Cephalopods - general features and pure crazy predators

Question 1

How have cephalopods evolved from generalised molluscs?

Answer 1

• Mantle cavity houses gills
• Nautilus has two pairs of gills, all others reduced to one pair
• Retain radula
• Mantle elongated/streamlined
• Reduced/absent shell
• Foot modified into funnel and tentacles and/or arms
• Closed circulatory system

Question 2

What are the 3 subclasses of cephalopods?

Answer 2

Ammonoidae, nautiloidea, coleoidae

Question 3

What are the general features of Nautilus?

Answer 3

• Has an external shell
• Found in tropical waters
• Animal lives in anterior-most chamber of shell
• New chambers grow behind, separated by septum
• Siphucle connects chambers
• Controls liquid levels in first chamber to maintain neutral buoyancy
• Diurnal migrations to feed
• Scavengers or opportunist predators
• 60-90 tentacles
• Simple pin hole eye
• Olfaction may be used for finding food
• Swim backwards by jet propulsion, contracting body into shell to expel water

Question 4

Describe what the chambers of the Nautilus shell are used for.

Answer 4

• Animal lives in anterior-most chamber
• New chambers grow behind, separated by septum
• Siphuncle connects chambers
• Controls liquid levels in first chamber to maintain neutral buoyancy

Question 5

What is the siphuncle of Nautilus?

Answer 5

The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod. Sucks fluid in or draws it out of the chambers to maintain buoyancy.

Question 6

Describe the general features of cuttlefish (Coleoidae, sub-order Decabrachia).

Answer 6

• Live in tropical/temperate oceans generally in shallows
• Internal shell, buoyancy controlled by gas/fluid filled spaces
• Swim by jet propulsion - muscular contraction
• Lateral fins offer stability and manoeuvrability
• Advanced eye
• 10 appendages - 8 short arms and 2 longer tentacles
• Rapidly extend tentacles to capture prey - suckers on end of tentacles/arms
• Predator species - crabs, fish and shrimp
• Use water jet to expose prey hiding in benthos
• Sit and wait predators
• Anti-predator ink sac

Question 7

Describe the general features of squid.

Answer 7

• Oceans around the world - pelagic
• 8 arms and 2 tentacles
• Some shallow living species and some deeper
• Huge variety in size
• Shell reduced to chitinous pen
• Retain buoyancy by replacing sodium with ammonium ions as these have a lower atomic mass
• Can jet at up to 40km/hr but usually only when escaping predators
• Active predators of fish, crustaceans and other squid
• ‘Tooth’ lined suckers and hooks aid in prey capture
• Advanced eye, similar to humans
• In deep sea species eye may function to spot shadows of sperm whales - sperm whales can eat up to 700 squid in a day

Question 8

Describe the general features of octopus (Coleoidae, sub-order Octopodiforms).

Answer 8

• Benthic living, found in all of the worlds oceans, range of depths
• 8 arms, no tentacles
• Loss of shell, only hard beak
• Neutral or negative, replace sodium with sulphate ions - heavier ions so they are denser and remain on sea floor
• Jet to escape predators, but mainly walk or swim
• Active hunters, prey on crustaceans, fish and often other molluscs
• Generally sit and wait predators
• Neurotoxins in salivary glands can paralyse prey - when they bite with beak, some species can inject neurotoxins
• Radula retained
• Chemosensors on suckers
• As with squid, have a well-developed eye

Question 9

What things make cephalopods great predators?

Answer 9

• Active swimming/jetting
• Closed circulation/gas exchange
• Vision
• Complex nervous system
• Colour change

Question 10

How do cephalopods carry out active swimming/jetting?

Answer 10

• Have a huge mass of muscle
• Radial muscles contract to reduce mantle thickness and expand mantle cavity
• Water sucked up into mantle and over gills
• Circular muscles contract, expelling water through siphon

Question 11

Why do cephalopods need a closed circulatory system?

Answer 11

Need to supply oxygen quickly to muscles

Question 12

Why is a large water flow required in the circulatory system of cephalopods?

Answer 12

Only one pair of small gills. Small gills offer less resistance to water flow but can absorb less oxygen. Therefore, a large water flow is required.

Question 13

What do cephalopods use for carrying oxygen instead of haemoglobin?

Answer 13

Haemocyanin

Question 14

How many hearts do cephalopods have?

Answer 14

3 hearts - 2 branchial hearts and a systemic heart

Question 15

Why is haemocyanin used instead of haemoglobin for oxygen transport in cephalopods?

Answer 15

More effective at carrying oxygen in cold waters than haemoglobin

Question 16

What do the 2 branchial hearts of cephalopods do?

Answer 16

Supply gills with deoxygenated blood

Question 17

What does the systemic heart of cephalopods do?

Answer 17

Pumps oxygenated blood to body

Question 18

What cephalopod is the only that does not have large, well developed eyes?

Answer 18

Nautilus

Question 19

Describe the eyes of cephalopods.

Answer 19

Spherical lens and square pupils. Convergent evolution with mammalian eye structure. Most are colour blind.

Question 20

What is convergent evolution?

Answer 20

Convergent evolution is the process by which independently evolved features that are superficially similar to each other can arise through different developmental pathways

Question 21

How does the complex nervous system of cephalopods aid in their ability as predators?

Answer 21

CNS shows cephalisation in the brain region. Larger than most fish, some reptiles and birds. Giant axons allow fast nerve impulses = escape responses.

Question 22

How have cephalopods shown intelligence?

Answer 22

Have the capacity to learn shapes and associations

Question 23

Why is the ability of cephalopods to change colour beneficial?

Answer 23

Increases effectiveness as a sit-and-wait predator in several environments. Can even change skin texture.
Camouflage - protection from other predators
Communication - use color patterns and displays to signal aggression, courtship, or territoriality. Establish social hierarchies.

Question 24

What are chromatophores?

Answer 24

Chromatophores are specialized pigment-containing cells located in the outer layer of the cephalopod’s skin called the chromatophore layer. They contain a single pigment which can create red, orange, brown, black and yellow colouration.

Question 25

What are iridophores?

Answer 25

Iridophores are cells containing reflective platelets that scatter and reflect light, producing iridescent colors such as blues, greens, and silvers. These cells are located in deeper layers of the cephalopod’s skin.

Question 26

What is colour change under control of?

Answer 26

Nervous system - activated by neural signals from brain