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Kina – Evechinus chloroticus Introduction


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Science Wananga – Kina Biology


Kina – Evechinus chloroticus
Introduction
Kina are sea urchins, a type of marine invertebrate that is related to starfish and sea cucumbers (all called Echinoderms). The scientific name of Kina is Evechinus chloroticus. The species is only found in New Zealand, from Northland through to Stewart Island.
Kina is the largest sea urchin and can reach 19 cm in diameter. They maybe very old!

They are also tasty, and are popular to harvest. This means we have to be sure we are not taking too many – we need to conserve them for the future.


Conserving a species requires knowledge on how many we can take in an area over a given time. To help manage this properly, we need to know something about its biology, especially how fast they grow, how old they are, what they eat and how they reproduce.
WHY ARE THESE FACTORS IMPORTANT?
Today we will look at some of this such as:

  • Remove a section of shell and try to age the individual. Pool the data and see if we can make a growth curve for your population

  • Look at how the animal reproduces



Kina – Evechinus chloroticus



Notes on fertilisation in marine invertebrates – Technical Stuff
Fertilisation involves the fusion of an egg and a sperm to form a zygote.
Sperm are short lived (hrs) and may be chemically attracted to eggs of the same species.
Once the sperm contacts the egg, it undergoes an acrosome reaction, a process that fuses the sperm to the plasma membrane, releasing enzymes from the tip of the sperm that digests the egg jelly coat.
A protein, bindin is also deposited on surface of the sperm, adhering it to the egg.
The binding of the egg is highly species-specific. So the sperm of one species cannot enter the egg of another species.




Polyspermy
Once bound, there are several steps to stop more sperm penetrating the same egg (i.e. polyspermy) and result in successful fertilisation:


  1. Fast block to polyspermy: In marine invertebrates, including kina, a fast block to polyspermy occurs within a tenth of a second of fusion.

Sodium (Na+) flows into the egg cytoplasm, depolarizing the membrane. This stops extra sperm from fusing to it.


The plasma membrane is restored to normal within minutes.


  1. Slow block to polyspermy: The fertilization envelope is a physical barrier to stop further sperm penetration.

A calcium wave flows from the site of sperm attachment, releasing cortical granules which enzymatically detach the vitelline layer from the egg plasma membrane (see diagram above).



Question: If polyspermy occurs, how many copies of the genome does an egg contain?

Question: What happens to the pattern of cell division if polyspermy occurs?

1. Fertilization process
Oocytes from the urchin Evechinus chloroticus have been spawned at the beginning of the laboratory.
1. Examine oocytes on a slide with a compound microscope using the 40x objective.
2. While you are observing the eggs, have your partner add 1 drop of sperm to the egg mass.
Question: Did you observe the moment of fertilization?

Describe any change in the colour/morphology of the egg membranes?

3. Fertilize a larger quantity of eggs (30 ml) in a 250 ml beaker; add approximately 200 ml of filtered seawater and leave to stand on the lab bench. Remove a sample of eggs after 10 minutes and observe the fertilization membrane. Remove and observe a sample of eggs after one hour and just before you leave the laboratory.
Question: How far did development proceed?

10 mins:


1 hr:


2. Early embryo development
After fertilisation, the single cell eggs undergo a series of cell divisions that result in a hollow sphere of cells called a blastula.

Radial Cleavage (Deuterostomes)




Radial Cleavage – Kina
Kina undergo radial cleavage.
Kina cleavage results in more cells, but without an increase in the total volume of the embryo.
Once the larvae start feeding, their size will increase.
Examine, draw and label the fertilised egg:

  • fertilization envelope

  • hyaline layer

  • cell membrane


Fertilised Egg

Kina Dissection
External Anatomy

Draw the external anatomy of the kina (don’t attempt to draw all the spines, only a small area) and label the following: Test, primary spines, secondary spines, tube feet, peristomal membrane, mouth, jaws, gonopore, madreporite, anus, oral surface, aboral surface.


Dissection Technique

  1. Measure diameter of your kina with a ruler.




  1. Turn the animal upside down and, using a sharp pair of scissors, make a hole through the peristomal membrane.




  1. Using the scissors, make a clean straight cut around the equator of the animal until the animal splits in two.




  1. You should now be able to see the internal structures of the animal.




  1. Remove the Aristotles Lantern and examine the jaws, ligaments and mussels.


Internal Anatomy

Observe, draw and label the following structures: Test plates, aristotles lantern, intestine, oesophagus, water vascular system, mouth, anus.




Aging
1. Measure the diameter of the animal

2. Take a piece of the shell.

3. Bleach it

4. Sand it down.

4. Place some vegetable oil on the shell and view under a microscope.

5. How many rings can you count? If one ring = 1 year, how old is you animal?





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