Chelicerates

Question 1

Sea scorpions

Answer 1

Extinct now
2 tagmata - prosoma (head) and opisthosoma (abdomen)
Differentiation of appendages in this group = chelicera
Appendages after chelicera in other groups like pedipalps (not seen in sea scorpions)
4 more pairs of walking legs after this

Question 2

Horse shoe crabs morphology and features

Answer 2

Same group as sea scorpions
Marine
2 tagmata
Reduced chelicera and pedipalps
Gnathobase grind up food near mouth
Book gill - filled with blood in contact with sea water
Haemocyanin in blood, amoebocytes act as white blood cells (used for medical)
Compound eyes - very simple but important for detecting opposite sex

Question 3

Horse shoe crab reproduction

Answer 3

Form swarms when breeding

1. Females come into shallow water where males are
2. Females lay eggs and males go over and shed sperm on
3. Larvae develop in sediment

Question 4

Chelicerate general features

Answer 4

2 tagmata
Prosoma - 6 pairs of appendages = chelicerae, pedipalps and 4 walking legs
Opisthosoma - abdomen, not noticeable appendages
No distinctive head or antennae

Question 5

Arachnid characteristics

Answer 5

Terrestrial chelicarates
Mostly carnivorous
Use neurotoxins to subdue their prey through modified chelicerae, pedipalps or additional structure

Question 6

Scorpion morphology

Answer 6

Barb on end of tail - staining apparatus
Prosoma or cephalothorax and opisthosoma
Chelicerae aer tiny
Pedipalps enlarged and used for subduing prey (uses tail if doesn’t work)
Slits in abdomen leading to book lungs…
-looks like pages of book stacked, which are filled with haemolymph
-air can get drawn in through spiracle (beginning of stack) when gaseous exchange will occur

Question 7

Scorpion reproduction

Answer 7

Pedipalps used to grab mate
Fertilisation internal (terrestrial)
M drops spermatophore and places on ground
Leads F over to it
F takes it up in F reproductive opening and eggs become fertilised
F show parental care - give birth too
Offspring go on F back and looks after till they moult

Question 8

Spider morphology

Answer 8

2 tagmata - tiny waist between two allows particular movement of opisthosoma
Chelicerae modified as fangs (toxin)
Most are carnivorous
Pedipalps important in mating for males
4 pairs of walking legs
Usually have 8 eyes (varies as if catching prey with web, don’t need to see so well)

Question 9

Spider silk production and uses

Answer 9

Evolved in other arthropods too
Made of fibroin 
Produced in silk glands
Released fro spinnerets
Used for purposes like...
-for webs to catch prey
-for ballooning, releases it in threads, caught by winds allowing them to travel
-wrap food in silk - present for mate
-offspring wrapped in silk cocoon

Question 10

Internal systems of spiders

Answer 10

Have a book lung or tracheal system (evolved independently of insects) 
-lots of branching and delivers air to insects
Malpigian tubules (evolved independently of insects) similar to metanephridium
-substances drawn into haemolymph of tubules
-useful substances taken up, waste passed through

Question 11

Lifestyle of spiders

Answer 11

Predacious - use webs or jump onto prey (actively pursuing them)
Veggie spider - feeds on plant material on Beltian bodies (acacia bushes), have to be very quick to avoid ants

Question 12

Web builders…

Answer 12

Create stabilimentum…

• very elaborate
• thought to stabilise as counters weight of spider resting (rejected now though)
• not completely clear of purpose - stops birds flying into it?
• may attract prey or mates
• different functions in different spp

Question 13

Spider reproduction

Answer 13

F often bigger than M
F can eat M - not always
M modified pedipalps (longer than Fs) - to suck up sperm after they have deposited it, then inserting pedipalp into reproductive opening in F
Can use silk to keep F in place - ritual
Sometimes do courtship dances
Web-builders may pluck tunes spp specific
Huge sexual dimorphism in some groups - F gigantism and M dwarfism (selective pressures) - F = more eggs laid, M nimble & fast

Question 14

Co-operative spiders

Answer 14

Work together to catch prey in colony
Use silk where prey gets entangled and all attack
Can capture prey much bigger as consequence
Size dimorphisms as take on different roles

Question 15

Mites

Answer 15

8 legs or reduced
Free-living but parasitic too
Ear mites in cats - ignoble prize won’t by showing humans could get infected too (doctor infected himself)
Dust mites - live on dead skin, mattresses, pillows etc. can cause strong allergens due to enzymes present in faeces
Varroa - feeds on haemolymph of larva and pupa of honeybees
-causes weakness
-transmits deformed wing virus and others
-causes problems in colonies

Question 16

Ticks

Answer 16

4 pairs of walking legs
Ectoparasites feeding on blood
Ticks can transmit Lyme disease, caused by a spirochete (bacterium)
-can effect the NS and lead to paralysis

Question 17

Pycnogonids

Answer 17

Most of body is prosoma
Opisthosoma very reduced
Has 4 pairs of legs and proboscis
Chelicerae and pedipalps (confirmed is chelicerate)
No respiratory devices
Reproductive structures held on outside of body - males carries eggs once fertilised
Hooks called overtures on legs used for cleaning the legs and body