Download Vermes - Austin Community College

Vermes
Linnaeus – 1st to propose a formal classification of all
life on earth
 most invertebrates were lumped together
as “vermes” = worms
here we will use the term to refer to an assortment of
animals (Many different Phyla) that share a similar
wormlike body plan
Some Worm Characteristics
1. elongate cylindrical body
usually with head and sense organs at one end
2. all are invertebrate animals
(doesn’t include snakes, eels, etc)
3. body plan more complex than in the “simple
animals” described earlier
most have all 4 major kinds of animal tissues
most have well developed organ systems
including:
nervous system
with simple ganglia for brain and double nerve cord
digestive system
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complete digestive tract with mouth at one
end and anus at the other
excretory system
reproductive system
many with respiratory systems
5. most move using a hydrostatic skeleton
 hollow body filled with fluid surrounded by
muscle layers in body wall
some glide on slime trails
many different unrelated animal groups have these
characteristics in common:
Planarians (Platyhelminthes)
Ribbon Worms (Nemertea)
Gastrotrichs (Gastrotricha)
Thread Worms (Nematoda)
Horsehair Worms (Nematomorpha)
Sand Worms (Polychaetes)
Earth Worms (Oligochaetes)
Velvet Worms (Onycophora)
Peanut Worms (Sipuncula)
Spoon Worms (Echiura)
Beard Worms (Pogonophora)
Priapulids (Priapulida)
Horseshoe Worms (Phoronida)
Arrow Worms (Chaetognatha)
Acorn Worms (Hemichordata)
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Planarians
body is elongated, slender or leaf-like or long and
ribbon-like
 still rely on diffusion for much exchange of
gasses, nutrients and wastes
range in size from fraction of an inch to almost
1’ long
often brightly colored
some marine forms have warning coloration
poorly known in fossil record but possible trails have
been found from 565MY
may be first animal to have a head & tail
may be first animal to have bilateral symmetry
may be first animal to show directed movement
mostly bottom dwelling aquatic forms
mostly freshwater
some are marine
a few are even terrestrial (6 sp in US)
have true organs
each made of several different tissue layers
sponges have various specialized cells but no true
tissues or organs
jellyfish and corals have 2 tissue layers and a
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few simple organs
have distinct head with concentration of sense
organs
pair of brainlike ganglia
no rigid skeleton for muscles to act on
two layers around body
circular muscle
longitudinal muscle
epidermis is ciliated
secretes mucous trail and uses cilia to glide on it
land planarians can glide ~6’/hr
Feeding & Digestion
are mainly carnivores
some are scavengers
feed on small crustacea, nematodes, rotifers,
insects
mouth at the end of a muscular “prehensile”
throatlike tube
= pharynx
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is NOT at front of animal
some have more than one mouth & more than one
pharynx
can detect food at a distance by chemoreceptors
entangle their prey in mucous
wraps its body around prey
secretes enzymes to help “predigest” prey
sucks up bits of prey
incomplete digestive tract in most
mouth, no anus
in intestine secrete enzymes which further digest prey
in some planarians digestive tract is highly
branched to distribute food throughout the animal
undigested food is egested through mouth
Excretion
some have very simple respiratory system to remove
some some wastes
 in most takes form of “flame cells”
cupshaped area with tuft of flagella
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beat of flagella resemble candle flame under
microscope
wastes and excess water diffuse into bulb
flagella create current to send wastes through tube
which opens to outside of the body
Nervous System
planarians were probably the first creatures to
have a brain
but a few primitive members have nerve net like cnidarians
have pair of ventral nerve cords
connected by ladder like interconnections
head with simple brain-like ganglia
head with sense organs:
no eyes (=ocelli), 2 eyes or 100’s of eyes
can’t form images, only detect light
auricles for touch and chemical senses
Reproduction
many reproduce both sexually and asexually
Asexual:
a. Regeneration
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turbellarians have considerable powers of
regeneration
eg. slicing and dicing experiments
replacement of lost parts
also to recover from long food shortage
can survive for months by self
digesting up to 90% of their body
regenerated worms may be able to retain
learning:
taught planarian to run a maze
cut in half and allowed to regenerate
both new worms learned the maze quicker
early researchers also reported learning by cannibalism
 but has never been repeated???
b. Fragmentation
when alarmed they can break up into dozens
of “blobs of slime”
in a few hours each piece will become a new
worm
c. Fission
pinch in half
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some times produces a chain of zooids
 superficial resemblance to segmentation
Sexual:
most are monoecious (hermaphrodites)
during breeding season each individual develops
both male and female organs
cross fertilization not self fertilization
some with internal fertilization
some with vaginas & penises
usually open through common genital pore
mating ritual resembles a fight
each trying to get penis in genital pore of the other
or sometimes just impales the other
some without vagina use “hypodermic
impregnation”
fertilized egg is enclosed in coccoon which is attached
by stalks to underside of stones or plants
some marine species produce ciliated larva
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Ribbon Worms
(Phylum Nemertea)
~1000 species
slender, very fragile ribbonlike worms
often very brightly colored
some white, red, yellow, green, purple
most ~8” (<20 cm) but longest animal in existence is a
nemertean = 180’ (60 M) long
regardless of length most are <1”
(23mm)
wide
almost all are marine
found in every ocean; from surface to abyssal
zone
most are benthic; a few pelagic species
fairly common on beaches; often inside dead
shells
 resemble tangled mass of slimy string
arctic ribbon worms commonly wash ashore by the
billions
a few are found in moist soil or freshwaters
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(eg. Prosoma is common in fw ponds)
they build slime houses
they can tie themselves into inextricable knots
or curl up into balls and secrete a covering of
mucus around themselves
general body plan similar to planarians
Feeding
carnivores
eat earthworms, sea worms, small mollusks and any
small soft bodied animal
use eversible proboscis to stab prey
often at front of proboscis is sharp pointed spear-like
stylet that impales prey
often tipped with poison
“Nemertea” translates as “unerring one”
 refers to animals ability to very accurately shoot its long
proboscis to capture prey
sometimes impales with such force that it breaks
off
writhes for hours
animal can grow a new one
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in some the proboscis is a sticky lasso that coils
around its prey
proboscis (pharynx) is unusual because it is not
connected to digestive tract in most
ribbon worms have complete digestive tract with
anus
 one way path from mouth to anus
like snakes they can devour animals larger than
themselves
without food some can live up to 1 yr by self digesting
like planarians
most can shrink at will to < 1/3 their ordinary length
Circulatory System
true blood vascular system
Reproduction
Asexual
a. some reproduce asexually by fragmentation
some can break into 100’s of fragments
each fragment can grow into a complete worm
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b. regeneration
some with great powers of regeneration like
planarians
Sexual
most are dioecious (unlike flatworms)
fertilized egg develops into ciliated larva
some fragment in warm weather and reproduce
sexually in colder weather
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Horsehair Worms
(Phylum Nematomorpha)
326 species; probably many more
also called “hairsnakes” or “hairworms”
worldwide distribution
abundant in aquatic and moist environments
free living as adults and parasitic as larvae
adults mostly ~ 4”
long,
(~10 cm);
very slender <0.1” dia
range up to 3’ (100cm)
(1-3mm)
reddish or dark brown
really do resemble the hair of a horses tail
found in puddles after rain usually contorted into knots
(also called gordion worms)
in all types of freshwater habitats with good oxygen
levels
in old days were common in horse troughs
once thought they were literally produced from horses hairs
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in days past:
every summer kids would pull hairs out of
horses tail and place them in a jar of water
put on window ledge in the sun
watched and waited to see the “transformation”
skin covered by cuticle
secreted by epidermis
adult does not feed
has complete but degenerate digestive system
but can absorb some nutrients through body wall
simple nervous system with ganglia and nerve cord
extending down trunk
some have eyespot on head
no circulatory, respiratory or excretory system
Reproduction & Development
dioecious  distinguished by caudal end:
gametes released through anus
copulation in many species
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male and female become tightly intertwined
eggs laid on vegetation in water
in long strands
hatch into larva with spiny proboscis
larval stages are all parasitic in many kinds of
insects, esp grasshoppers, myriopods, crustaceans
some bore into host; others are eaten by host
then hatch out
larvae absorb nutrients from host’s body cavity
parasites stimulates host to seek water
adults emerge only when host is in water
adult then quickly become sexually active
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Threadworms
(Phylum Nematoda)
= eel worms; round worms
~25,000 species;
specialists estimate up to 500,000 sp
a few fossils known; some in amber
very common and diverse group but poorly known and
difficult to identify
very simple and highly adaptable design:
long, threadlike cylindrical shape with few
distinctive features visible
difficult at first glance even to distinguish front from back
end
most are very small 100th of an inch to 1/5th inch
(0.5-1.0mm)
live in almost every habitat from arctic to tropics:
ocean, hot springs, lakes, ponds, damp soil
probably the most abundant animal on earth
especially common in soil
as numerous in soil as are arthropods
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eg. est 6 M individuals in 1 ft3 of soil
eg. upper 1” of rich soil may contain >1 Bill/acre
 virtually every soil sample will yield new
species
the animals discussed so far lacked any kind of body
cavity
 organs when present were embedded in jelly-like secretion or
simple tissue
virtually all other major animal phyla have some kind
of body cavity
‘tube within a tube’ body plan:
 allows an increase in size
 allows more elaborate lengthening and coiling of internal
organs
 allows circulation of gasses, food and wastes in the
absence of a circulatory system
 provides hydrostatic skeleton
Body Wall
secretes tough but flexible cuticle
 protects worms from abrasion in soil and
sediment
some have an elaborately sculpted cuticle
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Movement
unlike most wormlike animals they have only
longitudinal muscle in body wall
hydrostatic pressure in fluid filled body cavity
maintains internal pressure and keeps body wall
from collapsing
body wall with a single layer of longitudinal muscles
only
 produces whiplike or snake-like thrashing
motion
Feeding and Digestion
all nematodes eat living cells
eg. bacteria, fungi, plant & animal
some are predators on unicellular life
(many are also parasites)
mouth is at front end of muscular pharynx
leads to complete digestive tract and exits through
anus near posterior end
no muscles lining intestine - collapsed thin tube
Nervous System
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dorsal and ventral nerve cords
controls dorsal and ventral muscle layers
“brain” = nerve ring with ganglia around pharynx
Senses
especially chemoreceptors
sometimes in head; or tail
Excretory System
simple excretory system a series of canals
or similar to planarians
no circulatory or respiratory system
body fluids circulate nutrients, oxygen and wastes
Reproduction
usually dioecious with sexual dimorphism
 males distinct from females
amoeboid sperm (no flagella)
young go through several “juvenile” stages with molt
at end of each one
some can enter a state of arrested activity
= cryptobiosis
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 makes them successful in seemingly
unfavorable environments
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Sand Worms
(Phylum Annelida; Class Polychaeta)
sand worms, bristle worms, fan worms, clam worms,
etc
10,000 species; 2/3rds of all species in phylum
mostly marine
most 2-4” long
(5-10 cm)
; some up to 10’
(3 M)
often brightly colored
live in crevasses, old shells, burrows
some live in tubes they secrete or make with sand or
shell
deposit feeders, filter feeders, predators, scavengers,
some have elaborate filtering structures
eg feather dusters
a few are planktonic
important in marine food chains
Body Form
most long and wormlike
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some with bizarre forms
well developed segmentation
seen in just a few other phyla: eg arthropods, chordates
segments are separated by tissue = septae
allows more efficient hydrostatic skeleton
offers a way to achieve greater size:
rather than increasing size of each organ; each organ is
repeated in each segment
most have chitinous bristles = setae repeated on
each segment (ie. “bristle worms”)
used as anchors while burrowing or to prevent
capture
some used for swimming
or as protection or camoflage
most have a distinct head
with pharynx and chitinous jaws
tentacles palps and sensory structures
most have paired appendages on most segments
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= parapodia
used for locomotion
respiration
in some, parapodia modified into fans and mucous
bags for feeding or to create water currents
Movement
body cavity is filled with fluid which serves
as hydrostatic skeleton
can also use parapodia alternately to crawl
across surface or as fins to swim
Feeding & Digestion
free swimming polychaetes are mostly predators
some with eversible pharynx with jaws
in others the pharynx produces a suction to draw
food into mouth
sedentary polychaetes are filter feeders or deposit
feeders
complete digestive tract “tube within a tube” design
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muscle layers surround tract and allow modification of
tract into various structures:
crop: food storage area
gizzard: thick and muscular; helps physically break up food
intestine: in some the first part of intestine is used for
digestion; secretes digestive enzymes
Respiration
usually through parapodia
some have paired gills on some segments
Circulation
double transport system for foods, gasses, wastes
fluid filled coelom
also circulatory system with heart & vessels and
blood
several pairs of aortic arches (=”hearts”) help to
keep pressure up in ventral vessel
foods, wastes and respiratory gasses are carried both
in blood and in body fluid
Nervous System
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brain a pair of cerebral ganglia
paired ventral nerve cords
with pair of ganglia in each segment
ladderlike connections in each segment
Senses:
eyespots
eyes with retina and rod-like receptors
a few polychaete eyes have cornea, lens, retina
 can form images
statocysts in some
tentacles & palps  touch
other simple chemoreceptors
Excretion
more elaborate excretory system than previous
animals discussed
excretory organs also help in salt and water balance
Reproduction & Development
most are dioecious
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simple reproductive system
have no permanent gonads
 gonads appear as temporary swelling of
peritoneum at certain seasons
gametes are shed either
 through genital ducts
 or through nephridiopore
 or through rupture in body wall
some sand worms live most of the year as sexually
immature individuals
after living 1 or 2 years as benthic organisms they
become sexually mature and swollen with gametes
head shrinks, body enlarges, gonads develop and
produce egg or sperm
sometimes only part of the body makes the transformation,
breaks off and the rest of the worm lives to repeat
next season
eg. palolo worm
males and females gather by the millions in one spot
at night determined by phases of the moon
female releases pheromone
pheromone excites male to circle about female
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swarms of epitokes appear at start of moon’s last quarter in
oct or nov
 sea is literally thick with epitokes
just before sun rises, epitokes burst to release gametes
anterior portion of worm returns to burrows
=synchronous mating
ensure most eggs are fertilized
predator saturation
predators have a field day; but too many prey so
some are always left to reproduce
atokes safely in their burrows to repeat next year
a Samoan holiday to feast on epitokes
Ecological and Economic Impacts
eg. detritus food chains
eg. prominent in marine food webs
eg. human food (samoa)
eg. beardworms are base of entire ecosystem not
based on photosynthesis
discovered in 1900; today 150 known species
most live in deep ocean
common in hydrothermal vent communities
no digestive tract
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they get most of their nutrients from symbiotic bacteria living in
an organ (=trophosome) within the trunk of the worm
bacteria harvest energy from H2S and convert inorganic
elements into sugars for the worm
CO2 + H2S + O2 + H2O  H2SO4 + sugars
have well developed circulatory system containing
hemoglobin
use hemoglobin to carry oxygen to body cells and to
carry oxygen and hydrogen sulfide to bacteria
eg. Major decomposers of deep sea whale carcasses
2001 found red fuzz on whale carcasses in deep ocean
1000’s of polychaetes with red plumes up to 6 cm long
new genus and species of polychaete
seem to be unique to “whale fall”
worms have no functional mouth or gut
have symbiotic bacteria that digested oil in bones
 they degrade hydrocarbons
the bacteria live in rootlike structures of worm that extend in and
throughout the bone
worm provides oxygen via blood vessels extending into the roots
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Earthworms
(Phylum Annelida; Class Oligochaeta)
means “few setae”
over 3000 species
mostly terrestrial; most abundant ‘worms’ on land
burrow in the soil
most are less than ~1’
(30 cm)
some tropical earthworms get up to 9’
(3 M)
long
relatives of sand worms but no parapodia
and very few setae
no distinct head
earthworms have no “eyes” but do have numerous
photoreceptors in epidermis
Feeding & Digestion
most are detritus feeders and scavengers on decaying
organic matter
well developed digestive tract:
mouth pharynxesophagusgizzardintestine anus
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pharynx - pumps food in
crop - temporarily stores food
gizzard - muscular, lined with cuticle, grinds food
intestine - most chemical digestion and absorption
allows them to eat soil and then the intestine sorts
out the nutrients for absorption
eat as they burrow then let digestive system
extract nutrients
eg. Night Crawler
burrow within the upper 30 cm of moist soil rich in organic
matter
mainly active at night
on warm damp nights, forage for leaves and organic
debris
up to 54,000 earthworms /acre
 turn over 18 tons of soil per year
prefer moist soil but if too much water they will move to
surface
 sometimes in great numbers
 used to think they “rained” down from the sky
important in keeping soil fertile since they are
constantly turning over earth and mixing
organic matter into it
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if all material ever moved through earthworm gut was
piled on surface of earth it would rise 30 miles
above sea level (5x’s height of Mt Everest)
Respiration
no respiratiory organs or parapodia like polychaetes
breath through skin, no lungs or gills
extensive system of capillaries beneath cuticle
Circulation
have circulatory system with 5 pairs of hearts
and hemoglobin in blood to carry oxygen
Excretion
main excretory organs are nephridia
in each body segment
Nervous System
same as sand worms
Sense Organs
distributed all over body
photoreceptors
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chemoreceptors
many free nerve endings  probably tactile
Earthworm Reproduction
earthworms are hermaphrodites
cross fertilize each other
copulation involves a double exchange of
sperm cells
mucous secreted from clitellum holds pair
together with genital pores aligned
can last 2-3 hours
sperm is deposited in seminal receptacle
after copulation worms return to burrows
fertilization and egg laying occur a few days later
each worm secretes a sheath of mucous around
clitellum
clitellum then secretes nourishment for egg
then envelopes mucous and food in tough
chitin-like cocoon
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the worm then backs out of the cocoon
as cocoon slips over the genital openings it
receives an egg, then sperm
fertilization occurs in the cocoon
cocoon is deposited in soil
in 2-3 weeks a new worm emerges
Ecological and Economic Impacts
detritus food chain
food for birds and other animals
bait
soil fertility
important in keeping soil fertile since they are
constantly turning over earth and mixing
organic matter into it
if all material ever moved through earthworm gut was piled
on surface of earth it would rise 30 miles above sea
level (5x’s height of Mt Everest)
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Velvet Worms
(Phylum Onycophora)
70 species
closely related to arthropods
an ancient phylum
 has changed little since the Cambrian (500MY)
cylindrical segmented body 0.5-6” (1.4-15 cm) long
blue, green, orange or black
originally a marine animal (Burgess Shale)
today all are terrestrial
found in rainforests and semitropical habitats
mostly nocturnal
tend to avoid light
Body Form
long cylindrical segmented, wormlike body
entire body is covered by bumps (=tubercles) which
are covered by tiny scales
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 giving the body a velvet appearance
have 14-23 pairs of legs
each leg has a pair of claws
looks like slugs with legs
thought to be a mollusc when first discovered in 1826
anterior end with pair of antennae and ventral
mouth
believed to be a phylum closely related to arthropods
Movement
fluid filled body cavity is used as hydrostatic
skeleton
crawls slowly on peglike legs
Feeding & Digestion
well developed digestive system
mouth with a pair of claw like mandibles
most species are predaceous
feed on snails insects and worms
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have slime glands that shoot milky fluid that quickly
congeals into slime
can shoot slime up to 30”
once captured they secrete enzymes (salivary
secretions) into prey to partially digest it before
eating
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