Transcript Biology 320 Invertebrate Zoology Fall 2005

Biology 320
Invertebrate Zoology
Fall 2005
Chapter 22 –
Phylum Gastrotricha and
Phylum Nematoda
Phylum Gastrotricha

500 species
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Found in all three habitat
types
– Marine and FW interstitially or on plants
– Terrestrially - in water film
covering soil particles
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Microscopic to 4mm long
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Eutelic
– Genetically predetermined
and constant number of
cells
– Cell size increases, but not
cell number
Body Form
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Bowling-pin-shaped
– Name means “hairy belly”
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Locomotory cilia on
ventral surface
Adhesive tubes located
near head and/or on
lateral body
– Adhesive organs at
posterior
– All are similar to duoglands of turbellarians
Body Wall
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Cuticle
– Not chitinous
– Not molted
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Epidermis
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Musculature
– Circular
– Longitudinal
Organ Systems
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No hemal system
– Acoelomate, so don’t even possess a hemocoel
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No respiratory system
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Nervous system
– Brain
– Pair of ventrolateral nerve cords
– Sensory organs
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Cerebral organs possess all three types of receptors
Sensory bristles found on body surface
Excretory system
– One to several pairs of protonephridia
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Nephridiopores open ventrolaterally
Osmoregulatory in function
– Ammonotelic, so ammonia diffuses across body surfaces
Movement
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Ciliary gliding for
forward movement
Rapid rearward
withdrawal as an
escape response
Can use a combination
of adhesion and
muscular contractions
to:
– Inchworm
– Somersault
Nutrition
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Gut lacks stomach
Large muscular
pharynx
– Y-shaped in some
– Possess pharyngeal
pores that open to
surface and release
excess ingested water
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Feed on small organic
particles (live or dead)
– Bacteria and protozoans
Reproduction

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Hermaphroditic with indirect sperm
transfer
Posterior copulatory organ that is loaded
with sperm from anterior male gonopore
Spermatophore transferred to seminal
receptacle via posterior female gonopore
– Internal fertilization

Fertilized eggs are released by
rupturing body wall
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Some species are parthenogenic
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Can produce two types of eggs
– Summer
– Winter (resting)
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Direct development
Sexual maturity is reached in about
three days
Life span is approximately 40 days
Phylum Nematoda
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Roundworms
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20,000 described species
– May be the largest animal
phylum
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Found worldwide and live
in all habitat types
– Interstitially
– Inside of animals and
plants
– 53°C hot springs
– Epiphytic bromeliads
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Very abundant
– One cubic meter of mud
off of the coast of Holland
contains over 4,000,000
nematodes

Ecologically important
– Link between
decomposers and higher
trophic levels
– Some are excellent
decomposers and nutrient
cyclers
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90,000 nematodes in one
rotting apple
Caenorhabditis elegans is
an important model
organism for genetics /
development studies
Eutelic
– C. elegans has 1031 cells
Body Form

Vermiform
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Tapered at both ends
– Important adaptation for
living interstitially
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Microscopic to 50 cm
– One mm is typical
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Mouth at anterior end, with
three to six lips that bear
sensilla
Caudal gland on posterior
that is similar to a duogland
Lack cilia
Body Wall
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Cuticle
– Not chitinous
– Often annulated
– Must be molted
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Epidermis
–
–
–
–
Secretes cuticle
Stores nutrients
Endoparasites may absorb nutrients with
Has four longitudinal extensions called epidermal cords
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Molted four times while growing
Molting ceases upon reaching adulthood
Ecdysone controls molting
Longitudinal nerve cords housed here
Musculature
– Four bands of longitudinal fibers separated by epidermal cords
– No circular muscles
Locomotion
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Use sinusoidal undulations
of dorsoventral plane to
move forward
– Alternate contractions of
dorsal and ventral
longitudinal muscles
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Efficient movement requires
a substratum to act against
– Removing worms from
natural substratum hinders
locomotion
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Many swim or are capable
of swimming
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Some crawl like earthworms
or inchworms
Organ Systems
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Hemal system
– Large nematodes have a hemocoel (pseudocoel)
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Fluid filled and fluid may contain hemoglobin
Functions as hydrostat
– Small varieties are acoelomate
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No respiratory system
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Nervous system
– Collar-like brain surrounds pharynx
– Dorsal, ventral, and lateral longitudinal nerve cords in
epidermal cords
– Sensory organs
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Papillae – low projections of cuticle on lips and head
Tactile setae
Ocelli – one on each lateral aspect, near pharynx
Nutrition
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Will eat just about
anything
– Carnivorous, herbivorous,
or omnivorous
– Will eat bacteria, protists,
fungi, other nematodes,
and plant cells
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Some are deposit or
detritus feeders
– Actually feed on bacteria
associated with these
types of organic matter
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Some fungi actually prey
on nematodes
– Trap them with hyphal
threads
Digestive System
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Similar to that of gastrotrichs
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Cuticle of foregut contains
teeth, ridges, rods, or plates
– Varies according to feeding
habits
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Example: Mononchus uses
teeth to latch onto other
nematodes
Body contents are pumped out
Will eat over 1000 nematodes
over its 14 week life span
– Diagnostic tool for taxonomists
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Herbivores have a stylet for
piercing plant cells
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Some parasites use body
surface to absorb nutrients
Excretory System
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Ammonotelic
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All have one or more excretory glands
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Some also have an excretory canal system
– Interestingly, is formed from one huge H-shaped cell
– Pore opens midventrally near pharynx
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The canal system is osmoregulatory in C. elegans,
but other nematodes secrete different substances
–
–
–
–
Gelatinous matrix for eggs
Glycoprotein coat for cuticle
Digestive enzymes to erode host tissue in animal parasites
Molting fluid
Reproduction

Most gonochoric
– Some hermaphroditic
– Some parthenogenic
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Internal fertilization with
copulation
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Sexually dimorphic
– Males smaller than female
– Male has curled posterior that
resembles a hook
– Male has a cloaca, as where
vagina is located midventrally
on the middle of the female’s
body
– Male has copulatory spicules
(resemble curved blades) that
are used to hold female
gonopore open
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Both male and female have
C-shaped gonads
Females produce
pheromones to attract
males
Sperm are aflagellate and
amoeboid
Eggs have characteristic
shapes, and experts can
diagnose infections
Some free-living types,
such as Turbatrix, are
viviparous
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Hermaphroditic varieties typically self-fertilize and rarely
cross-fertilize
– Little genetic recombination
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Egg numbers vary greatly between species
– 50 in some marine species
– 200,000 per day in the parasite Ascaris
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Eutelic
– Around 1000 cells
– Number of cells in individual organs is also constant
– Cells grow in size, not in number
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Direct development
– Egg, three juvenile instars, and adult
– Four molts (first two of which may occur in egg before
hatching)
– Molting ceases upon reaching adulthood
Parasitism
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Can be ectoparasites
or endoparasites
Can have one host or
multiple hosts
Can infect plants,
animals, or both
Juveniles, adults or
both can be infective
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Ascaroid nematodes
– Ascaris, hookworms, pinworms, and
Trichinella
– Infect one host: humans, cats, dogs, pigs,
cows, etc.
– Infection occurs when eggs or juveniles are
ingested
 Eggs
hatch in intestine
 Juveniles penetrate intestinal wall
 Juveniles enter hemal system
 Juveniles break through alveoli in lungs
 They migrate up respiratory tree
 Are coughed up in sputum
 If sputum is swallowed, end up in intestine
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Ascaris
– Human intestinal worm: Ascaris
lumbricoides
– Can reach 50 cm in length
– Widely distributed, but is found in SW
US
– Eggs found in soil and are resistant to
harsh environmental conditions
– Children are susceptible to infection
because they put things in their mouths
– Feeds on fluid gut contents of host
– Can cause malnutrition and death in the
event of intestinal blockage
– Secrete substances which inhibit host
digestive enzymes from harming them
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Hookworms
– Necator americanus
– Juveniles enter through skin of
foot
– Follow typical ascaroid path
– Attach to intestinal lining with
hooks
– Feed on host’s blood
– Infections of more than 25
worms can lead to serious blood
loss and tissue damage
– Common in tropics
– 380 million infected worldwide
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Pinworms
– Enterobius vermicularis
– Typically infect humans
– Worldwide distribution
– Adults live in intestine
– At night, female crawls
out anus and deposits
eggs
– Scratching traps eggs
under fingernails
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Trichinella spiralis
– Infects mammals with a condition
known as trichinosis
– Juveniles are carried to skeletal
muscles by blood
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Form calcified cysts in muscle
– Transmitted when undercooked
flesh is eaten
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Example: humans eating
undercooked pork
– Severe infection causes pain and
stiffness
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The following groups of parasitic
nematodes have two hosts (intermediate
and definitive)
– Filarioids
– Dracunculoids
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Filarioids
– Elephantiasis, heart, and eye worms
– Thin, threadlike worms that inhabit the
lymphatic system or other tissues
– Intermediate host is typically a blood sucking
insect
– Definitive host is usually a bird or mammal
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Wuchereria bancrofti
– Found mainly in Africa and Asia
– Intermediate host is a mosquito,
definitive host is a human
– Threadlike adults live in lymph glands
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Blockage of lymph vessels causes
edema
– Long term blockage causes a condition
known as elephantiasis
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Enlargement of appendages, breasts,
scrotum, etc…
– Life cycle
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Eggs hatch into microfilariae that
migrate to surface blood vessels at
night (when mosquitoes are biting)
Microfilariae migrate from mosquito gut
lumen to proboscis
Injected into definitive host
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Dirofilaria immitis
– Canine heartworm
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Loa Loa
– African eye worm
– Sometimes crosses cornea
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Dracunculus medinensis
– A dracunculoid
– Guinea worm
– Intermediate host is a FW
copepod and definitive host is
human
– Adult female lives below skin of
human and produces an ulcer
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Juveniles released in water
Ingested by a copepod
Humans ingest copepod by
drinking contaminated water
– Worms removed surgically or
by winding on a stick
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Caduceus (symbol of medical
profession) is really a
nematode curled around a stick