Transcript Biology 320 Invertebrate Zoology Fall 2005

Biology 320
Invertebrate Zoology
Fall 2005
Chapter 13 – Phylum Annelida
Part One
Phylum Annelida
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Name means “ringed”
Mostly marine, but also
freshwater and terrestrial
representatives
Size varies greatly
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Microscopic – 3 m (giant
Australian earthworm)
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12,000 spp.
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Segmented
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Diverse modes of feeding
Body Regions
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Three main regions (anterior to
posterior)
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Prostomium
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Trunk
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Anus
Some sensory appendages
Have annulations (superficial
segments), but also true segments
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Majority of body segments
Pygidium
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Head with sensory organs
Peristomium with mouth
Internal compartmentalization
Growth zone is located just
anterior to pygidium
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Segments added posteriorly
Oldest segment is most anterior
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Some organs / structures are
found in every segment
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Other organs are parts of
integrated systems
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Appendages
Coelomic cavities
Nephridia
Gonads
Digestive system
Nervous system
Hemal system
Musculature
Segments are separated
transversely by septa
Bilateral coelomic cavities are
also partitioned longitudinally
by mesenteries
Generalized Body Wall
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Cuticle
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Protective layer that resists abrasion
and helps prevent desiccation
Annelids are still restricted to moist
environments
Epidermis
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Glandular for production of mucus
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Previously discussed functions of
mucus apply here
Produce chaetae
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Chitinous bristles that project from
epidermis
Used for traction
Not to be confused with setae of
arthropods, which are sensory hairs
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Connective tissue
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Musculature
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Circular and longitudinal
Generalized Nervous System
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CNS
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Brain is located dorsally in prostomium
Two ventral longitudinal nerve cords
with giant axons
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Impulses travel up to 40X faster than
neurons of average diameter
Facilitate the escape response
Segmental ganglia
Commissures give the nervous system a
ladder-like appearance
Sensory structures
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Typical unicellular receptors distributed
on head, body, and appendages
Polychaetes posses eyes and nuchal
organs (more later)
Coelomic Cavities
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Two lateral coelomic cavities in each segment
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Transverse septa
Two longitudinal mesenteries
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One ventral and one dorsal to gut
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Benefit is that musculature and hydrostat of
individual segments can be precisely controlled
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Coelomic cavities may be lined with
mesothelium containing chlorogogen cells
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Tissue appears yellow or brown in color
Has important metabolic functions
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Synthesis and storage of glycogen and lipids
Detoxification
Hemoglobin synthesis
Protein catabolism and formation of nitrogenous
wastes
Segmentation
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Advantages:
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Burrowing
Isolation of hydrostat and
muscular contractions
Studies have compared fluid
pressures in segmented worms
vs. non-segmented worms that
are burrowing
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Pressure is transmitted
throughout coelom in nonsegmented
In order to prevent aneurisms,
all muscles must contract in
order to antagonize pressure
Generalized Hemal System
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Dorsal and ventral blood vessel, which
are connected by capillary beds
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Blood is pumped by:
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Blood may contain some hemoglobin,
but typically larger concentrations are
contained in amoeboid coelomocytes
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Vessels
Muscular contractions
Enlarged portions of anterior dorsal
blood vessel which function as hearts
WBC + RBC hybrid
Gas exchange occurs across body
wall, appendages, and gills
Generalized Excretory System
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Paired segmental nephridia
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Funnels or terminal cells project into coelomic fluid
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Highly coiled tubule
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Large surface area for secretion and absorption
Nephridiopore opens to exterior of animal
Generalized Reproduction
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Clonal
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Fragmentation
Budding
Paratomy
Sexual
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Gonochoric
External fertilization
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Gametes exit through
nephridiopores
Gonads are segmental, and
housed in coelomic cavities
Trochophore larvae, with
growth zone just anterior
to the telotroch
Class Polychaeta
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Polychaetes or bristleworms
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Name means “many chaetae”
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8000 spp.
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Marine, a few freshwater, and a
few tropical terrestrial varieties
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Diverse feeding ecology,
locomotion, and chaetae structure
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Also abundant (13,425 / m2 in
Tampa Bay, FL)
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2 mm to 3 m (Eunice)
Body Form
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Posses appendages called
parapodia
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Lateral outgrowths of body wall
Supported by chitinous rod
Each segment bears one pair
Posses a chaetal sac which
secretes a bundle of chaetae
Chaetal structure is closely related
to lifestyle and locomotion
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Errant (motile)
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Leg shaped – crawling
Paddle shaped – swimming
Shovel shaped – digging
Sedentary
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Reduced – burrowing
Hook shaped – also for burrowing
Tubes
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Only annelids that secrete and occupy tubes
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Constructed from:
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Fibrous proteins
Foreign materials
Calcified by animal to form a shell
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Tubes may be attached to a surface or
partially buried in sediment
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Several functions:
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Protection
Hide-out from which prey can be ambushed
Brooding chamber
Sometimes tubes wash up on beaches
Nervous System
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Typical of annelids
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Segmental pedal ganglia associated with parapodia
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Sensory organs
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Nuchal organs
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Ocelli
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Best developed in errant varieties, but useful for detecting shadows in sedentary worms
Statocysts
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Unique to polychaetes
Pair of eversible ciliated chemosensory pits on prostomium
Useful to burrowers
Sensory appendages
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Antennae – prostomium
Palps – prostomium
Cirri – peristomium, parapodia, and pygidium
Digestive System
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Typical of annelids
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May have a protrusible pharynx
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With jaws for grasping prey
May be used for burrowing
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Esophageal ceca secrete digestive enzymes
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Many strategies for waste removal, based on lifestyle
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Errant – leave wastes behind while moving
Sedentary – interesting adaptations and behaviors to help avoid waste
contamination
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Some live upside down in burrows
Some invert themselves just while defecating (sensory appendages on
pygidium are useful here)
May create unidirectional water flow through the burrow tube
Nutrition
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Once again, related to lifestyle
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Errant
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Burrowers
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Deposit feeders
Sedentary (attached)
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Deposit feeders
Tube dwellers
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Carnivores often have protrusible
pharynx with jaws
Herbivores or scavengers
Suspension feed using feather crown
with large SA
Parasites
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Endoparasites of polychaetes and sea
stars
Ectoparasites that suck the blood of eels
Gas Exchange
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Body wall
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Gills
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Exposed, delicate
outgrowths of body
surface
Modified portions of
parapodia
Feeding crowns in
sedentary polychaetes,
such as feather-duster
worms, double as gills
Circulatory System
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Smaller varieties lack a hemal system, but possessed by
larger animals
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Typical annelid system plus lateral parapodial vessels
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Variety of oxygen binding pigments can be found,
especially in larger animals
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All function differently and have different oxygen affinities
Intertidal polychaetes must cope with periods of
emersion or stagnation of water
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Some undergo torpor – suppress metabolism
Rely on stored oxygen from neuroglobin or myoglobin
Excretion
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Typically have segmental nephridia
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Occasionally localized in one or a few
segments
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Feather duster worms have one pair
of anterior nephridia that empty via
one medial nephridiopore, located on
the head
Tubes are coiled to increase SA for
secretion / absorption
Osmoregulate in low salinity
(brackish) water by increasing rate of
filtration
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Removes excess water
A few species have even colonized
freshwater
Reproduction
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Clonal
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All forms of clonal reproduction
Excellent regenerators
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Chaetopterus can grow an entire
worm from one segment
Sexual
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Most only reproduce sexually
Most gonochoric
Gonads are segmental in
“abdomen”
Gametes released into coelom
Ripe gametes are shed via
nephridiopores or rupture body
wall
Epitoky
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Reproductive phenomenon
characteristic of many polychaetes
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Worms exhibit two life phases
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Atoke – benthic non-reproductive
individual, which transforms into an…
Epitoke – pelagic reproductive
individual
Epitokes arise from atokes via
metamorphosis or budding
Undergo several modifications and
essentially become swimming sacs of
gametes
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Enlargement of eyes, parapodia, and
chaetae
Become sexually mature, and
gametes ripen
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Epitokes reach sexual maturity
at the same time and swarm
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Swim to the surface and
release gametes
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Many different cues:
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Female pheromone release
Light cycles
Lunar cycles
Very predictable patters in
some
Some convert back into atokes
after spawning; some
reproduce once and die
All regulated by hormones
Oviposition
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Many shed eggs into sea
Some attach gelatinous
masses of eggs to
substrata
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Chimney of tube
Some brood eggs
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Retain eggs in tube or
burrow
Sac attached to ventral
surface of parent
Development
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Trochophore larvae in most
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Growth zone just anterior to telotroch
May pass through trochophore phase in egg before hatching
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Some direct development
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Life spans
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Some live one or two years, and reproduce once (called annuals)
Some live and breed for more than one year (perennial)
Short life spans that progress through several generations in just
one year (multiannual)
Diversity
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Lugworms
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Construct L-shaped burrows
Deposit feeders
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Arenicola
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Bamboo worms
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Construct tubes of sand that
resemble drinking straws
Deposit feeders
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Live upside down in tubes and
ingest substrate from below
Clymenella
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Paddle worms
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Paddle-like portions of
parapodia are used as gills
Errant – carnivores that
hunt prey by crawling
around
Eteone tracks prey by
following mucus trails
Ragworms
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Errant – crawl, burrow, and
swim
Eversible, muscular
pharynx with jaws
Lots of cephalic sensory
structures
Some reach 1.8 m
Nereis
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Bloodworms
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Live in shallow sedimentary
burrows
Ambush predators
Capture prey with
extremely long eversible
pharynx
Have poison glands
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Glycera
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Scaleworms
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Two rows of overlapping
scales (resemble fish
scales) on dorsal surface
Scales are actually cirri
Aphrodite (sea mouse)
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Covered with extremely
long chaetae that
resembles felt or hair
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Fireworms
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Brightly colored
Resemble caterpillars
Feed on corals and
barnacles
Calcified chaetae break off
when touched
Causes a painful, burning
sensation
Amphinome
Shaggy tube worms
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Chimneys of tubes are
ornamented with foreign
materials collected by the
worm
Camouflage for tube
Ambush predators
Diopatra
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Parchment-tube worm
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Chaetopterus
Lives in U-shaped burrow
Filter feeder
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Seines plankton with mucus net it
creates
Net is rolled into a ball and
swallowed
Mucus is bioluminescent to ward
of potential predators
Spaghetti worms
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Occupy burrows
Parapodia are reduced to grab
sides of burrow
Cluster of extensible tentacles
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Extend over sediment like active
spaghetti
Can be 1 m or more in length
Mucus on tentacles traps particles
Amphitrite
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Feather-duster worms
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Secrete calcareous tubes or
construct from foreign materials
Crown of tentacles (known as
radioles)
One radiole (most dorsal) is
modified and acts as an operculum
when crown is withdrawn
Suspension feeders
Beard worms
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Also called pogonophorans
80 spp.
Live deep in ocean; typically near
hydrothermal vents
Up to 1.5 m in length
Prostomium bears beard of
tentacles
Also live in tubes
No mouth or anus
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Symbiotic chemoautotrophic (sulfur
oxidizing) bacteria live in modified
gut (trophosome)