Crustaceans

Question 1

Crustaceans are the most diverse group of animals on Earth. True or false?

Answer 1

True.

Question 2

How many extant species are there?

Answer 2

~68,000.

Question 3

Within the arthropods which group are the crustaceans a sistergroup to, under both the pancrustacea and mandibulata hypothesis?

Answer 3

The hexapods.

Question 4

Define Orsten fauna.

Answer 4

Fossilised crustaceans preserved in Orsten lagerstätten from Sweden.

Question 5

Why are Orsten fauna good for looking at crustacean growth and evolution?

Answer 5

They are preserved in nodules at different growth phases

Question 6

What are yicaris dianensis and wujicaris muelleri?

Answer 6

Some of the earliest fossilised crustaceans from the Cambrian

Question 7

Where were yicaris dianensis and wujicaris muelleri found?

Answer 7

China.

Question 8

Why is the term Eucrustacea sometimes used?

Answer 8

It refers to all extinct and extant forms of the crustacean but excludes the trilobites

Question 9

Give 3 features of eucrustacea.

Answer 9

1. The body is split into 3 distinct segments: head, thorax and abdomen
2. The head and thorax are often joined in the cephalothorax which is often covered by a carapace.
3. Each body segment has paired appendages.

Question 10

What is another name for the abdomen of crustaceans?

Answer 10

The pleon.

Question 11

How many pairs of appendage does the head have?

Answer 11

3: the antennula and antenna (sensory) and the mandibles (crushing mouth parts)

Question 12

How many segments/pairs of appendages does the thorax have?

Answer 12

There are 5 segments each with a pair of limbs, hence the term ‘decapod’.

Question 13

The abdomen often pairs pleopods. What are these?

Answer 13

Swimming legs.

Question 14

Define the terms a) pereiopods and b) maxillipeds - these are found on the thoracic segments.

Answer 14

a) Walking legs

b) Feeding legs

Question 15

Define carcinisation.

Answer 15

When a crab-like form evolves from a non-crab-like ancestor. The crab-like form has evolved convergently multiple times.

Question 16

There are 6 major groups of crustacean. What are they?

Answer 16

1. Malacostraca
2. Branchiopods
3. Ostracods
4. Maxillopods
5. Remipedia
6. Cephalocarida

Question 17

Which group is the most diverse?

Answer 17

Malacostraca.

Question 18

What are stomatopods?

Answer 18

Mantis shrimps, members of the malacostraca.

Question 19

What is characteristic about the abdomens of shrimps?

Answer 19

They often have limbs on, unique in crustacea.

Question 20

There are 2 types of mantis shrimp, each with different limb forms. What are they?

Answer 20

a) spearing limbs

b) smashing limbs

Question 21

Describe how the smashing limbs of mantis shrimps work.

Answer 21

With an acceleration of 10,000g the limb creates a cavitation bubble (vacuum) in the water. The combined blow from the limb and from the bubble generate a force of up to 47,000 times their body weight. Helps to smash open prey like molluscs.

Question 22

What is a snapping mantis shrimp?

Answer 22

Shrimps with modified smashing arms: from a distance of 3-4mm a shrimp can shoot a cavitation bubble at a target, causing a snapping sound.

Question 23

The bubbles from snapping mantis shrimps are louder than whale and dolphin song. True or false?

Answer 23

True!

Question 24

Stomatopods have highly evolved eyes.

a) How many photoreceptors have they got in each eye?
b) How many fields of vision can they see in?
c) They need both eyes for depth perception. True or false?

Answer 24

a) 12: 8 for colour, 4 for UV
b) 3: colour, UV and polarised light
c) False: they can see depth with only one eye

Question 25

There are 6 major groups of crustacean. What are they?

Answer 25

1. Malacostraca
2. Branchiopods
3. Ostracods
4. Maxillopoda
5. Remipedia
6. Cephalocarida

Question 26

What are the only crustaceans to display eusociality?

Answer 26

Stomatopods.

Question 27

Where do stomatopod colonies live?

Answer 27

Inside sponges.

Question 28

Branchiopods are tadpole shrimps. They have evolved androdioecy. What is that?

Answer 28

Whereby individuals are only ever larger hermaphrodites or smaller males. This is to prevent a loss of genetic diversity by ensuring sexual reproduction.

Question 29

The maxillopodans are highly segmented and often parasitic. Give 2 examples.

Answer 29

1. Branchiura or ‘fish lice’

Question 30

The maxillopodans are highly segmented and often parasitic. Give 2 examples.

Answer 30

1. Branchiura or ‘fish lice’

2. Pentastomids have no segments or brain but live in the tracheal system of amphibians and reptiles.

Question 31

The maxillopodans are highly segmented and often parasitic. Give 2 examples.

Answer 31

1. Branchiura or ‘fish lice’

2. Pentastomids have no segments or brain but live in the tracheal system of amphibians and reptiles.

Question 32

Give an example of a maxillopodan that is not parasitic.

Answer 32

The thecostracans or ‘barnacles’.

Question 33

Describe the body structure of a thecostracan.

Answer 33

Descended from shrimp-like ancestors, their heads are secured to a rock surface and the thorax has been lost. Some also argue the abdomen has been lost because abdominal gene-B is missing.

Question 34

Give a similarity between the remipedes and cephalocarids.

Answer 34

They are both homonomously segmented, meaning all their segments are identical as opposed to the other crustaceans.

Question 35

What is unique about the remipedes?

Answer 35

They are the only crustaceans to produce venom.

Question 36

Describe the toxicity of remipede venom?

Answer 36

It has 12 known toxins in it, one of which causes anaphylactic shock, another causing spastic paralysis of the muscles.

Question 37

Why is it thought that remipedes have developed venom?

Answer 37

As an adaptation to the dark, they live in submarine caves.

Question 38

Differentiate between a venom and a poison.

Answer 38

Venom = a chemical that causes harm when injected or by infecting a wound

Poison = a chemical that causes harm when ingested