Cephalopods Flashcards
In what way are cephalopods record breakers?
- they are the smartest, largest and fastest
What are the general body features of molluscs?
- radulla: teeth used to scrape or drill holes
- mantle: covers body and produces shell
- foot to move
What are the general body features of cephalopods?
- modified foot: arms and funnel
- mouth with a beak
What are the key features of the nautilus shell?
- chambers added as they grow
- chambers allow for buoyancy to be altered and to maintain upright position
- counter-shading for camoflage
- siphuncle perforations through the septa
What are the different types of tentacles that the nautilus has?
- digital tentacles: anchor
- lateral tentacles: grope around
- median tentacles to move food to mouth
How is sensitivity increased in the tentacles of the nautilus?
- increased surface area with lamella (ridges) and ciliary fields
- the cilia for mechanosensory are shorter
- the cilia for chemosensory are longer
How do the nautilus eyes work?
- pinhole camera
- light travels through the hole and arrives at a point on the back of the eye which is composed of light sensitive cells
What issues must the nautilus overcome with pinhole eyes?
- if eyes small: focused but dim
- if eyes large: bright but fuzzy
- must produce mucus from goblet cells to clear pathogens from the eye (since seawater and sediment gets in)
What study was conducted to examine the visual acuity of nautilus eyes?
- Muntz et al
- nautilus put in tank surrounded by drum with stripes
- if the nautilus could perceive the stripes it would turn with the drum to orient itself
- minimum visual resolution between 5 and 11 degrees (two objects must be more that 5 degrees apart to be perceived)
How do the cephalopods differ in supporting structures?
- nautilus: shells
- squid: flexible rod
- octopus: beak
- cuttlefish: bone
How do the squids use jet propulsion?
- shoot water out funnel
- can aim funnel to direct themselves
What type of circulatory system do squid have?
- closed circulatory system
- supports their active lifestyle
What does not having a shell risk and what is gained?
- higher risk of being eaten
- better manuverability
What tentacles do squid use for predation?
- two long tentacles
- end called tentacle clubs and contain suckers
- tentacle stalk
What kind of eyesight do octopuses have?
- lens to focus light
- lens is moved back and forth to focus light
- light enters eye and hits the photoreceptors at the back
- octopuses are able to see polarized light because of microvilli
What is the octopuses organ of equilibrium? What is it used for?
- complex statocytes that are made up of base, macula, and three cristae
- cristae detect angular acceleration
- macula detects forward acceleration
- to gain information about body position and movement
What adaptation/abilities do cuttlefish have?
- lateral lines that contain hair cells that detect movement in water
- useful for avoiding predators
What is used for colour changing in cephalopods?
- chromatophores: sacs filled with pigments (black, brown, red, orange, yellow)
- chromatophores are under nervous system control and are connected to radial muscle fibers
- reflecting cells: located below chromatophores and three different types (blue and green, iridophores: pink, yellow, green, blue and silver, leucophores: white spots)
- stellate ganglion relays from brain to change colour pattern
What else do octopuses do aside from change their colour for camoflage?
- mimic octopuses change their behaviour to appear like flounders, lion fish, and sea snakes
What defense mechanisms do cephalopods have?
- ink jet to produce curtain
- photophores are bioluminescent and may be involved in mating or defense
How do cephalopods know which chromatophores to use for counter shading?
- they use temperature
- warmer in shallow water: green
- colder in deeper water: blue
What is unique about the vampire squid?
- see colour
- live in the deep so only see bioluminescents
How do the pacific giant octopus mate?
- female detects fitness level of potential mates with chemosensory
- if chosen she cracks their sperm packet over her eggs
- she airates the eggs until they hatch and then she dies
What is the relationship between body weight and brain weight in some cephalopods?
- larger brains compared to body weight then fish and reptiles but less than birds and mammals
