Lecture 3 RH Flashcards
What are the 3 phyla of worms?
Platyhelminthes
Nematodes
Annelids
Are worms coelomates?
Different phyla have different properties when it comes to the body cavity:
Platyhelminthes are acoelomate
Nematodes are blastocoelomates
Annelids are normal coelomates
How are the coelomes of the different phyla of worms different?
Coelomates have mesoderm derived tissue lining the coelom all around the body cavity and the organs.
Blastocoelomates coeloms are lined by mesoderm tissue only on the outside of the cavity.
What is a feature that is common to all worm phyla regarding their embryonic development?
All worms develop from 3 embryonic layers and are tripoblastic.
What do platyhelminthes look like?
They are flat and long.
Many are parasitic.
What are the key features of platyhelminthes?
Triploblastic
Acoelomate
Bilaterally symmetrical
Blind gut or not gut
Unsegmented
Flat
Cellular filling between epidermis and gastrodermis is the parenchyma
Muscles: Longitudinal, circular, dorso-ventral, oblique
No circulatory or gas exchange system
Excretory system: Protonephrida
Hermaphroditic
What is the cellular filling in platyhelminthes between the epidermis and the gastrodermis called?
Parenchyma
What is the musculature of platyhelminthes like?
They contain longitudinal muscles that form a ring around the animal and run all the way anteroposteriorly
Circular muscles form a ring around the body cavity
Parenchymal muscles run dorsoventrally
Are platyhelminthes ciliated?
Yes, they use it to glide across a surface
Why can platyhelminthes grow to such massive lengths?
Their flat body structure creates a high surface area which allows more easy gas exchange and nutrient exchange with environment.
How do platyheminthes regulate osmolarity?
They use protonephridia
How do platyhelminthes osmoregulate?
Tubules run from parenchyma to pores on outside of the body used and if you expand one of those you would see excretory duct/nephridiapore. the rest of the tubule is buried in the parenchyma and contains flame cells at the end of it to draw water through it and down through the tubule. This structure contains cilia which allows liquid movement.
Some of this fluid can be reabsorbed by the worm in the excretory duct to form more concentrated excretion.
What are the classes of platyhelminthes?
Turbellaria
Monogenea
Trematoda
Cetoda
What kind of grouping is class turbellaria?
Paraphyletic grouping
What are the key features of class turbellaria?
They are not parasitic
Very diverse and capable of living in many habitats (marine, freshwater, and terrestrial)
Well developed brain with ganglia
Cephalised (complex nervous system and sensory organs such as statocysts, ocelli, chemo and mechanoreceptors)
What are the kinds of sensory receptors that turbellaria contain?
Statocysts (balance receptors)
Ocelli (simple photoreceptors)
Chemoreceptors
Mechanoreceptors
What does the gut of the platyhelminth look like?
Very branched with a pharynx that leads to it posteriorly.
What are the methods of locomotion of turbellarians?
Ciliary gliding (use mucous and cilia to glide)
Pedal waves (moves side of body in waves which moves it forwards)
Looping by moving the entire body from heel to head and “roll” with temporary attachments.
How do turbellarians temporarily attach to the substratum?
Using suckers
Using mucus and adhesive cilia
Using Duo gland adhesive system.
How does the duo-gland adhesive system work in platyhelminthes?
Viscid glands release sticky mucus and releasing gland liquefies the mucus to release.
What is the function of turbellarian rhabdites?
Capsules released into epidermis from parenchyma and they absorb water and expand and create mucus.
These cells are also important for defending the cells and recognizing chemical threats.
How do turbellarians reproduce?
They are hermaphrodites. The stylet penis pierces mate’s body wall and injects sperm.
What larva is formed in turbellarians?
Muller’s larva
What are the common adaptations of the parasitic classes of platyhelminthes?
Uncephalized, reduced nervous system, fewer sensory organs
Loss of feeding structures or gut
Loss of ventral locomotory cillia
Attachment organs or hooked mouthparts
Sucking mouthparts
Syncytial tegument
Avoidance of host immune system
Facultative anaerobes
Hermaphroditism
Complex life cycles (including asexual preproductive stages)
High rate of reproduction
Multiple hosts
Motile or encysted stages that transfer to new host
Alter behavior of host to promote successful transmission
What is the syncytial tegument?
Replaces ciliated epidermis and this is a joining of cells within the parenchyma to the outer zone of the neodermis in a way that the cytoplasm of these cells is continuous with this zone.
As a result this layer is multinucleated and as a result has immune evading capabilities.
What are the parasitic classes of platyhelminthes?
Monogenea (ectoparasites)
Trematoda (endoparasites/flukes)
Cestoda (endoparasites, tapeworms)
What types of hooks are characteristic of class monogenea?
Opisthaptor
What defines monogenea?
Platyhelminthes that live on a single host and are ectoparasites
What are the components of the anterior mouth of the trematodes?
Oral sucker at one end and a muscular pharynx at another
What are the hosts that liver flukes have?
Snail
fish
Human
What is the life cycle of the liver fluke?
1) Adults undergo Sexual reproduction releasing fertilized eggs in human faecies
2) Egg contains miracidium which hatches after being eaten by a snail or burrow into snail’s body
3) Miracidium undergo asexual reproduction in the snail creating sporocysts and redia in massive numbers.
4) Redia form Cercaria which swim through the water habitat to enter fish.
5) Humans eat fish reintroducing more liver flukes into the new life cycle.
What is a miracidium?
larval stage of the liver fluke
What do redia do?
They form cercaria which can infect fish
What does the liver fluke do to people with celiac’s disease?
It reduces the symptoms
What are the features of tapeworms?
No digestive system and other body organs. Instead they directly absorb nutrients via their cell membranes
What are proglottids?
Proglottids are segments of cetodes (tapeworms). Each segment contains a separate reproductive system.
What is the lifecycle of beef tapeworm like?
Human feces contains proglottid -> grass contains larva (oncosphere) -> Grass ingested by cow -> Cysts form in muscle of cows -> human eats rare beef getting tapeworm
Are tapeworms specific with their host?
No
What are potential complications of tapeworms?
They can form a hydated cysts which can travel in the systemic circulation and has tumour-like symptoms
What are the features of nematodes?
Thread-like appearance
more than 25000 species in every form of habitat
Most are microscopic but parasites can often get to macroscopic sizes
Extremely abundant in their habitats
Blastocoelomates
Triploblastic
Bilaterally symmetrical
Protostome
Complete gut
Unsegmented
What is the difference between a blastocoelom and a normal coelom?
Blastocoelom contains mesodermally derived tissue around the cavity (like parietal peritoneum and no visceral peritoneum)
Coelom contains mesodermally derived tissue around organs and the full cavity
What makes up the nematode anatomy?
Collagen cuticle with crossed fibers preventing deformation.
Cuticle is molted 4 times during lifetime.
Longitudinal muscles in 4 bands, but no circular muscles; no peristalsis just writhing motion
Some species have syncytial epidermis
No locomotor or feeding cilia
Brain, dorsal, and ventral nerve cords
Chemosensory organs: Amphids anterior, phasmids posterior
No circulatory or gas exchange system.
Excretion by renette cells
Dioecious, internal fertilization; free-living worms have no larvae, parasites variable.
Eutly: constant number in adults
What are amphids?
anterior chemosensory organs in nematodes
What are phasmids?
Posterior chemosensory organs in nematodes
What are renette cells?
Excretory cells in nematodes
What are the characteristics of nematode reproduction?
They are dioecious, fertilization happens internally.
Do nematodes produce larvae?
Free-living don’t produce larvae
Parasitic nematodes are variable
What are defining characteristics of nematodes?
Their chemosensory organs
What does Eutely mean?
Cell division stops at maturity and so there is a constant cell number in adults
What is the hookworm life cycle like?
Embryos exit in human feces -> larvae emerge in soil -> larvae penetrate circulatory system through feet -> carried into heart then lungs -> migrate from lungs to pharynx and is swallowed -> goes through GIT to intestines
What do filarial nematodes do?
Block organs or circulatory system
Intermediate host is blood sucking insect (eg mosquito)
*examples of these worms include heartworm and elephantiasis
What are the key features of phylum annelida?
Segmented
Coelomate
Protostome
Triploblastic
Complete gut
Chitinous setae in epidermis used for traction
Have a brain, ventral nerve cord, and metameric ganglia
Closed circulatory system
Metanephridia for excretion
What are the annelid classes?
Polychaeta
Oligochaeta
hirudinea
*these are old classifications that are currently under review
What are the advantages of having a coelom?
Can act as a hydrostatic skeleton
Cushioning for the digestive tract
Muscular movements of digestive tract isolated from outer body wall and skeletal muscular movements
Coelom can function in circulation, waste removal, gamete storage, and gamete release
What is metameric segmentation?
Body is divided into segments with serially repeating organ systems.
Serial homology; homologous segments arranged in linear order
What is serial homology?
All segments arised from the same body plan and developmental origin
What are the advantages of metameric segmentation?
Improved locomotion efficiency using hydrostatic skeleton
Independent nervous control and movement of segments
Architectural redundancy allows specialisation of segments as well as survival/regeneration when segments are lost.
How does peristaltic motion work?
1) Circular muscles contract creating longer and thinner segments
2) Forward segments form an anchor when longitudinal muscles contract and fatten them.
3) The longitudinal muscles bring the entire body of the worm forwards
How does the metanephridium?
Opens on one end to the segment before it and opens on the other end to the outside via nephridiopore
What are the features of the polychaete class?
Mostly marine
Paradopia (contain fleshy lobes that are not jointed)
Numerous setae
Diverse anterior appendages
Some appendages can function as gills, or gas exchange across parapodia.
Diverse locomotion, feeding modes, ecological niches.
Trochopore larvae
What are parapodia?
Fleshy lobes found in polychaetae. Setae protrude from these parapodia.
These increase surface area significantly
What is a trochophore larva?
The larvae of annelids with bands of cilia around them.
They have a complete gut but no coelom
What is the cycle that benthic aquatic invertebrates usually follow during their life?
Most benthic aquatic invertebrates have a planktonic larval stage that disperses.
Adult stage associated with substratum
Larvae respond to various cues from physical and biological environment when selecting settlement site
How do larvae choose where they settle on the substratum?
Cues are used by larvae to know whether they want to settle down on a surface or not. Some larvae react positively while others react negatively
How do polychaete feed?
Suspension feeding: Capture food from water via tentacles which contain cilia.
Deposit feeding: Feed on material that falls to the bottom of the water using their tentacles.
Are polychaete’s mobile?
Some are, some are not
What can the eversible pharynx be used for and how?
Scavenging
Predation
Deposit feeding
What is the function of the eversible pharynx?
picks up particles from around by extending the pharynx
How do modified parapodia assist in filter feeding?
Water moves through a hollow tube which leads to the mouth and food gets caught in a mucous net and is directed to a food cup.
What are the features of siboglonid polychaetes?
No mouth, gut, or anus
Digest symbiotic chemosynthetic bacteria that grow in specialised organ (triphostome), deriving energy from reduced chemicals in the environment.
What are the features of class oligochaeta?
Mostly terrestrial or fresh water burrowers
No parapodia, few setae, reduced head appendages
Hermaphroditic
Clitellum secretes mucous cocoon for eggs and sperm
Direct development (no larval stage)
How do earthworms reproduce?
1) 2 worms come next to each other and fill up with sperm from each other at the sperm receptacle.
2) Eggs deposit in mucous sac
3) Fertilization
4) Cocoon slips off and forms another individual (no larval stage)
Which classes share the clitellum? What is the clittelum?
Clitellum is an important organ for fertilization to take place and to eventually form a cocoon.
Oligochaeta and hirudinea share the clitellum.
What are the features of hirudinea?
Mostly freshwater predators or ectoparasites
No paradopia, setae, or internal septa
Fixed number of segments (usually 34), external secondary annulation
3 jaws with teeth
Parasites have anterior and posterior suckers
Clitellum evident only during breeding season
Mostly direct development
What is external secondary annulation?
False rings externally
What do leeches inject when biting?
Anticoagulant (hirudin)
Vasodilator
Anaesthetic
What does the muscular pharynx do in leeches?
Pumps blood
How are hirudo medicinalis (leech) teeth arranged?
3 Y-shaped blade-like jaws make efficient cut that takes long time to heal
What is the problem with current class classification of Polychaetes and oligochaetes?
They are paraphyletic and undergoing changes
