BIO2231 - Arthropoda II - Subphylum Crustacea

Question 1

Subphylum Crustacea

Anatomy

5 points.

Answer 1

• Appendages primitively and typically biramous (with 2 branches) (insects, arachnids: typically uniramous)
• Two pairs of antennae (feelers)
• One pair of mandibles + two pairs of maxillae
• Body often divisible into cephalothorax and abdomen
• Respiration via external gills

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Question 2

What is considered a defining feature of crustaceans?

Answer 2

One pair of mandibles + two maxillae

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Question 3

What is noteable about Cephalophorax in crustaceans?

Answer 3

Cephalophorax is not homologous in crustaceans

Body typically divisible into abdomen and cephalothorax

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Question 4

Characters - Describe:

Homologous

7 points.

Answer 4

• Shared ancestry between a pair of structures (characters)
• Descent with modification from common ancestor
• Forelimbs in vertebrates: all derived from same ancestral tetrapod:
  • Wings of bats
  • Arms of primates
  • Front flippers of whales
  • Forelegs of dogs

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Question 5

Characters - Describe:

Analagous

2 points.

Answer 5

• Organs (characters) have similar function that were not present in the last common ancestor but rather evolved separately
• Wings of insects and birds evolved independently, and converged with respect to function to support powered flight

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Question 6

Characters

Are Homologus and analogous mutually exclusive?

Answer 6

Characters can be homologous at one level and analogous at another
Pterosaur, bird and bat wings are analogous as wings, but homologous as forelimbs

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Question 7

Describe Crustaceon

Respiration

3 points.

Answer 7

Respiration via external gills

Some exceptions

• Smaller species lack respiratory organs → Absorb O₂ through the body wall
• Most larger aquatic species have thoracic gills, featherlike structures.
• A few terrestrial species have “lungs”

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Question 8

Describe Crustaceon

Digestive system

2 points.

Answer 8

• One way tubular gut
• Complex stomach development in some groups

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Question 9

Describe Crustaceon

Excretory system

3 points.

Answer 9

• Via paired nephridia in the head
• Often called green glands, antennal glands or maxillary glands
• Nitrogen wastes excreted mainly in the form of ammonia

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Question 10

Describe Crustaceon

Circulatory system

2 points.

Answer 10

Open system - haemocoel and some distinct blood vessels

• Dorsal tubular or globular contractile “heart” with ostia opening to the pericardial sinus
• Blood pigments - haemoglobin and haemocyanin

Haemoglobin is sometimes conditional (Brine shrimp produce it only under oxygen stress)

Haemocyanin is disctinctive (purple)

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Question 11

Describe Crustaceon

Exoskeleton

3 points.

Answer 11

• Lacks the waxy waterproofing of arachnids and insects
• Bears a pigmented layer and a calcified layer
• One pigment commonly present changes from blue/green to red when the protein is denatured

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Question 12

Describe Crustaceon

Moulting

3 points.

Answer 12

• Cycle is initiated by environmental stimulus perceived by CNS
• Signal from CNS decreases production of Moult-Inhibiting Hormone from X-organ in brain
• Drop in MIH promotes release of Moulting Hormone from Y-organ near mandibles

Membrane ruptures (Between abdomen & carapace

→ old carapace separates and rises.

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Question 13

Describe Crustaceon

Life-cycle

4 points.

Answer 13

• Planktonic larval forms (Nauplius)
• Some have direct development
• Internal fertilisation
• Some reproduce via parthenogenesis

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Question 14

describe

Crustacea - diversity

7 points.

Answer 14

• Large > 67,000 species
• Most morphologically diverse of arthropods
• Dominant in marine environments (insects of the sea)
• Freshwater forms & few terrestrial
• Evolutionary interest
  • Maintains original marine arthropod design
  • Relation to Hexapoda

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Question 15

Crustacea

Class Ostracoda

4 points.

Answer 15

Seed shrimps

• Head and body enclosed in bivalve carapace
• Filter feeding (mostly, but also plant and carrion feeders and predators)
• Feeding and swimming with head appendages (at most 2 appendages)
• Important component of aquatic food webs (marine and freshwater)

May be paraphyletic based on recent DNA work

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Question 16

Crustacea

Class Malacostraca

6 points.

Answer 16

Crabs, shrimps, yabbies etc…

• Largest group of crustaceans
• Includes crabs, shrimps, yabbies etc
• But also slaters (terrestrial)
• Thorax typically 8 segmented
• Abdomen typically 6 segmented
• All segments bear appendages

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Question 17

Class Malacostraca

order Amphipoda

2 points.

Answer 17

• Laterally compressed, no carapace, second and third pair of trunk appendages often prehensile
• Marine, freshwater and terrestrial

High oxygen levels in the cold waters of Lake Baikal (Russia) allow for amphipods of larger than usual size

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Question 18

Class Malacostraca

order Isopoda

4 points.

Answer 18

• No carapace
• Marine, freshwater and terrestrial
• Dorso-ventrally compressed
• Uniramous antennae gas exchange A

Cymothoa exigua, or the tongue-eating louse, is a parasitic isopod of the family Cymothoidae. This parasite enters fish through the gills, and then attaches itself to the fish’s tongue. The female attaches to the tongue and the male attaches on the gill arches beneath and behind the female.

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Question 19

Class Malacostraca

order Euphausiacea

5 points.

Answer 19

Krill

• Marine
• Carapace does not cover gills
• No maxillipeds
• Very abundant
• Major food source for some fish and baleen whales

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Question 20

Class Malacostraca

order Decapoda

4 points.

Answer 20

Crabs, lobsters and crayfish/crawfish/crawdads

• First three pairs of thoracic legs modified as maxillipeds (for feeding)
• Leaving 5 pair of walking legs
• st pair often pincers (CHELAE, cheliped)
• Includes swimming forms and crawling forms

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Question 21

Subphylum Crustacea

Class Copepoda

6 points.

Answer 21

• Marine and freshwater
• Small (few mm or less)
• 1ˢᵗ segment of thorax fused to head
• No abdominal appendages
• 1ˢᵗ antennae typically long
• No gills

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Question 22

Class Cirripedia

Thecostraca

4 points.

Answer 22

Barnacles

• Filter feeding important component of inter-tidal zone
• Planktonic larvae
• Sessile
• 6 cirri: feather like appendages for feeding

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Question 23

Class Branchiopoda

order Anostraca

5 points.

Answer 23

Brine and fairy shrimp

• a.k.a. sea monkeys
• Restricted to inland waters especially saline lakes
• No maxillipeds
• Biramous 2ⁿᵈ antennae for locomotion
• Trunk appendages modified into leaf-like paddle for swimming and gas exchange

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Question 24

Class Branchiopoda

order Diplostraca

5 points.

Answer 24

Water fleas

• Common component of freshwater zooplankton
• Carapace laterally compressed, encloses the trunk but not the head
• Swim using 2nd antennae
• Filter feed using thoracic appendages
• May produce desiccation resistant eggs

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Question 25

Class Branchiopoda

order Notostraca

5 points.

Answer 25

Tadpole shrimp

• Freshwater
• Carapace dorso-ventrally flattened, covers head and thorax
• No rostrum, two pairs of reduced antennae
• Uniramous mandibles with no maxillipeds
• Many very old fossils known

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Question 26

Class Remipedia

3 points.

Answer 26

• Coastal saline cave dwellers
• Primitive condition?
• 2 Tagma
  • Head 5 expressed segments
    • Antennae x 2
    • Mandibles
    • Maxillae x 2
  • Trunk
    • similar segments
    • biramous app

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