Molluscs: cephalopods

Question 1

What does ‘cephalopod’ translate as?

Answer 1

Head-foot.

Question 2

What animals does this group contain?

Answer 2

The octopuses, squid, nautiloids and ammonites.

Question 3

Cephalopods are the largest and most mobile, but the least intelligent, of the molluscs. True or false?

Answer 3

False: they are bad-ass in every way and probs more intelligent than most of the people at my secondary school.

Question 4

All species are marine predators. List some of their adaptations for this.

Answer 4

Complex eyes, a centralisation brain, rapid colour change.

Question 5

Describe the mating system of cephalopods.

Answer 5

They are dioecious with elaborate courtship routines.

Question 6

Where are the tentacles located?

Answer 6

The tentacles encircle the head.

Question 7

What are suckers used for?

Answer 7

Mobility and hunting.

Question 8

Describe an ammonite.

Answer 8

The mantle is external and very muscular. They move by jet propulsion: muscular contractions of the mantle coupled to siphon (modified foot) action.

Question 9

Are ammonites still alive?

Answer 9

No: they are from the paleo and Mesozoic eras.

Question 10

Describe a nautiloid.

Answer 10

A close relative of the ammonite that is still alive today.

Question 11

Both ammonites and nautiloids have coiled shells like gastropods. Do they also display body torsion?

Answer 11

No: the animal lives in a shell chamber instead of its whole body being twisted throughout the shell. The gladius is the internal chamber.

Question 12

What kind of lifestyle does an octopus have?

Answer 12

Benthic.

Question 13

What kind of lifestyle does a squid have?

Answer 13

Pelagic.

Question 14

Octopuses and squid have modified radulae. What other novel feeding structure do they have?

Answer 14

Beaks.

Question 15

Describe the cephalopod beak.

Answer 15

It is primarily composed of chitin and is very sharp. The upper and lower mandibles fit together and operate in a scissor-like fashion.

Question 16

What are the neocoleoidea?

Answer 16

They are the soft-bodied cephalopods, e.g. the octopi, squid and cuttlefish.

Question 17

The neocoleoidea possess ink sacs for predator evasion. How are these controlled?

Answer 17

The ink sacs are a muscular extension of the hindgut.

Question 18

How have neocoleoideans been modified in relation to their ancestral morphology? List 3 factors.

Answer 18

1. The shell become internalised or reduced
2. The mantle became enlarged
3. The foot was modified into a funnel and arms (the tentacles system)

Question 19

Describe the nervous system of neocoleoideans.

Answer 19

Extremely complex: there are approximately 500 million neurons in the CNS/PNS together.

Question 20

The ganglia are condensed in the brain. What protects the brain of neocoleoideans?

Answer 20

A cartilaginous capsule.

Question 21

How do neocoleoideans appear to learn? How do we know this?

Answer 21

By observation: the central vertical and optical lobes in the brain are highly developed.

Question 22

What kind of eyes do neocoleoideans have? Describe their eyes.

Answer 22

Camera eyes: they have extra ocular photoreceptors and a moveable lens for focusing. The lens is controlled by powerful muscles.

Question 23

It is thought neocoleoideans are sensitive to polarised light. Why?

Answer 23

Their photoreceptors are orthogonal (at right angles to each other). In octopi the pupil is a slit that is always kept horizontal as a result.

Question 24

Define a camera eye.

Answer 24

Whereby light enters the eye through a single opening and the eye is focused by moving the lens.

Question 25

Colour change of the entire skin is rapid and takes place in seconds. Give 3 functions of this.

Answer 25

1. Camouflage
2. Communication
3. Display

Question 26

Each neocoleoidean can produce approximately how many different appearances due to their colour changing ability?

Answer 26

~30-50, depending on species.

Question 27

Describe the skin of a neocoleoidean.

Answer 27

The skin is translucent: it has an underlay of leucophores and a covering of chromatophores and iridophores.

Question 28

Define a leucophore.

Answer 28

A white-reflecting cell.

Question 29

Define a chromatophore.

Answer 29

Pigments cells.

Question 30

Define an iridophore.

Answer 30

Iridescent cells.

Question 31

How are the chromatophores controlled?

Answer 31

They are tiny sacs of pigment. The organisms can control how much pigment is in the sac via muscle contractions.

Question 32

The skin can also change texture. How?

Answer 32

Via papillae controlled by muscle contraction and nervous.

Question 33

How does a neocoleoidean regulate its appearance?

Answer 33

By vision: the organism tries to match itself to its environment.

Question 34

Pelagic neocoleoideans do not have papillae. Why?

Answer 34

They do not need to change the texture of the skin: they are free swimming and have no need to blend into corals etc. like benthic species (octopi) do.

Question 35

Pelagic species, like squid, have more iridophores. Why?

Answer 35

For camouflage: they can control the iridophores on their underside to mimic those on their dorsal surface that are being hit by light from above. This makes them invisible to prey below.