L2 Bevan - Elasmobranch Diversity and Adaption 1 Flashcards
What are sharks fins used for?
1 or 2 dorsal fins - stabilizing
Pectoral fins - steering and lift
Pelvic fins - stabilizing
Tail/caudal fin - thrust
What is shark skin like?
Made up of dermal denticles/placoid scales, which are homologous in structure to teeth
Feels like sandpaper, they form a protective barrier and air swimming - reduce drag by delaying turbulence
How are shark teeth attached into the mouth?
They care not attached into the jaw, instead they sit in a membrane called a tooth bed
Tooth bed is like a conveyer belt, moving rows of teeth forwards as the shark grows and replacing teeth
How do you determine the age of a shark?
- counting growth rings on vertebrae or on spines in some species such as the dog fish
can live up to 70 years on some species
Give 5 reasons as to why we should study elasmobranchs
- protecting biodiversity
- top predator - are an indicator species
- there are many threatened species - from fisheries for fins, shark nets and incidental catch (by catch)
- little information is known about many species
- tourism
If sharks are no buoyant, how do the stay afloat the whole time?
Creating dynamic and or static lift
They can create dynamic lift like airplanes either with their outstretched pectorals ands lifting foils or inclining their bodies at AOA. Amount of dynamic lift is largely decided by the side and shape of pectoral fins
Downside = increased drag and energy
Why cant sharks create static lift?
Most (bony) fish create static lift with their swimbladder,
Sharks do not have that luxury:
low density building materials (cartilage instead of bone)
Oil is bulkier than air but fewer problems with buoyancy regulation. The lift provided by oil varies little with depth because changes in ambient pressure have little effect on the volume oil; so a shark that is neutrally buoyant at the surface will also be buoyant at the seabed even at great depth.
Sharks store oil in the liver and in the muscles, but they have to trade-off because the oil is also as a food store for the adult and/or embryo.
How many pairs of gills do sharks have and how do they work?
All sharks have 5-7 pairs of gills
GE occurs at the gills, and oxygenated water must always fow other the gills for GE to occur
Mouth –> phyarynx –> gills –> out via gill slits
What is the spiracle of a shark?
The spiracle is a basically a first gill slit.
Appears as an opening behind the eye. Used to provide oxygenated blood directly to the eye and brain through a separate blood vessel, and/or to pump water over the gills.
Absent in many sharks, e.g. fast swimming sharks
What is the spiracle used for in rays?
In rays, the spiracle is larger and more developed and is used to actively pump water over the gills to allow the ray to breathe while buried in the sand.
What are the ampullae of Lorenzini?
- are small vesicles (electroreceptors) that form part of an extensive subcutaneous sensory network system.
- They are found around the head and appear as dark spots
- each ampullae contain multiple nerve fibres that are enclosed in a gel-filled tubule
- they detect weak magnetic fields produced by other fish - allow sharks to locate fish buried in the sand
- may also be used for navigation
What is a sharks lateral line?
together with the AoL the LL comprises the electrosensory component of a sharks senses
It allows the shark to orient particle movement or sound
Consists of neuromasts which are located in canals just below the skin - can detect prey movements
What is sharks hearing like?
Sharks generally have sharp hearing, and hear through a small opening on the side of their head
What is the tapetum lucidium in a sharks eye for?
It is a reflective layer behind the retina, and consists of layers of plate like cells contain guanine crystals.
These reflect light that has already passed through the retina, restimualting the eye before it leaves - means visual is increased in low lights
Why does a hammer head
Hydrodynamic advantages (head is flattened on the lower surface and rounded on the upper and may therefore increase lift) Sensory enhancement. The nostrils of most species are located near the tips of the hammer and have specialised grooves which channel scent-bearing water to the nostrils. By having their nostrils mounted far apart they can sample the water column in stereo. The Lorenzini ampullae are distributed over the entire undersurface of the hammer, and the width of the head may work as a “metal prey detector”.
