Just as dives can be shallow, middling or deep, our knowledge of the wonderful marine life we meet in UK waters can be basic, good or extensive.
Which is not to imply for one moment that shallow dives are in any way basic, I hasten to add - in fact they are among my favourites, because you get to see so much more, in better light and for longer.
Anyway, use this quiz to establish the depth of your marine-life knowledge. Note that Latin names arent expected even in the deep questions (with one worthwhile exception),but are included in some answers for completeness and clarity.

a = Shallow, b = Middling, c = Deep
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1a) What are these spectacular animals
1b) Why has the one on the right got such bold stripes
1c) What are their eggs often known as
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2a) What is a very familiar name for this animal
2b) Where does it usually live
2c) What are its three other common names
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3a) What are these colourful creatures
3b) What do they feed on
3c) Roughly how many have been recorded per square metre in their dense aggregations
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4a) What type of animal does this close-up show
4b) Which species is it
4c) What is the function of the groups of bumps around the spines
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5a) Which species is this, often found on wrecks
5b) What other colours does it come in
5c) Why does it look as if something has been nibbling its base
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6a) What type of animal is this
6b) Is it male or female
6c) Which species is it
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7a) Is this seaweed
7b) What group does it belong to
7c) What is said to be its characteristic smell
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8a) What type of animal makes the yellow bumpy structure
8b) How does it feed
8c) What makes this species unusual
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9a) What would happen if you trod on this fish in the shallows
9b) What is it
9c) What is the best way to reduce the effect
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10a) What is this animal
10b) What does it eat
10c) How can tiny amounts of pollution from anti-fouling paint affect it
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11a) To what group does this colourful fish belong
11b) Why is it so colourful
11c) Whats it doing here
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12a) Is this animal more closely related to a sea cucumber, fan worm or coral
12b) What is it
12c) Whats special about this species
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13a) Why is this starfish such a peculiar shape
13b) Which species is it
13c) What is the obvious white spot on its body
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14a) What is this fish
14b) Which close relative is virtually extinct around most of the UK
14c) Why doesnt it clog up its gills when it lies in the sand
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15a) Is this pair of velvet swimming crabs mating
15b) When is a female crab ready to mate
15c) Is this crab a herbivore, carnivore or omnivore
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16a) What type of animal is this
16b) What is its delightful name
16c) What are its less-than-delightful land-based relatives
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17a) Is this a blenny or a goby
17b) Which species, and where is it found
17c) What colour does the male turn when guarding eggs
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18a) What sort of animals are these
18b) Which species
18c) What is so special about their larvae
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19a) Is this a jellyfish to steer clear of
19b) What type is it
19c) What are the little fish often found living among its tentacles
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20a) What animal is this
20b) What is its Latin name
20c) Where does it breed
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