Arthropoda - Crustscea

Question 1

What general features do arthropods share?

Answer 1

Jointed limbs and other appendages
Insects have evolved flight
Bilaterally symmetrical 
Bodies covered by exoskeleton 
May have evolved from annelid worm or several different times over history

Question 2

What implications arise from the integument?

Answer 2

Need for periodic moulting
Restriction of permeable surfaces for respiration - limits size of most species
Greater resistance to water loss
Grouping of segments of common function which are often fused
Exoskeleton becomes heavier as size increases
Ingrowths enable muscle attachment

Question 3

Describe the structure of the integument

Answer 3

Composed primarily of chitin
Has four layers;
- epicuticle (outermost) waxy, water impermeable and cannot serve for gas exchange
- procuticle (2 layers) - exocuticle (hard outer layer secreted before a moult) and endocuticle (soft inner layer secreted after a moult)
- epidermis (innermost) single layer of epithelial cells that secretes the cuticle

Question 4

Describe the process of ecdysis

Answer 4

Shedding of old cuticle is periodic but moulting process and preparation for it are continuous
Under hormonal control
During premoult, old cuticle becomes thinner
New cuticle forms inside degenerating old one
Newly emerged animals stretch new cuticle to full size by taking in air or water
Outer layer is hardened by sclerotisation

Question 5

Name the branchings of Arthropoda

Answer 5

Arthropoda
Mandibulata Chelicerata Trilobites
Pancrustacea myriapoda
Insects many others

Question 6

What are the main points and characteristics of the Crustacea?

Answer 6

Major subphylum of the Arthropoda, terrestrial freshwater and marine
Biramous limbs and a hard exoskeleton
~67,000 species 84% of which are marine
Dominate plankton and are important in benthos
13% freshwater 3% terrestrial

Question 7

What are the main points and functions of the biramous limb found in Crustacea?

Answer 7

Can be used for swimming, walking, feeding, respiration, sensory or for eating
Chela (plural chelae) are the pincers and are biramous limbs

Question 8

Describe the crustacean development

Answer 8

Egg develops into larva
Larva is known as the nauplius
Nauplius has three pairs of jointed limbs, used for locomotion and feeding
1st pair become antennae, 2nd and 3rd become 2nd antennae and mandibles
After several moults, 4th pair of appendages appear. This stage is the metanaupilus stage

Question 9

Name the 7 classes of Crustacea

Answer 9

Remipedia
Cephalocarida
Malacostraca 
Thecostraca
Oligostraca 
Branchiopoda
Copepoda

Question 10

Main points with regards to arthropods?

Answer 10

1 million+ species, 80% of all named animal species
Highly successful, represented in nearly all habitats
Pollinators
Create/maintain soil
Agricultural pests
Disease vectors
Seafood
Critical in most food chains
Primary converters of plant to animal tissue

Question 11

Define the class Remipedia and give an example of a species within this class

Answer 11

Small group, generally deep cave dwellers
Found globally
~20 species known
Primitive body plan, head, elongate trunk, 42 similar body segments
Swimming appendages are lateral on each segment and the animals swim on their backs.
Lack eyes
Fangs connected to secretory glands, are venomous
Lasionectes exleyi

Question 12

Define the class Cephalocarida

Answer 12

Horseshoe shrimps
~12 species
Small, benthic marine animals less than 4mm long
Feed on organic detritus in mud or sand sediments
Range from intertidal zone to waters 1500 metres deep

Question 13

Define the class Malacostraca

Answer 13

Includes crabs, shrimps, prawns, lobsters, aphipods, Decapods, krill and woodlice
>25,000 species in 16 orders
Perhaps the most diverse range of body forms in the animal kingdom
Marine, freshwater and terrestrial
Three tagmata (body regions) - head (5segments) thorax (8segments) and tail (usually 6segments)
Head has 2 pairs of antennae
Usually pair of stalked compound eyes

Question 14

Name and describe the main orders of the Malacostraca

Answer 14

Decapoda - 10 footed, crabs crayfish, lobsters, prawns and shrimp - ~15,000 spp.
Isopoda - woodlice, hog louse etc - 5000 terrestrial, 4500 marine and 500 freshwater spp. ~10,000 spp
Amphipoda - freshwater shrimp and sandhoppers
Euphausiaca - krill

Question 15

Define the class Thecostraca and give an example of a species

Answer 15

Barnacles ~ 1320 spp.
Generally sedentary or parasitic as adults but planktonic as larvae
Feed on plankton and detrtitus using modified legs from within their shells
Parasitic species Sacculina carcini parasitises a species of crab causing it to become infertile and care for the barnacle as if it were its own egg sac

Question 16

What are the three subclasses of the Oligostraca?

Answer 16

Ostracoda - ~13,000 spp. Small diverse group
Icthyostraca - tongue worms - obligate parasites
Branchiura - fish lice ~150spp

Question 17

Define the class Branchipoda

Answer 17

Includes brine shrimp, fairy shrimp and water fleas
Diverse but unified but the presence of gills on many of the animals appendages, including mouthparts
Mostly freshwater, some marine
850+ spp. Mostly water fleas

Question 18

Define the class Copepoda

Answer 18

Copepods - ~13,000 species
Around half of which are parasitic
Abundant in oceans
Around 400 freshwater spp.