Molluscs: cephalopods Flashcards
What does ‘cephalopod’ translate as?
Head-foot.
What animals does this group contain?
The octopuses, squid, nautiloids and ammonites.
Cephalopods are the largest and most mobile, but the least intelligent, of the molluscs. True or false?
False: they are bad-ass in every way and probs more intelligent than most of the people at my secondary school.
All species are marine predators. List some of their adaptations for this.
Complex eyes, a centralisation brain, rapid colour change.
Describe the mating system of cephalopods.
They are dioecious with elaborate courtship routines.
Where are the tentacles located?
The tentacles encircle the head.
What are suckers used for?
Mobility and hunting.
Describe an ammonite.
The mantle is external and very muscular. They move by jet propulsion: muscular contractions of the mantle coupled to siphon (modified foot) action.
Are ammonites still alive?
No: they are from the paleo and Mesozoic eras.
Describe a nautiloid.
A close relative of the ammonite that is still alive today.
Both ammonites and nautiloids have coiled shells like gastropods. Do they also display body torsion?
No: the animal lives in a shell chamber instead of its whole body being twisted throughout the shell. The gladius is the internal chamber.
What kind of lifestyle does an octopus have?
Benthic.
What kind of lifestyle does a squid have?
Pelagic.
Octopuses and squid have modified radulae. What other novel feeding structure do they have?
Beaks.
Describe the cephalopod beak.
It is primarily composed of chitin and is very sharp. The upper and lower mandibles fit together and operate in a scissor-like fashion.
What are the neocoleoidea?
They are the soft-bodied cephalopods, e.g. the octopi, squid and cuttlefish.
The neocoleoidea possess ink sacs for predator evasion. How are these controlled?
The ink sacs are a muscular extension of the hindgut.
How have neocoleoideans been modified in relation to their ancestral morphology? List 3 factors.
- The shell become internalised or reduced
- The mantle became enlarged
- The foot was modified into a funnel and arms (the tentacles system)
Describe the nervous system of neocoleoideans.
Extremely complex: there are approximately 500 million neurons in the CNS/PNS together.
The ganglia are condensed in the brain. What protects the brain of neocoleoideans?
A cartilaginous capsule.
How do neocoleoideans appear to learn? How do we know this?
By observation: the central vertical and optical lobes in the brain are highly developed.
What kind of eyes do neocoleoideans have? Describe their eyes.
Camera eyes: they have extra ocular photoreceptors and a moveable lens for focusing. The lens is controlled by powerful muscles.
It is thought neocoleoideans are sensitive to polarised light. Why?
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.
Define a camera eye.
Whereby light enters the eye through a single opening and the eye is focused by moving the lens.
Colour change of the entire skin is rapid and takes place in seconds. Give 3 functions of this.
- Camouflage
- Communication
- Display
Each neocoleoidean can produce approximately how many different appearances due to their colour changing ability?
~30-50, depending on species.
Describe the skin of a neocoleoidean.
The skin is translucent: it has an underlay of leucophores and a covering of chromatophores and iridophores.
Define a leucophore.
A white-reflecting cell.
Define a chromatophore.
Pigments cells.
Define an iridophore.
Iridescent cells.
How are the chromatophores controlled?
They are tiny sacs of pigment. The organisms can control how much pigment is in the sac via muscle contractions.
The skin can also change texture. How?
Via papillae controlled by muscle contraction and nervous.
How does a neocoleoidean regulate its appearance?
By vision: the organism tries to match itself to its environment.
Pelagic neocoleoideans do not have papillae. Why?
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.
Pelagic species, like squid, have more iridophores. Why?
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.
