tapered at anterior end
 Suckers
 Anterior (if present) is smaller and surrounds
mouth
 Posterior is disc-shaped; anus located directly
anterior
 Annulations that don’t accurately depict
segments
 Number of annulations per segment varies
 Clitellum spans segments 9-11, but is only
conspicuous during reproduction
Body Wall
 Connective tissue is
much thicker
 Makes up a larger
proportion of the animal
 Slightly different
musculature
 Dorsoventral muscles
 For flattening
 Helical muscles
 For twisting
 Larger connective tissue
compartment means a
reduction of the coelom
 Lack septa, so therefore lack
bilateral coelomic cavities
 Also lack mesenteries
 Continuous coelom which
serves as a hemal system
 Two large lateral coelomic
vessels
 Dorsal and ventral coelomic
vessels
 Lined with mesothelium
(chlorogogen cells)
 Muscle contractions propel fluid
 Body surface conducts gas
exchange
Coelom
Locomotion
 Not equipped for burrowing due to:
 Reduction of coelom
 Loss of septa and chaetae
 Many inchworm by anchoring with anterior and posterior suckers
 Many swim
 First contract dorsoventral muscles to increase surface area
 Then undulate
Nervous System
 Similar to other annelids
 Fusions of ganglia in the sucker regions
 Posses ocelli
 Posses sensory papillae
 Projecting discs consisting of many sensory cells
 Typically found dorsally, in rows, on one annulation of a particular
segment
 Sense organs mainly used for prey detection, and respond to:
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Moving shadows and water-pressure vibrations in fish leeches
Chemicals from body fluids such as oils, sweat, and blood
Waves
Temperature differences
Excretory System
 10 – 17 pairs of metanephridia
 One pair per segment in middle 1/3 of animal
 Nephrostomes project into coelomic vessels
 Nephridial tubules are embedded in connective
tissue
 Posses a bladder that fills before urine is released
through nephridiopore
 Important for osmoregulation
Digestive System
 Pharynx types
 Protrusible pharynx that is forced
into prey / host tissue
 Non-protrusible sucking pharynx
 May or may not have jaws
 Enzymes usually facilitate
penetration in those lacking jaws
 Salivary glands empty secretions
into pharynx
 Hirudin – anticoagulant
 Anesthetic
 Vasodilators
 Often 1 – 11 pairs of lateral
intestinal ceca
Nutrition
 Three fourths are
blood suckers
 Usually not host
specific
 Usually parasitize a
group of organisms
(i.e. crayfish, fish,
reptiles, birds,
mammals, etc.)
 Some are carnivores
of small invertebrates
 Water from plasma is
excreted via nephridiopores
 Digestion is very slow
 Gut produces hardly any
enzymes
 Symbiotic bacteria may
produce digestive enzymes
and vitamins
 May take 200 days to digest a
blood meal
 Rarely feed
 One blood meal may increase
animals weight by 10X
 May only need to feed twice a
year in order to grow
 Some can fast for 1.5 years
Medical Applications
 Historically used in Europe for
bloodletting
 Supposedly, George Washington
died two days after a bloodletting
for a soar throat
 Hirudo medicinalis is still used
today for restoring circulation and
reducing swelling after:
 Skin grafts
 Digit / appendage reattachment
 Natural antibiotic properties
 Symbiotic bacteria produce
antibiotics to reduce competition
with other bacteria
Reproduction
 No sexual reproduction, including regeneration
 Hermaphroditic, but not simultaneous
 Protandric
 Male portion of reproductive system develops first
 Spend first part of existence as males, then later reproduce as
females
 Copulation and fertilization is always internal
 Most have copulatory organ for direct sperm transfer
 Others hypodermically impregnate using a spermatophore
 Pressure and cytolytic chemicals rupture body wall of mate
 Sperm are released and migrate toward eggs
 Eggs are laid after copulation
 Time varies
 Clitellum secretes a cocoon and albumen
 The cocoons of fish leeches are attached to
fish hosts
 Some brood eggs by attaching cocoon to
substratum and ventilate eggs by fanning
flattened ventral surface
 Some attach cocoon to ventral surface