Transcript Lecture 13 - Some animals - Worms, arthropods and echinoderms

Lecture #11
Worms, Worms & Worms
Phylum Platyhelminthes
Phylum Nematoda
Phylum Annelida
Current Molecular Classification
• Clade Lophotrochozoa:
– Phylum Platyhelminthes - worms
– Phylum Annelida - worms
– Phylum Mollusca – clams, scallops, squids, snails
etc…
• Clade Ecdysozoa:
– Phylum Nematoda - worms
– Phylum Arthropoda – crustaceans, spiders &
insects
Phylum Platyhelminthes
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flatworms – 20,000 species
“platy” – flat
“helminth” = worm
unsegmented flatworms
novel developments (vs. Sponges and Cnidarians):
– development of bilateral symmetry and three embryonic (triploblastic) tissues in
these worms
– development of a head-like region = cephalization
– development of an excretory system = protonephridia
Phylum Platyhelminthes
• flatworms are divided into two lineages
– A. Non Parasitic
– Class Turbelleria (free-living)
– B. Parasitic:
– Class Monogenea (ectoparasitic)
– Class Trematoda (parasitic) = flukes
– Class Cestoidea (parasitic) = tapeworms
Features common to Phylum Platyhelminthes
• 1. triploblastic
– three germ layers: ectoderm, mesoderm and endoderm
– mesoderm  muscle
• 2. bilateral
• 3. flattened body plan
– thin
• 4. acoelomate
• 5. protonephridia for an excretory system
• 6. no circulatory or respiratory system
– exchange by diffusion
• 7. incomplete digestive system
– mouth, no anus
• 8. most are hermaphroditic (monoecious)
Features common to all flatworms
• protonephridia for
osmoregulation (water
balance)
• for the flatworms – influx of
water into their bodies from
their environment
• this excess water is removed
through protonephridia
• comprised of flame cells or
flame bulbs that draw the
water in and expel it back to
the outside
• free-living flatworms – e.g. Planaria &
Dugesia
• marine and freshwater
• bottom dwellers
• over 4,500 species to date
• less than 1 cm long in most species
• free-living species are shades of black, brown
and gray
• larger species can be brightly colored
https://www.youtube.com/watch?v=wn3xluIR
h1Y
Class Turbellaria
• incomplete digestive system
– most turbellarians are carnivorous and feed
on small invertebrates or scavenge dead
animals
– both extracellular and intracellular
– food enters the pharynx – enzymes secreted
into the pharnyx for extracellular digestion
– food enters the intestine where cells
phagocytose smaller food particles and
complete digestion intracellularly
Class
Turbellaria
• tubellarians have net-like nervous system (like most flatworms)
• nerve trunks that run the length of the body
– neurons organized as sensory and motor and association – seen in higher order
animals like humans
• accumulation of neurons near the head – function as a brain
• also have two auricles – have neurons for detecting chemicals
• two eyespots called ocelli at the head for detecting light
• Asexual reproduction: reproduce asexually via
transverse or longitudinal fission
Class
Turbellaria
– regenerate the missing body regions once they separate
head regeneration:
https://www.youtube.com/watch?v=kndPpqC6
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Class Trematoda
8,000 species
parasitic flatworms called flukes
wide, flat shape to oval or elongate
body plan: like the turbellarians in structure
– large intestine that splits into two tubes
– hermaphroditic
– outside is covered with an organic layer of proteins + carbohydrates =
glycocalyx
• can help evade the host’s immune system
• Flukes:
– attachment through an oral sucker that
surrounds the mouth
– a second sucker – acetebulum – located
ventrally in the middle of the body
• e.g Clonorchis sinensis – liver flukes
– infects 30 million people annually – mostly in
Asia
– adult flukes live in the human liver – definitive
host
– life cycle also requires an intermediate host –
usually a mollusc
e.g. Schistosoma – blood flukes
e.g. Paragonimus – lung fluke
e.g Clonorchis sinensis – liver
flukes
• Schistosoma – blood flukes
• adult flukes live in the human
bloodstream
• dioecious – males are shorter and thicker
• female is long and slender – carried in a
ventral canal on the male
• life cycle
– 1. copulation is continuous –
constantly mating pairs of worms
(female, smaller & thinner)
– 2. eggs are released in feces and
releases miracidia into freshwater
– 3. penetrates a snail to continue it
life cycle
– 4. larval form leave the snail and
penetrate human flesh (creates a
rash)
– 5. once in humans the larvae form
adults
Class Cestoidea
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tapeworms
3,500 species
endoparasites – vertebrate digestive system
1 mm to 25m in length
nearly all monoecious
lack a mouth and digestive tract
– absorb nutrients by diffusion
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consist of a long series of repeating units called
proglottids (repeating reproductive segments)
attachment by a scolex – holdfast that attaches the
worm to its host
live in a very stable environment – intestinal tract has
few variations
– proglottids are filled with reproductive
structures (male and female)
• devoted to making eggs
• BUT the male organs mature before the
female – no self fertilization
• fertilized eggs accumulate in the uterus
(black under the microscope)
• the further back in the tapeworm – the more
mature the proglottid and the more eggs
• the oldest proglottids filled with eggs =
gravid proglottid
• gravid proglottid breaks off from the worm
and breaks open to release the fertilized eggs
• the lost proglottid is remade up near the
neck
• beef tapeworm – Taenia saginata
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adults live in small intestine
may reach lengths of 25 meters!!
80,000 eggs per proglottid
eggs released in human feces
egg develops and forms a 6 hooked larva
called the onchosphere
– intermediate host – cattle
– onchospheres travel from the gut to the
skeletal muscle where they encyst over long
periods of time
– when eaten by humans releases the worm
into the human bloodstream – scolex
attaches to the intestine wall of the human
https://www.youtube.com/watch?v=EEBbtwG
qPEs
oncospheres
Phylum Annelida
• characteristics:
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1. segmented – into metamers
2. bilaterally symmetrical
3. coelomate
4. closed circulatory system
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large vessels that function as hearts
series of vessels closed off from the tissues
circulatory fluid = blood
gas exchange by capillary beds
– 5. complete digestive system
• mouth --> storage crop  grinding gizzard  absorptive intestine  anus
– 6. excretory system – pairs of nephridia in each segment
– 7. well developed longitudinal and circular muscles
• for locomotion = https://www.youtube.com/watch?v=0Texxu3p7I8
• excretion by nephridia
– filters body fluid
– minerals and water reclaimed
and put back into the
bloodstream
– wastes expelled to the outside
– very similar to the vertebrate
nephron
Phylum Arthropoda
• characteristics:
– 1. metamerism – segmentation PLUS specialization of body
segments for specific functions
– 2. chitinous exoskeleton for support and protection
• growth achieved through molting
• number one reason for arthropod success
– 3. paired, jointed appendages
– 4. open circulatory system & complete digestive tract
– 5. metamorphosis often seen to achieve sexual maturity
Phylum Arthropoda
• 4 subphyla
– 1. Subphylum Chelicerata
• Class Merostomata – horseshoe crabs
• Class Arachnida - spiders
• Class Pycnogonida – sea spiders
– 2. Subphylum Crustacea – 6 classes
• Class Branchipoda – brine shrimp
• Class Malacostraca – shrimp, lobsters, crab, crayfish
• Class Maxillopoda – copepods and barnacles
– 3. Subphylum Hexapoda
• insects
– 4. Subphylum Myriapoda
• millipedes and centipedes
Subphylum Chelicerata
• includes the spiders, mites, ticks,
horseshoe carbs and sea spiders
• two specialized body segments
– 1. cephalothorax – for sensory, feeding
and locomotion
• first pair of paired appendages =
chelicerae (feeding)
• second pair = pedipalps (feeding)
• followed by paired walking legs
– 2. abdomen
• contains digestive, reproductive,
excretory and respiratory organs
chelicerae
Subphylum Crustacea
• crayfish, shrimp, lobsters and crabs
• plus the copepods, fairy shrimp, isopods
(pillbugs), amphipods and barnacles
barnacle
copepod
isopod
• crayfish: known as a Decapod
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Class Malacostraca
at least ten pairs of jointed appendages
body plan: cephalothorax and abdomen
exoskeleton extends all the way around the body = carapace
abdomen takes the form of the “tail”
Decapod Appendages
• 10 pairs of appendages
used for feeding and
walking
• Head - sensory
– 1. antennae
– 2. antennules
• Thorax – feeding and
walking
– 1  3. Maxillopeds (feeding)
– 4  8. Periopods (walking legs)
• Abdomen - swimming
– 1  5. Pleopods (Swimmerets)
– 6. Uropod (part of telson)
Class Malacostraca
• feeding and digestion: prey on other invertebrates, eat plant matter and
scavenge dead and dying animals
– 1st 8 pairs of appendages are for food detection and handling
– enlargened stomach – part of which is specialized for grinding
– digestive gland called a hepatopancreatic gland - secretes digestive enzymes into the
stomach
– intestine extends from the stomach
– intestine ends in an anus – important role in water and salt regulation
• circulation: similar in all
arthropods – open system
Class Malacostraca
– tissues are bathed in body
fluids containing oxygen
binding pigments
– do have a heart
• respiratory: feathery gills
attach to the bases of the
walking appendages
– water is moved over the gills
for the exchange of gases
between the oxygenated
water and the body fluids
gills
Subphylum Hexapoda- Class Insecta
• 2 classes: Entognatha and Insecta
• insect body plan:
– body is divided into: head, thorax and abdomen
– head bears a single pair of antennae, mouthparts (maxillae,
mandibles), compound eyes and ocelli
– thorax bears three pairs of legs & wings (in some insects)
locomotion: varied
methods from crawling
to flying
Class Insecta
• feeding and digestion:
– head bears mouthparts for food
handling and sensory
• mandibles for chewing
• maxillae for cutting
– digestive tract - long, straight tube
of foregut, midgut and hindgut
The Insect Eye
ocelli
compound eye
• ocelli + several compound eyes
• ocelli = 500 – 1000 receptor cells beneath a single circular
lens
• compound eyes found in many adult insects
– better suited for detecting movement rather than for forming an
image
• compound eyes consists of a few to 28,000 receptors called
ommatidia – fuse into a multifaceted eye
• ommatidia –light-gathering structure
– covered with a cornea, contains a cone (lens)
– base is a rhabdom – converts light energy into a nerve impulse
• excretion: Malphigian tubules
– open into the junction of the midgut and hindgut
– ions, water and other critical materials are reabsorbed from the rectum
back into the body fluid
– nitrogenous wastes move into hindgut
– main excretory product - uric acid
• gas exchange : tracheae
– tubes that open to the air via the spiracles along the body
• spiracles lead to tracheal tubules that carry air to the muscles
– gas exhange
• inspiration through the thoracic spiracles and expiration
through the abdominal spiracles
Features common to Phylum
Echinodermata
• 1. triploblastic
• 2. pentaradial symmetry in adults; bilateral symmetry
in larvae
• 3. coelomate
• 4. internal endoskeleton made of calcerous (bony)
plates called ossicles
• 5. water vascular system for locomotion
Phylum Echinodermata
• approximately 7,000 species
• all are marine
• living echinoderms are classified into 6 classes
– 1. Asteroidea – sea stars
– 2. Ophiuroidea – brittle stars and basket stars
– 3. Echinodea – sea urchins and sand dollars
– 4. Holothuroidea – sea cucumbers
– 5. Crinoidea – sea lilies and feather stars
– 6. Cocnentricycloidea – sea daises
Class Asteroidea
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sea stars
about 1,500 species
live on hard substrates in marine environments
five arms radiating from a central disc
central disc has a mouth on its ventral side (oral surface)
opposite surface is the aboral surface with an anus
Water vascular system
• water-filled canals for locomotion
• water enters into a ring canal through a
stone canal and a sieve-like pore called the
madreporite
• five radial canals (or multiples) branch from
the ring canal and run down each arm
• extensions off of the radial canals are called
tube feet
madreporite
-tube feet
• extensions off the ring canals
• project to the outside & have suction
cups at its end
• inside the body they end as a bulblike,
muscular ampulla
• when the ampulla contracts- forces water
into the tube which then extends
• contraction of tube feet back into
body pulls sea star forward:
locomotion
https://www.youtube.com/wa
tch?v=2DFXGafpGkQ