Chelicerata

Question 1

What animals does Chelicerata contain?

Answer 1

It is a subdivision of Arthropoda
Horseshoe crabs
Sea spiders
Arachnids

Question 2

Chelicerata anatomy

Answer 2

• Two main tagmata: prosoma and opisthosoma
• Prosoma: formed by tagmosis of 6 embryonic segments, many have a carapace
• Opisthosoma: formed by tagmosis of up to 12 embryonic segments plus post-anal telson (last segment of abdomen), may be undivided (spiders) or segmented (scorpions)

Question 3

Appendages of the Chelicerata prosoma

Answer 3

• No antennae or true mandibles
• 1 pair of chelicerae (jointed feeding or mouth-parts known as pincers or fangs)
• 1 pair of pedipalps (usually sensory, can be pincers)
• 4 pairs of walking legs

Question 4

Appendages of the opisthosoma (reduced but still present)

Answer 4

• Book-gills (for locomotion and respiration) in horse-shoe crabs
• Spinnerets (for silk manipulation) in spiders

Question 5

What is the scientific name for sea spiders?

Answer 5

Pycnogonids

Question 6

Features of pychnogonids (sea spiders)

Answer 6

• Marine arthropods
• 1300 species
• 4 pairs of very long legs
• Commensals or ectoparasites of invertebrates
• Small body
• Digestive system that extends into their legs

Question 7

What is the scientific name for horseshoe crab?

Answer 7

Xiphosura

Question 8

Features of xiphosura (horseshoe crab)

Answer 8

• 4 living species
• Large carapace protects the prosoma
• The opisthosoma is fused
• At the base of each walking leg is a structure called a gnathobase (jaws)
• 480 Ma fossils found that are ancestors

Question 9

What is the scientific name for sea scorpions?

Answer 9

Eurypterids

Question 10

Features of Eurypterids (sea scorpions)

Answer 10

• Extinct, found in the Ordovician to Permian periods (460-248 Ma)
• Prosoma had a head shield
• Unfused opisthosoma

Question 11

Scorpions

Answer 11

• Widespread arachnids
• Venomous telson
• 1730 species
• All tropical and warm environments
• 4 pairs of walking legs
• 2 chelicerae
• 2 pedipalp

Question 12

Spiders

Answer 12

• 45,700 species
• Very disparate ecologies
• Spin silk
• Take down prey with venom
• Loss of visible external segmentation of opisthosoma
• 4 pairs of walking legs
• Pedipalp for sensation and sperm transfer
• Orientation of chelicerae: plesiomorphic (forward-facing) or apomorphine (derived, lateral formation)
• Basal part of chelicerae has poison gland
• Book lung with trachea for respiration
• Haemocoel containing harmocyanin carries oxygen
• Spinnerets - opisthosomal appendages for spinning silk
• 8 eyes in 4 pairs
• Main eyes and secondary eyes

Question 13

Features of spinnerets

Answer 13

• Silk comes out of spigots
• Spools used to manipulate the silk
• Multiple silk types produced by different glands for different purposes

Question 14

Features of a web

Answer 14

Huh (middle)
Frame (edge)
Catching spiral

Question 15

Purpose of secondary eyes in spiders

Answer 15

Have a reflective tapetum lucidum, which makes them good in low light level vision and for movement detection

Question 16

What are the main eyes in jumping spiders?

Answer 16

Image forming camera eyes

Question 17

Palipgradi

Answer 17

Microwhip scorpions
80 species
Blind, interstitial soil dwellers
Tropical and subtropical

Question 18

Pseudoscorpions

Answer 18

3300 species
Small arachnids
Common in leaf litter
superficially resemble real scorpions

Question 19

Solifugae

Answer 19

Sun spider / camel spider
1000 species
Live in arid environments, under stones, in burrows or grasslands

Question 20

Opiliones

Answer 20

Harvestmen / daddy longlegs
6500 species
Do not produce silk or toxins
Capable of ingesting particulate food, unlike real spiders

Question 21

Acari

Answer 21

Muted and ticks
50,000 species
Most are free-living, some are parasites
Common in aquatic and terrestrial environments