Lecture 16 Invertebrates 3: Cnidarians and Plathyhelminthes Flashcards
Coelom is
internal, fluid filled body cavity that is lined with mesoderm = a place for nutrient and oxygen exchange and place where internal organs can move independently of each other, may act as hydrostatic skeleton.
Protostome is
the mouth appears before the anus during development, and the coelom forms as a splitting of the mesoderm.
Deuterostome is
the first opening (the blastopore) becomes the anus and the mesoderm and the coelom forms from outgrows of the primitive gut
Cnidaria phylum described as
- Diploblastic, radial symmetry, blind gut
- jellyfish, sea anemones, corals, hydrozoans
- ~11,000 species
– mostly marine
– found in all oceans, occupying habitats from surface waters to bantic substrates
– microscopic to many meters long - Diploblastic
- Simple nervous (no ganglia or brain, just a net of nerves) and muscular tissue
Body plan of a Cnidarian
One opening used for both ingestion of food and elimination of waste
Mesoglea with collagens give it transparent appearance
Opening of gut upwards–polyp (sessile)
ex. sea anemone
Opening of gut downwards–medusa (motile)
ex. jellyfish
Sessile polyp has a trunk with oral disk with tentacles surrounded by a central mouth
Medusa free floating.
Both polyp and medusa are capable of movement via contractive muscle like cells
Most life cycles include both body plans
Exceptions: Sea anemones, corals (no Medusa, polyps produce sexual gametes)
How do Cnidarians obtain energy
Key feature: cnidocytes - - Specialized cell used for capturing prey
- Located near mouth or in tentacles
When cnidocytes sense a prey, eject nematocyst (with barb and toxins).
Four groups under Cnidarians
- Hydrozoa
- Scyphozoa (the true jellyfish)
- Cubozoa (box jellyfish)
- Anthozoa (true corals, anemones, sea pens)–“flower animals”
Describe Hydrozoa (Hydra and Portuguese man-of-war)
Hydra
* freshwater
* no medusa stage
* moves by gliding, somersaulting or floating
* Bubble at basal disk allows floating, release bubble to sink
* 2-5 mm
Portuguese man-of-war
* tropical, subtropical oceans
* colonial polyps specialized for different functions (gonozooids-reproduction; gastrozooids; dactylozooids-catching prey)
* gas-filled float: pneumatophore (a polyp)
* tentacles contain cnidocytes
* up to 50 m long tentacles
Nervous system of Hydrozoans
- Simple nerve net
- No integration of signal
- Sensory information can come in from any direction
Note: organisms with radial symmetry are equally likely to encounter prey or environmental cues from any direction
Life cycle of Hydrozoan Obelia
Obelia: genus, mostly marine.
Colonies attached to hard surface or seaweed
Describe Scyphozoa and its example Cassiopeia
True jellyfish
* ~200 species
* large amount of mesoglea
* typical bell shape, arms around the mouth, tentacles and sensors at edge of bell
* oral arms have some nematocysts strong enough to be felt by humans
* prey on fish larvae and zooplankton
* important food for leatherback turtles
ex:
Cassiopeia
* lies on bottom in shallow waters
* “upside down jelly”
* mouth reduced
* symbiotic algae and dinoflagellates in tentacles
* Gets O2 and nutrients from symbionts;
* lives in mangrove swamps
Describe Cubozoa “box jellyfish”
Cube shaped Medusa form
Some species contain potent toxins
Found in tropical and subtropical waters, posing serious danger to swimmers
Describe Anthozoa–“flower animal”, and examples: sea anemones, corals
- Larvae directly into polyp
Sea anemones
* retract tentacles in defense
* tentacles have cnidocytes
* Predatory animals
* mutualistic relationships (+/+) with particular species of fish and shrimp. ex: Clown fish dances with sea anemone for reisdence, and secretes a layer of mucus on skin, immune to sting. Safety and food scraps – drives off intruders and removes parasites
Corals
* form colonies of myriad of genetically identical polyps;
* secrete calcium carbonate to form hard skeletons that become the framework of coral reefs.
* mutualistic (+/+) relationship with dinoflagellates, (zooxanthellae): protection, pigments – nutrients, O2, remove waste. Thus reef corals require clear water for photosynthesis
Explain “Coral Bleaching”
- Serious recent ecological problem
- Zooxanthellae expelled, change in color of coral
- Stress response due to a variety of factors:
- inc. water temp; inc. UV radiation; pollution; disease (bacteria)
Importance of coral reefs
- reefs shelter 25% of marine species
- Protect shorelines
- Support fisheries
- Tourist attraction
- Medical discovery
Three different body plans with respect to body cavities in triplobast animals
Key innovations: as hydrostatic skeleton, circulation of oxygen, nutrients, protection of internal organs.
Humans have two coelomic cavities (thoracic and abdominal)
1. Coelomate (Eucoelomate): coelom = cavity - only in contact with mesoderm
2. Pseudocoelomate: false coelom - in contact with mesoderm and endoderm
3. Acoelomate: no body cavity
Describe coelomate
- mesoderm lines the entire cavity as a “peritoneum”
Annelids, Mollusks, Arthropods, Echinoderms, Chordates. Found in most triproblasts
Describe pseudocoelomate
- “false coelom”
- mesoderm lines the outside of pseudocoel
- ex: Nematoda, Rotifera
Describe acoelomate
- no body cavity
- solid except digestive space
- flatworms lost their coeloms
Describe two ways to make a coelom
- Schizocoely
* splitting within the mesoderm
* Called protostomes - Enterocoely
* mesoderm forms pockets from gut
* Called deuterostomes
Differences between protostomes and deuterostomes
Innovation of coelom on animal phylogeny
Decribe Platyhelminthes (flatworms)
- A group under Lophotrochozoa
- Bilateral symmetric
- blastopore develops into mouth
- triploblastic
- no body cavity (acoelomates)
- ~25,000 species
- aquatic or terrestrial (moist) habitat
- “free-living” (scavengers) or parasitic (endo- or ecto- parasites)
- 1mm (flukes) to 10m (tapeworms)
- blind gut
Why is cephalization developed in animal
- Concentration of neurons and sensory structures at the anterior end
– sense organs probe environment
– enables directed locomotion - Sensory structures :
– mechanoreceptors (touch)
– chemoreceptors (taste/smell)
– photoreceptors (light)
Describe simple nervous system of animal
Four groups of Platyhelminthes
- Free living
1. Turbellaria (planarians) - Parasitic (+/-)
2. Monogenea (flukes, mostly ectoparasitic)
3. Trematoda (flukes, mostly endoparasitic)
4. Cestoda (tapeworms, endoparasitic)
Describe Tubellaria–“free-living, planarians”
- most are marine, some in freshwater, few in terrestrial moist
- Marine turbularians brightly colored, hunting protists/small animals. Blind digestive tube with tooth near middle of ventral surface
- Amazing ability to regenerate body
- Anterior end will always develop into a head b/c of molecular gradient. Studied for stem cells
- Reproduce asexually by fission & sexually (mostly hermaphroditic）
Describe Monogenea
- ectoparasites, flukes = flat body with suckers
Describe Trematoda
- flukes, endoparasites
- Schistosomiasis
-Caused by the parasitic trematodes called schistosomes.
-Common in Asia, Africa and S. America
-Disease rarely causes death but can damage internal organs and impair growth and development in children
Primary host– organism reaches maturity & sexual reproduction
Intermediate host – shorter transitional stage
Two larvae – sexual/asexual
Describe Cestoda
- tapeworms, endoparasites
- habitat: intestines of vertebrates (6,000 species described)
- adaptations:
scolex – suckers, hooks
proglottids – reproductive segments (unisex) - no mouth, no digestive system, specialized epidermis (for absorption)
- protective cuticle forms around embryos & terminal proglottids break off, passed via feces
- host-specific
Primary host: vertebrate
Intermediate host: insect, crustacean, mollusk
