Lecture 12 - Arthropoda

Question 1

Explain Phylum: Arthropoda

Answer 1

• Jointed exoskeleton of chitin – moulting needed for animal to grow
• Segmented – some segments are fused
  - form head, thorax & abdomen
• Trilobites have one pair appendages per segment
• Limb specialization in modern arthropods

Nervous & sensory systems- well developed ( eyes, bristles, antennae can detect light, sound, vibrations, etc. )

• Respiration: gills (aquatic), book lungs (spiders) or tracheae (insects)
• Metamorphosis – complete or incomplete

Question 2

Explain metaphorphosis being complete or incomplete

Answer 2

• Complete as in butterfly: egg, caterpillar, pupa, adult
• Incomplete as in grasshopper: egg, nymph, adult

Question 3

What are the subphylum’s of Arthopoda

Answer 3

• Subphylum: Trilobita ( Trilobites are extinct )
• Subphylum: Chelicerata
• Subphylum: Myriapoda
• Subphylum:Hexapoda
• Subphylum: Crustacea

Question 4

Explain Subphylum: Crustacea

Answer 4

• Includes crabs, crayfish, barnacles, isopods
• Mostly marine with hard calcified exoskeleton
• Head: pair compound eyes, 5 pairs of appendages one pair each antennae & antennules, three pairs mouth parts- mandibles and two maxillae
• Serial hermaphroditism-gonad can swith from producing sperm to egg
• Most are carnivores
  - some are detritivores and filter feeders
• Biramous appendages on thorax & abdomen, in the form of gills and legs.

Question 5

Explain the Biramous appendages for Subphylum: Crustacea

Answer 5

• Forks from the basal protopodite
  - forms two branches, the inner endopodite and outer exopodite
• Each of these branches can be composed of either one or more segments

Question 6

What are examples of Subphylum: Crustacea

Answer 6

• Euphausids (krill), copepods
  
  • feed on algae
    - This forms part of zooplankton for fish, sharks, whales
• Isopods, amphipods
• Barnacles (sessile or stalked)
  - legs transformed to feeding appendages (filter feeding)
• Barnacle larvae are motile
• Octomeris angulosa, Tetraclita serrata, Lepas sp.

Question 7

Explain crabs; shrimp and crayfish fully

Answer 7

• Part of Subphylum: Crustacea
• Are decopods
• Possess 5 pairs of walking legs – 1st pair is clawed
• Head + thorax is fused to form the cephalothorax
• Gills are above walking legs: these are called biramous appendages
• Sexes separate - ♂ and ♀ appendages are found on the abdomen
• Blood vascular system open – haemolymph present
• Coelom reduced

Question 8

Explain Subphylum: Hexapoda


Answer 8

• Body is divided into Head , thorax and abdomen
• The head has mouthparts and sensory organs
• Three pairs of walking legs
• One or two pair wings
• Exoskeleton lighter than other arthropods

Question 9

Explain insects fully

Answer 9

• Grasshopper: jumping legs, 2 pairs wings, digestive system highly developed
• Respiratory system consist of tracheae + spiracle. No respiratory pigment present
• Excretory system is made up of– Malpighian tubules
• Blood system opens directly into a haemocoel
• Visceral organs located in the haemocoel are bathed in blood haemolymph
• Sexes separate ( Sexual reproduction )
• Metamorphosis – incomplete (grasshopper) or complete (butterflies)

Examples: Locusta migratoria, Princeps demodocus demodocus

Question 10

Explain Order: Lepidoptera

Answer 10

• Includes butterflies and moths
• Family Lycaenidae – most spp. of this family is endemic to Africa
• Lifecycle of this butterfly is linked to specific plant, ant species and confined areas
  Lycaenid butterfly larvae, are in a symbiotic relationship with ants, supply the ants with nectar

Question 11

Explain the lifecycle of a butterfly

Answer 11

• Eggs
• Caterpillar
• Chrysalis
• Butterfly

Question 12

Explain Subphylum: Myriapoda


Answer 12

• Include Centipedes and millipedes
• Centipedes –possess a head & trunk
• Body has many segments– 1pair walking legs per segment.
• Are predators with antennae and fangs
  Millipedes has a cylindrical body
• Some segments are fused
• It appears to have two pairs of walking legs per segment

Question 13

Explain Subphylum: Chelicerata

Answer 13

• Includes Scorpions and spiders
• First pair appendages are pincer-like and is called chelicerae – it has a feeding function
• Second pair is called pedipalps: it is used for feeding & sensory
• Possess 4 pairs of Walking legs
• A Cephalothorax is present (head and thorax are fused)
• And an abdomen (with internal organs)

Question 14

What are Advantages of a body cavity

Answer 14

1. Unrestricted body movement is possible
2. Complex digestive system can develop because of coelom
3. Hydrostatic skeleton to assist with movement
4. Coelom acts as a reservoir: eggs, sperm, metabolic waste(a place for storage)before being released
5. Thermo-regulation ability- glands and organs assists with this
6. Coelom protects internal organs from damage and temperature fluctuation
7. The coelom assists with Respiration and circulation of nutrients, carbon dioxide and oxygen