Lesson 16 - Cephalopds (Nautiloids And Ammonoids)

Front 1

What are cephalopods?

What two cephalopods are we studying?

Back 1

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

Front 2

What are the 4 problems for evolution for the external shell, representing by a ball?

Back 2

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

Front 3

Give an overview of Nautilus

1. when started

2. where they still occur

3. depth max

Back 3

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

Front 4

Describe the Planispiral shell

Back 4

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

Front 5

Describe Nautolid morphology between living chamber and phragmocone

Back 5

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

Front 6

How do Nautilis feed?

Back 6

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

Front 7

How to Nautilis move?

Back 7

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

Front 8

What are the two fucntions of a cephalopods shell?

Back 8

Functions of shell

1. protection of bulnerable body

2. control the animal's buoyancy

Cephalopods are very slightly negatively buoyant

Front 9

How do shells deal with buoyancy problem?

Back 9

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

Front 10

Describe buoyancy control as the shell grows

Back 10

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

Front 11

Shell: Osmotic pressure vs. Hydrostatic Pressure

What is the composition of Shell air?

Back 11

• water will not empty out of a chamber if the osmotic pressure between the chamber liquid and blood of the siphuncle is greater than the hydrostatic pressure difference between the chamber and sea water

• Ambient air pressure is 1 atms, at sea water surface and increases by 1 atms for every 10m of water depth

• soft boy of animal is liquid filled
• means that pressure in body chamber is same as ambient pressure, varies depending on the depth of animal in water column
• 200 m - 21 atms pressure
• As animal swims deeper, osmotic difference across siphuncle must be increased to exceed hydro static pressure, or else chambers will flood

Gas than enters the chambers from the siphuncle is air, higher CO2 and lower O2, suggest it is respirated air

Front 12

Why do Nautilus keep a small amount of water in their shells

Back 12

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

Front 13

Limitations of the the shell System

Back 13

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

Front 14

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?

Back 14

n/a

Front 15

Describe the growth of the nautiloids

Back 15

• as nautiloids grow, they get heavier affecting buoyancy

- 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

Front 16

Describe the earliest nautiloids from the ordovician

Back 16

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

Front 17

Compare Longicone and Brevicone shells

Back 17

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

Front 18

Describe the features and stability of straight-shelled cephalopods

Back 18

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.

Front 19

What is the advantage Brevicones have over longicones

Back 19

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

Front 20

Now what are the disadvantages of brevicones

Back 20

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

Front 21

How were he brevicones weaknesses solved by the longicones?

Back 21

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

Front 22

Describe how Orthocerids approach the counter weight principe cyrtocones

Back 22

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

Front 23

Describe how actinoceratoids approach the counter weight principe cyrtocones

Back 23

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

Front 24

Describe how endoceratids approach the counter weight principle cyrtocones

Back 24

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

Front 25

Describe the coiled nautiloids

Back 25

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

Front 26

Ammonoid v Natuilods: Difference in posion of siphuncle

Back 26

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

Front 27

Ammonoid v Natuilods: Differences in septa orientaion

Back 27

Nautiloids: septa are concave. Making last septum relatively weak

Ammonoid septa are convex, better to resist implosion form hydrostatic pressure

Front 28

Difference in shell thickness between Ammonoid and nautiloids

Back 28

Nautiloids have thicker shell, 3 mm

Ammonoid shells are thinner at 1 mm

Front 29

Difference in shell shape between Ammonoid and nautiloids

Back 29

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

Front 30

Difference in sutural complexiity between Ammonoid and nautiloids

Back 30

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

Front 31

Describe the septa as butresses and compare difference in compressed and depressed ammonoids

Back 31

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

Front 32

Describe the morphology of ammonid septal suture lines

Back 32

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

Front 33

Describe septal suture lines and the first

goniatite ammonoid group

Back 33

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

Front 34

Describe the Ceratite ammonoids

Back 34

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

Front 35

Describe the Ammonite Ammonoids

Back 35

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