Cambrian And Ordivician Keywords

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Acoelomate

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- Animal that does not have a body cavity that separates the gut from the muscles of the body wall
- They instead have a mass of cells derived largely from mesoderm between gut and body wall
- Ex. Of acoelomates are flatworms

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Algal mats

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- Prior to Cambrian bottom sediments are covered in very dense algal mats
- Sitting on huge amount of organic material that is potential food
- Prevents other organisms from getting to this nutrient reserve

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Assymetric body plan

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- Body plan with irregular shapes that can’t be split into mirror-image halves
- Body plan found in most sponges

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Bilateral symmetry body plan

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- Animals that have left and right sides that are mirror images on either side of the bodies midline
- All metazoan fall in this group, the Bilateria, except Cnidaria and Ctenophora
- The Bilateria have anterior and posterior ends and dorsal and ventral surfaces
- Anterior end encounters environmental stimuli as it moves through it
- Cephalization favoured

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Bivalve

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- Clams, sessile environments
- Pump large amounts of water into their cavity using filter feeding strategy
- Burrowers

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Bryozoa

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- Lophophorates
- Forms reefs
- Sessile suspension feeders
- Each colony is produced asexually by a single animal

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Burgess Shale fossils

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- Most important fossils found from the Cambrian period, found in the Rocky mountains and in China
- Yoho National Park
- Found by a Dr. Walcott
- Fossils showed that the most diversity occurred during the Cambrian thus “the Cambrian explosion”
- Many unusual invertebrates

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Cambrian

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- Period of time where animal life is at its most diverse
- Increased calcium and mineral salts after erosion of snowball/ slush ball earth

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Cambrian burrowers

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- Ex. Priapulid worms (complete digestive tract)
- Pierced through algal matt and made available nutrient reserve underneath
- Without nutrients as a limiting factor new body plans would be experimented with

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Cambrian explosion

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- The beginnings of multi cellular life on earth
- Not multi cellular plants algae are the only primary producers
- All current animal phylum ancestors can be found in this period and they came about quickly
- Greatest animal diversity in earths history

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Carnivores

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- Animals that must eat other animals

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Cephalization

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- The development of an anterior head where the majority of sensory organs and nerve tissue are found
- Found in most bilaterally symmetrical animals

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Cephalopod

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- Squid molluscs
- Originally had conical shells, majority in the Cambrian
- Major predators in the oceans during Cambrian
- Remaining shelled member: nautilus

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Choanocyte

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- Collar of microvilli surrounding the single flagellum that moves in from the outside inward
- Traps smaller organisms in the water and consumes them phagocytosis
- A group of single-celled protists found in water, hollow ball-shaped body
- Possibly the common ancestor of all animals and all fungi

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Choanoflagellate

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- A group of single-celled protists found in water, vase shaped body
- Closely packed microvilli surround the single flagellum that allows movement and taking on food

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Cnidaria

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- Cnidocil is tweaked and nematocyst has a barb that shoots out and penetrates prey (works like a taser)
- Polyps are the original form
- Traps stings and pulls in and eats prey
- Jelly fish are an example
- Have first set of true tissues
- Endoderm: cavity is lined with nutritive cells that absorb nutrients, gland cells that produce enzymes and secrete them to break down food
- Ectoderm: nerve cells and cnidocyte
- No mesoderm

- Muscles on inside are arranged in a circle and outside are arranged in a linear fashion
- Endo and ectoderm are contractile

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Coelomate

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- have a fluid filled body cavity completely lined by mesoderm
- In vertebrates this lining is peritoneum a thin tissue derived by mesoderm
- The inner and outer layers of peritoneum connect forming mesenteries membranes that surrounds the internal organs and suspend them within the coelom

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Colonial choanoflagellate

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- Large aggregates: masses of cells with no cell-cell communication
- Could be a stalk or a matt
- Move water better together so they can potentially trap more food

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Corals

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- Sessile colony of single celled organisms
- Ancestors to coral reefs
- Hard scaly rocklike structure with a polyp coming out of it
- Part of group called Cnidaria

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Diploblastic

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- Body plan of embryonic layers that includes only two embryonic layers
- Only endoderm and ectoderm

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Doushantuo fossils

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- Fossils all spherical in shape
- Happen either just before slush ball/snowball earth or during
- Appear to be small fossilized early embryos
- Evidence of multicellular life prior to Cambrian or slush ball earth
- Could be large prokaryotes that are in large colonial forms

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Ectoderm

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- Outermost germ layer in metazoans that forms the external covering and nervous system
- Involved in animals with diploblastic and triploblastic body plans

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Ediacaran fossils

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- Just before Cambrian explosion is timeframe
- Found in Canada in Newfoundland
- Some of the oldest multi cellular fossils ever found
- Leaf like structures, too large to be single cells
- Tell us that there were some forms of multicellular life was before Cambrian but was lost during snowball earth

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Ediacaran period

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- Time period of the oldest multi cellular fossils found in the world

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Endoderm

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- Germ layer in metazoans that forms as the innermost tissue layer
- Develops into the lining of the digestive system
- In some animals also develops into the respiratory system
- Found in animals with diploblastic body plan and triploblastic bodyplan

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Filter feeder

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- Organisms that uses tentacles or other branch like structures to filter water for food and pull it into their mouths
- Ex. Annelids

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Gastropod

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- Mollusc marine snails
- Can prevent water loss and drying out by hiding in shell (why they are able to become terrestrial)

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Hermaphrodite

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Hermaphrodite
- Organism with both sets of sex hormones
- Useful trait as it allows both partners to produce offspring

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Homeotic genes

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- Ex. is the hox genes
- Structure genes for cell organization
- Patterning genes
- Make their appearance just before the Cambrian

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Homeotic mutants

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- Misplaced hox genes leading to structures being made in the wrong locations on an organism

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Hox genes

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- Homeotic genes
- Explanation as why the Cambrian has such a large diversity of animals
- Gives a pattern or structure for cell organization
- Found first in fruit flies
- Based on concentration of transcription factors in different locations in the embryo

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Hydrostatic skeleton

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- Key part of echinoderm movement
- How the starfish move their tube feet

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Lophophore

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- circular or “U” shaped fold (structure) with one or two rows of hollow ciliated tentacles surrounding the mouth
- involved in capture of food and serves as a site of gas exchange

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Medusa

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- Jelly fish, similar to a polyp except it is motile
- Medusa swims with ring of circular muscles around the bell that contract and bring the bell in which squirts water out
- Elastic skeleton

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Mesoderm

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- The middle germ layer in metazoans
- Forms the muscles of the body wall and most other structures between the gut

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Molluscs

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- Now squids, octopods, clams, snails
- Shells made by mantle
- Muscles run from shell down to foot so when contracted it can pull itself into the shell
- Muscular foot that allows it to move with all organs above it
- Second largest group of animals on the planet
- Feed with radula: distinct teeth on the tongue used to grind material off the substrate, makes fine particulate food

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Omnivores

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- An animal that feeds at several trophic levels, consuming plants, animals and other organic matter

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Onycophora

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- Velvet worms
- Highly predatory organisms
- Short stumpy legs
- Still alive on land with close to the same body plan

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Platyhelminthes

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- the flat worms
- acoelomate (no body cavity, solid organisms)
- Incomplete digestive tract, no anus
- Swim in a direction, oriented movement
- Bilaterally symmetric, anterior and posterior end
- Has cilia and hydrostatic skeleton for movement
- Hermaphrodite
- Specialist at feeding inside other organisms later on (parasitic)

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Polychaete

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- Marine worms, very diverse feeding situations
- Annelids
- Diverse body plans (worms so long cylindrical body plans)

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Polyp

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- Main feeding structure on the rocky coral sessile
- Hydrostatic skeleton
- Tentacles surrounding cavity with a mouth in the middle
- Tentacles trap food and put it in the mouth
- Feed on small invertebrates
- Carnivore
- Sit on tentacles at the bottom
- Cnidaria

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Pseudocoelomate

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- Animals that have a fluid-filled space between the gut and the muscles of the body wall
- No mesodermal lining around the endoderm
- Muscles derived from mesoderm from the outer lining of the pseudocoelom and its inner lining is the gut that doesn’t have muscles
- Internal organs are found within the pseudocoelom

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Radial cleavage

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- Typical of the deuterostomes
- The new top cells can balance right on top of the cells underneath

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Radial symmetry body plan

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- Animals with body parts that are arranged around a central axis like the spokes on a wheel
- The phyla that are considered radiata are the Cnidaria and Ctenophora
- any cut down the long axis divides these animals into matching halves

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Radula

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- tongue with teeth found in mollusks
- used to grind food off the substrate, makes fine particulate matter

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Seminal receptacle

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- receiving reservoir for sperm in hermaphroditic organisms
- found in flat worms

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Seminal vesicle

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- After sperm is produced in the testis it is sent for storage in this reservoir

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Slushball earth

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- States that earth is not covered entirely by ice and that at the equator there is still an area that is partly slush
- In this area primary production is still possible and continues
- Overall still a slowing point for lifes evolution as much of the earth’s primary produces aren’t working

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Snowball earth

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- As landmasses are above water for the first time 100 MA before Cambrian, erosion takes place which pulls CO2 out of the atmosphere
- Reduced atmospheric CO2 leads to a cooling on earth
- Poles freeze and grow larger and larger leads to so much of the planet covered in ice that earth reflects more energy from sun than it absorbs
- Results in earth’s temperature dropping so far it becomes a single frozen mass
- Much of life has trouble surviving because little photosynthesis is possible so oxygen levels are low
- Slowing point for evolution of life

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Spiral cleavage

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- Generally a characteristic of most protostomes
- From the four to eight cell division the cells on top orient themselves in the grooves or furrows between the cells below
- For this to happen the new cells on top must rotate themselves a bit to fit correctly

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Sponges

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- Relies on a special cell called a choanocyte
- Colonies of choanocytes make up sponges so they are not multi cellular because they are not made up of tissues that have specific roles
- Simplest and earliest body plans for multi cellular animals: two layered vase shaped structures, choanocytes lining the inside push water out the top and water moves in the replace it through pores
- Pore cell, choanocyte is a feed cell, pinacoderm made by pinacocytes amoebocytes will get food from choanocytes and transports it to other cells
- Division of labor between cells, but still at cell aggregate stage because not tissues
- Filter feeding, First group to work together in aggregates
- Meiosis: Choanocytes becomes sperm because it is motile, Archeocytes/Amoebocyte (sponge stem cells) form egg

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Spongocoel

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- The cavity of a sponge, with the opening called the osteopore found at one end

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Suspension feeders

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- Organisms that suspend structures above themselves to try to catch food that is falling to the ocean floor

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Transcription factors

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- Number of important protein factors that fold regions of DNA and put them under regulatory control
- Structure DNA to be able to make the right product

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Triploblastic

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- Most common embryonic layer body plan found in animals
- Involves all three germ layers
- Endoderm, Mesoderm, Ectoderm

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Tube feet

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- mini hydrostatic skeletons found on starfish arms, based on hydrostatic skeleton
- Used to capture food, grab food and pass it down with two feet to the mouth
- Have muscles that can move it back and forth
- Now used to crawl across the ocean

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Water vascular system

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- Found in sea stars make up tube feet system of sea stars