Arthropoda

Question 1

Arthropods are

Answer 1

• bilaterally symmetrical
  
  • triploblastic
  • coelomate:
  • reduced coelom: the haemocoel forms the body cavity: open blood system (as in molluscs)
    -metamerically segmented (as in annelids)
    -double ventral nerve cord
    tough, chitinous exoskeleton, so
    -moulting occurs
    -jointed limbs

Question 2

Cilia

Answer 2

No cilia
so:
-no ciliary feeding
-sperm are amoeboid or packaged into spermatophores

Question 3

Subphylum Crustacea

Answer 3

biramous (2-branched) limbs
-two pairs of antennae
the basic crustacean larva is a nauplius

Question 4

Subphylum Chelicerata:

Answer 4

Two classes: Arachnida (spiders, scorpions, etc.)
Merostomata (horseshoe ‘crabs’:just one extant species)
- no antennae or mandibles
- limbs uniramous:
1 pair of chelicerae (often with poison)
1 pair of pedipalps (sensory)
4 pairs of walking legs

Question 5

Class Merostomata:

Answer 5

Limulus polyphemus chelicerates with abdominal limbs
are all extinct

Question 6

Class Arachnida:

Answer 6

• no abdominal limbs
• larvae as juvenile adults

Question 7

Subphylum Uniramia (onychophorans, myriapods & insects)

Answer 7

1 pair of antennae
-limbs uniramous
(- 2 pairs of maxillae)
-primarily terrestrial or freshwater
(larvae neither marine nor planktotrophic)

Question 8

Uniramia diversity

Answer 8

three classes:
Myriapoda: millipedes and centipedes
Hexapoda (≈ Insecta): the insects
Onychophora: velvet worms (e.g. Peripatus, Peripatopsis)

Question 9

Class Myriapoda (millipedes and centipedes)

Answer 9

• elongate:
  many segments
• 1 pr of legs per seg(centipedes)
  or 2 pr (millipedes) of legs per segment
• terrestrial

Question 10

Class Hexapoda (insects, fishmoths, etc.)

Answer 10

Subclass Insecta (insects)
- three tagmata (head, thorax, abdomen) head with 3 pr mouthparts: mandibles maxillae labium (fused 2nd maxillae)
-thorax 3-segmented, each segment with a pair of legs
-thorax with 2 pairs of wings
-no abdominal limbs

Question 11

insect respiratory system

Answer 11

tracheae deliver oxygen directly to tissues

Question 12

Insect reproduction:

Answer 12

cleidoic egg:

• resistant to desiccation
• gas exchange across shell

Question 13

Advantages of larval stages:

Answer 13

-larval / nymphal stages exploit different food from adults (like marine larvae)
-in the sea, larvae are the dispersal phase

Question 14

Why are the insects so successful?

Answer 14

cuticle: resistance to desiccation, heat stress
Exoskeleton: protects against damage
Moulting: new, stronger, protective skeleton can be produced
physiology: malpigian tubules, rectal pads conserve water
mouthparts: variety of food possible
flight: dispersal, food from 3 dimensions
life cycles: short; rapid increase in no’s, can recover from disaster
adaptability: variety of habitats variety of lifestyles
small sizes: occupy microhabitats; fast lifecycles, rapid evolution
Sociality: live in colonies where individuals work together
i.e. hugely adaptable,  many species

Question 15

The onychophorans –

Answer 15

Are they arthropods??
- wormlike, segmented
- soft exoskeleton
- cilia present
- one pair of unjointed legs/segment
- malpigian tubules and tracheae
- terrestrial, predatory (slime glands)
- viviparous (bear live young)