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35 Cards in this Set
- Front
- Back
What are cephalopods? What two cephalopods are we studying? |
Cephalopods are mollusks, related to bivalves and gastropods - very mobile pelagic predators with good eyesight - quite intelligent compared to other mollusks -Octopi and squid are common ex. of cephalopods w/o shell two cephalopods with external shell 1. nautiloids 2. ammonoids both entirey marine |
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What are the 4 problems for evolution for the external shell, representing by a ball? |
Problems with external shells 1. Buoyancy - as ball is much denser than seawater, it would sink 2. Instability: stability is conferred on an object by separation of centres of boyancy and mass. - if centre of mass and buoyancy occur in same position,would be very unstable shape 3. Hydodynamic inefficiency: high drag 4. Hydrostatic pressure: increase as water depth increases |
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Give an overview of Nautilus 1. when started 2. where they still occur 3. depth max |
Nautilus evolved in the Ordovician, still extant, whereas ammonoids did not evolve until Devonian mass extinction that occurred at the end of the Cretaceous Nautiloids still extant today belong to genus Nautilus These animals occur in 15 degree area near equator in Pacific Ocean. e.g Fiji, New Caledonia, Philippines Found up to 600 m deep |
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Describe the Planispiral shell |
Planispiral shells coil in single horizontal plane, shell diameter increasing away form coiling axis. - each 360 degree revolution of shell is called a whorl, the very outside edge of each whorl is called the venter |
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Describe Nautolid morphology between living chamber and phragmocone |
Internally a Nautiloid shell consist of two main parts. 1. Living Chamber: houses the soft body of the animal
1a. soft body includes: 90 tentacles which help with food gathering and reproduction 1b. hyponome, folded one piece flap that resembles a tube for use in jet propulsion, 1c. a digestive system, gills, and a reproductive organs 1d. eyes lack lenses, vision is quite poor 1e. opening in shell where soft bod projects aperture 2. Phragmocone, made up of a series of gas-filled chambers or camerae - camerae are seperated by hard cross-pieces called septa 2a. soft tissue Siphuncle runs through centre of chambers connecting them to mantle cavity - siphuncle consists of blood vessle, nerves and cells in organic sheath, key role in controlling buoyancy |
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How do Nautilis feed? |
Nautilus are reef predators and scavengers Tentacles are sticky and can extend to grab prey as it passes. --> pass food to mouth, located in middle of circle of tentacles mouth has beak-like jaw, tears up the food and cracks open the shell of prey if necessary food is processed by hard radula, before being swallowed into digestive track |
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How to Nautilis move? |
Nautilus swim using jet propulsion Water is drawn into the mantel cavity, then sealed-off. --> creates rise in hydrostatic pressure Hyponome is opened and water is forcibly ejected from the mantle by retraction of the body into the conch, as well as hyponome and mantle muscles Can move hyponome so water jet can be directed at any angle, controlling direction of movment Can attin speed of up to 0.5 m, using jet propulsion |
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What are the two fucntions of a cephalopods shell? |
Functions of shell 1. protection of bulnerable body 2. control the animal's buoyancy Cephalopods are very slightly negatively buoyant |
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How do shells deal with buoyancy problem? |
Cephalopod's shell is 3 times denser than sea water Problem solved by lowering overall density. Achieved by filling the chambers of phragmocone with gas 1/800th density of sea water |
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Describe buoyancy control as the shell grows |
As animal grows, it adds new chambers to phragmocone. when new chamber is first formed, it is filled with liquid As the animal grows and becomes heavier, it gradually removes liquid from newest formed chamber. Cephalopod able to empty chambers using siphuncle, which connects mantle cavity to the chambers Liquid in the chambers is hypo-osmotic when compared to blood, which fills the siphuncle Creates a significant salinity difference between siphuncle and the chambers, creating osmotic gradient across wall of siphuncle Gradient cause liquid to move from chamber into siphuncle, where it is removed. Process creates vacuum, vacuum causes air to enter chambers from the siphuncular tissues via passive diffusion gas pressure in chamber always remain less than 1 atms because of passive diffusion |
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Shell: Osmotic pressure vs. Hydrostatic Pressure What is the composition of Shell air? |
Gas than enters the chambers from the siphuncle is air, higher CO2 and lower O2, suggest it is respirated air |
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Why do Nautilus keep a small amount of water in their shells |
Ward revealed that Nautilus never completely empty their chambers of its phragmocone. Small amt of liquid remains in each chamber Allows Nautilus to make small changes to its depth by emptying or refiling its chambers with liquid - animal does this by altering salt concentration on the chamber side siphuncle ex. if want to go deeper, salt ions are actively removed from the chamber. If not, chambers would flood with liquid as hydrostatic pressure would be increased comapred to osmotic |
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Limitations of the the shell System |
Nautilus cannot swim too deep ~ hydrostatic pressure increase with 1 atms every 10 m pressure inside chambers of phragmocone always remains at less than 1 atms Shell and septa must be strong enough to bear increasing external pressure. Nautilis scan only swim up a maximum of 600m |
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Movie - Planet Earth Ocean deep 1.Why do Nautilus ascend to the water surface? 1.Why do Nautilus often bump into things when they are moving through the water column? 2.What animals are the closest living relatives of Nautilus? 3.Which animal is one of the Nautilus' major predators? 4.How do Nautilus detect predators and prey? 5.Other than jet propulsion, what is another function for the animals hyponome? 6.How often do Nautilus need to eat? |
n/a |
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Describe the growth of the nautiloids |
- only certain amount of liquid available to be pumped out of each chamber before it is empty animal must produce more chambers as it increases in size, to maintain near neutral buoyancy animal adds to anterior portion of shell so that when it is time to produce a new chamber, animal can move forward in its shell chamber liquid is then secreted behind the body, before the animal produced a new septum to close off new chamber chamber remains full of liquid until the new septum is about 1/2 its final thickness at this point, septum is strong enough to withstand hydrostatic pressure exerted on it form body chamber, animal can begin to remove liquid animal grows new chamber every two weeks until reaching maturity |
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Describe the earliest nautiloids from the ordovician |
Nautiloids from Ordovican to recent earliest nautilods were straight-shelled cones that faced down towards the substrate. - main scavenging nd predatory animals in early Paleozoic earliest nautiloids are classified as either longicones or brevicones |
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Compare Longicone and Brevicone shells |
Longicones have shells that expand slowly during growth. Pointed apical end approximately 10-15 degrees. Makes shell long and thin. Brevicones shells expand quickly during growth. Apical end angle of 20-25 degrees Makes shell short and fat |
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Describe the features and stability of straight-shelled cephalopods |
Further apart centre of mass and buoyancy are, less likely animal will be spun around by external forces in straight-shelled cephalopod, COB is 3/4 way down axis of cone when measured from the apical end - this point is dependent on shape of the shell and cannot be changed by variations in the distribution of various components within the shell COM is towards the body chamber, where heavy tissues are. COM is affected by changes in orientation of heavy tissues inside shell. Thus it moves as animal grows, or changes the position o its body while swimming. |
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What is the advantage Brevicones have over longicones |
Brevicones had advantage in that they were more stable. Brevicones - had wider seperation between COM and COB. Centerof mass near aperature Longicones- had narrow seperatio between COM and COM, further away form aperture |
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Now what are the disadvantages of brevicones |
Brevicones were at great risk from predators 1. Most brevicones face straight down, with an aperture that was wide open, imagine tentacles hanging directly down 2. shells had very high drag. very inefficient shape to move through the water column and were very poorly adapted to speed Brevicones limited to Early and Middle Ordovician |
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How were he brevicones weaknesses solved by the longicones? |
Longicone: counterweight principle 1. Added weight to apical end of shell, functioned as counterweight to soft body of animal, tipping the soft body away from the substrate 2. lowered the animals drag Longicones are divided into 3 groups based on how they employed the counterweight 1. Orthocerids 2.Actinoceratoids 3. Endoceratoids |
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Describe how Orthocerids approach the counter weight principe cyrtocones |
Orthocerids: range from Ordovician to Triassic They had cameral deposits of calcium carbonate at the apical end of their shell As alternative, some groups of orthocerids did cyrtoconic coiling groups called cyrtocones, have a light bend to their shell Does same thing cameral deposits. ITs coiling helps reduce drag for deviatiing from straight shell |
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Describe how actinoceratoids approach the counter weight principe cyrtocones |
Actinoceratoids: Ordovician to the Mississippian Had siphuncle deposits of calcium carbonate which infiled the siphuncle at the apical end Siphuncle still remain connected to individual chambers of phragmocone via a narrow pore, which remained empty of Caco3 |
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Describe how endoceratids approach the counter weight principle cyrtocones |
Endoceratoids: evolved from nautiloids range from Orodovician to Siluarian Large siphuncle that could reach sizes of 5 cm in diameter offset form centre of the shell Offset siphuncle displaced mass of animal to one side Furthermore, in endoceratoids, apical end of enlarged sipuncle was infille dwith cones made of Calcium carbonate |
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Describe the coiled nautiloids |
Coiled nautiloids with planispiral shells occur in the Silurian and are still extant Two main benefits 1. Reduces drag 2. adds strength to the shell, spherical shell produces ore even distribution of hydrostatic forces shell of coiled nautilods are very thick, 3 mm to add strength |
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Ammonoid v Natuilods: Difference in posion of siphuncle |
Ammonoids evolved from nautiloids in Devonian Nautiloids, siphuncle runs through middle of septal faces in center of chambers of phragmocone. Ammonoids: siphuncle is ventral, outer edge of phragmocone chambes |
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Ammonoid v Natuilods: Differences in septa orientaion |
Nautiloids: septa are concave. Making last septum relatively weak Ammonoid septa are convex, better to resist implosion form hydrostatic pressure |
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Difference in shell thickness between Ammonoid and nautiloids |
Nautiloids have thicker shell, 3 mm Ammonoid shells are thinner at 1 mm |
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Difference in shell shape between Ammonoid and nautiloids |
Nautiloid shells are more globular in shape Ammonoid shells vary much more in shape in a spectrum from compressed to depressed. Compressed forms are proportionately narrow. Depressed forms are relatively fat. Compressed forms have significant advantage over more gobular or depressed forms in hydrodynamic efficiency whorl height, whorl width, wtf? page 31 |
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Difference in sutural complexiity between Ammonoid and nautiloids |
Suture line is often preserved at the junction where each septum meets the animal shell. Suture lines look like lines on the outside of the internal mould flat areas of shells are weakest areas for resisting implosion from hydrostatic presure Nautiloids with their globular shape, have no weak flat areas. Thus the outside edges of their septa are very simple and correspondingly, geometry of suture lines are very simple. Nautiloid shells are further strenghtened as they are quite thick In contrast, in ammonoids, shell shape vary from compressed to depressed, shells sometimes have flat areas, much weaker for resisting hydrostatic pressure Ammonoids deal with this problem by changing the shape of their septa. Middle of septa are simple, but outside edges are complex outside edges of septa are more complex, suture lines are more complex |
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Describe the septa as butresses and compare difference in compressed and depressed ammonoids |
sutures as buttresses increase strength allows variation in shell shape, and thinner shell in compressed ammonoids, where flat areas occur on the vertical plane, the buttresses are horizontal In depressed ammonoids where flat areas occur on horizontal plate, buttresses are vertical |
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Describe the morphology of ammonid septal suture lines |
Ammonoid septal suture lines include two regions. Saddles and Lobes Parts closer to animal body is called saddles, while part further from animal is lobes. Sit on saddle and lie on lobes |
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Describe septal suture lines and the first goniatite ammonoid group |
Three different styles of ammonoid septal suture lines that divide the group of ammonoids Goniatite: have simple saddles and simple lobes. Mostly had a globular shape, although some were somewhat compressed. Had thinner shells, which helped improve efficiency in buoyancy. Firs occured in Middle Devonian and ended in Permian |
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Describe the Ceratite ammonoids |
Ceratite: Ceratites have ceratitic septal suture lines. Septal sutures have simple saddles and filled lobes Mostly globular in shape although some were somewhat compressed Thinner shells, improved efficieny for buoync Permian to the Triasic |
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Describe the Ammonite Ammonoids |
Ammonite: ammonitic septal suture lines. Frilled saddles and frilled lobes. These are the most comples suture lines. Vary in shape from compressed to depressed, had thinner shells Late Permian to end Cretaceous mass extinction |