Lecture 10 - Arthropods - 1

Question 1

how big is the group?

Answer 1

largest group of animals

Question 2

what is a big feature of the group?

Answer 2

they are metamerically segmented with appendages on segments

Question 3

what is tagmatisation?

Answer 3

groups of segments e.g. head, thorax, abdomen - each section is tagmata

Question 4

what are hox genes and when were they first discovered

Answer 4

first discovered in an arthropod - drosophila

• control anterior-posterior axis
• tell cells in body which segment they are in and what they are going to be by coding for regulatory proteins

Question 5

how have arthropods adapted to be resilient to desiccation and move onto land?

Answer 5

they have a cuticle secreted by the epidermis

Question 6

describe the 2 parts of the cuticle

Answer 6

epicuticle - at the top made up of proteins and wax - waterproofing layer
procuticle - made up of exo,endo and mesocuticle - the exocuticle is a tanned glycoprotein making it very strong

Question 7

describe arthropod locomotion

Answer 7

• not peristalsis due to hard covering
• muscles attached directly to cuticle
• appendages have a thinner cuticle

Question 8

arthropod circulation

Answer 8

haemocoel - have a heart but is open circulatory

Question 9

arthropod gas exchange

Answer 9

special structures because cuticle is impermeable allowing no diffusion

Question 10

how do arthropods grow?

Answer 10

process called ecdysis - shed old cuticle and grow a new one - molting is when new features will form in development from young - epicuticle is shed because tanning makes it too tough to be broken down - endocuticle is digested by enzymes secreted by epidermis

Question 11

what limits the size of arthropods

Answer 11

the cuticle - because if they grew large they would need a thick cuticle which would be too heavy

Question 12

why is the new cuticle very soft?

Answer 12

allows the animals to grow - they make the cuticle bigger than themselves by absorbing water or puffing themselves up with air which they get rid of when the cuticle hardens

Question 13

describe the oldest group of arthropods

Answer 13

trilobites

• 3 body regions (head thorax tail)
• compound eye
• binamous limbs

Question 14

describe the chelicerates

Answer 14

• 2 body regions (prosoma, opithosoma)
• 6 pairs of appendages
• chelicera = pincers and pedipalp = first walking leg

Question 15

marine chelicerates

Answer 15

horseshoe crab - only survivors out of sea scorpion group - very unusual
- blue blood with lots of amoeebocytes acting like RBCs

Question 16

terrestrial chelicerates

Answer 16

arachnids - scorpions, mites, ticks and spiders

Question 17

how do most arachnids feed

Answer 17

mostly carnivorous and use some kind of toxin to kill prey

Question 18

4 facts about scorpions

Answer 18

• earliest group of arachnids
• chelicera v reduced and pedipalps are massive
• reproduction - internal fertilisation - male drops a spermatophore
• stinging tail which injects neurotoxin

Question 19

6 facts about spiders

Answer 19

• chelicera are modified into fangs which deliver toxins
• pedipalps are important in mating
• spin silk produced by silk glands - made of protein fibroin
• usually have 8 eyes
• book lung for gaseous exchange - some also have tracheae system
• malphigian tubules as excretory device

Question 20

use of silk by spiders

Answer 20

• ballooning for travel
• gifts for females
• wrapping offspring
  can make the silk a different consistency depending on what they need it for

Question 21

describe mites

Answer 21

free living and parasitic forms

• dust mites eat dead human skin - live in mattresses- faeces contain allergens
• varroa - feed on haemolymph of honey bees - can cause collapse of a colony

Question 22

describe ticks

Answer 22

ectoparasites - fill up their abdomen with blood of vertebrates
- can transmit lyme disease - effects nervous system

Question 23

what are sea spiders called and whats different about them?

Answer 23

pycnogonids - most of body is prosoma - opisthosoma is tiny