1. Chelicerata 1. Pycnogonida - marine, ‘pycnogonids'
2. Merostomata - the horseshoe crabs
3. Arachnida - contains all the terrestrial chelicerates … 18 orders (7 ‘major’)
features: chelicerae, no evidence of antennae
widely separated from other ‘arthropods’

3. chelicerae should be contrasted with the antennae (arising on same embryonic segment) in other arthropod groups
in many chelicerate groups food is processed by the modified bases of some anterior appendages (= ‘gnathobases’)

4. Pycnogonida ‘sea spiders’ small and isolated group
may be ‘sister group’ to other arthropods
characterised by ‘head’ structures:
proboscis
chelifores + chelae
palp structure
ovigers
body extremely reduced, organs in leg base

6. Merostomata horseshoe crabs (Xiphosura, Limulus)
western side of Nth Atlantic and Nth Pacific Oceans
characterised by:
carapace
chelicerae
book gills
relationships with the other chelicerates are based more on tradition than other evidence

7. Arachnida Body organised as prosoma/opisthosoma
Prosoma appendages of arachnids:
1 pair of chelicerae
1 pair of pedipalps
4 pairs of legs
chelicerae, pedipalps & legs I often highly modified
Opisthosomal appendages vary
18 orders (7 ‘major’)

8. Scorpion - a generalised arachnid

12. Arachnida Eurypterida (extinct) Uropygi Palpigradi Solifugae
Scorpiones
Araneae
Schizomida
Amblypygi
Ricinulei
Opiliones
Pseudoscorpiones
Acari (7 Orders)

13. Arachnida - Eurypterida, Scorpiones, Pseudoscorpiones, Araneae

14. Eurypterida ‘sea scorpions’ marine/freshwater … 450+Ma - c 250 Ma
size range medium to gigantic Pterygotus rhenaniae (~ 380Ma) 1.8m long
now generally regarded as basal stock from which other arachnids radiated

15. Scorpiones most plesiomorphic of extant arachnids
prosoma is covered by a solid carapace dorsally; ventrally by the coxae of the legs.
opisthosoma segmented (primitive) and divided into preabdomen and postabdomen.
telson modified to form sting
chelae short, strong, feeding appendages
pedipalps large, chelate, grasp prey
presence of cuticular UV fluorescent layer

16. Scorpiones - ecology
sting has a sharp point, penetrates integument of prey or enemy venom produced in adjacent poison glands, injected by voluntary muscular action
mostly sit-and-wait predators, operate from burrows or refuges
VERY fast reflexes
vision very limited
use vibrations to create 3-D world picture
trichobothria and sensory setae/slit sensillae
grasp and tear vs touch and sting
reproduction - spermatophore … maternal care

18. success of scorpions
morphologically very conservative – have found a niche/niches and are exploiting it/them
moderately speciose (1000s of species)
can be VERY abundant
extreme generalists in prey taken
considerable diversity – many niches

20. Pseudoscorpiones
body and appendages are more highly modified than in scorpions.
pedipalps chelate, used for prey capture, have poison glands in the finger or hand and opening at the tip
chelicerae short, strong, used to open prey comb on the chelicera cleans buccal cavity
silk glands on chelicerae used to make retreats
reproduction - spermatophores, maternal care of young

22. success of pseudoscorpions
very important component of ‘cryptozoa’
moderately speciose (1000s of species)
can be VERY abundant (>106/ha found)
hooked into small insects/mites/soft-bodies as a resource
considerable diversity - many niches

23. Spiders - Order Araneae
about sp described
likely estimates indicate 2-3x this number
spiders are the most highly derived group within the chelicerates
ancestral chelicerates resembled scorpions
defining synapomorphies
chelicerae modified to fangs
structure of silk glands and spinnerets

24. Features: the great many uses of silk.
the utilization of venom and diversity of feeding habits.
the well developed vision of some hunting spiders.
evidence for a high degree of behavioural plasticity.

25. Four major groups of spiders are recognised:
Mesothelae (= Liphistiomorpha) - segmented abdomens, mid-ventral spinnerets, 4 book lungs, paraxial chelicerae. (& fossils c 300Mya)
Mygalomorphae - terminal spinnerets (segmented), 4 book lungs, paraxial chelicerae
Hypochilomorphae - diaxial chelicerae, 4 book lungs (relicts - 1 USA, 1 China, several Australia & NZ - gradungulids etc)
Araneomorphae - diaxial chelicerae, 2 or 0 book lungs

26. Relationships:
(Mesothelae(Mygalomorphae(Hypochilomorphae, Araneomorphae)))
Mesothelae, Mygalomorphae grades?

27. Mesothelae suborder of their own two genera: Liphistius, Heptathela
~ 40 species recognised
Japan, East Asia to Indonesian region
4 booklungs, paraxial chelicerae, mid-ventral spinnerets
abdomen has dorsal segmental sclerites!
occupy silk-lined burrows with trapdoors

28. Opisthothelae Mygalomorphae
‘primitive’ group
~ 2000 species
4 booklungs, paraxial chelicerae
terminal spinnerets, often segmented
ambush predators from silk-lined burrows (sometimes with trapdoors) or bivouac retreats

29. Opisthothelae Araneomorphae
‘true spiders’
2 divisions recognised
Hypochilomorphae, Araneae
terminal spinnerets, diaxial chelicerae

30. Araneomorphae Hypochilomorphae
relicts … ~ 40 sp, 8 genera
Hypochilidae (USA, China - 2 sp), Austrochilidae (Tasmania, S. Am.), Gradungulidae (southern NZ, Australia)
4 booklungs, semi-diaxial chelicerae
web-builders and ‘snatchers’

31. Araneomorphae Araneae
‘ordinary spiders’
most diverse and ecologically successful spiders - 30,000+ species
2 or 0 booklungs, tracheae
web-spinners (diverse kinds), cursorial hunters

32. Anatomy
two body divisions:
prosoma
opisthosoma

34. Prosoma chelicerae  fangs (synapomorphy of spiders)
pedipalps - manipulation, mating (in  )
4 pairs of walking legs
eyes - most 8, many 6, rare <6 (sometimes 0)

35. Opisthosoma
booklungs
reproductive openings
spinnerets

36. Chelicerae (= fangs) derived from chelate feeding organs sub-chelate
paraxial vs diaxial organisation

37. Pedipalps
sensory
manipulation
mating
embolus

39. Walking legs
spiders one of the arachnid groups lacking extensor muscles - run on hydraulics ... short, high-speed bursts.
walking
leaping

40. Sensory structures eyes trichobothria slit sensillae
single
lyriform organs
chemosensory organs

41. Eyes primitively 8, some 6, rarely 0 around anterior margin/on turret
general form
special forms
salticid (jumping spider) eyes

42. Trichobothria
long, thin setae attached to socket … extensively innervated at socket
only on appendages (legs mainly)
may be constrained to linear movement
VERY sensitive to air movements
may also be used to monitor vibrations in the web or along silk lines

43. Slit sensillae single lyriform organs how they function
appearance, structure
amplify flexing of exoskeleton
lyriform organs
fields of slit sensillae … very sensitive
how they function

44. Chemosensory organs well-developed on basis of bioassays where?
capabilities?
certainly used in intra-specific activity
probably used in navigation
use in predatory activity probable

45. Booklungs
derived from bookgills by invagination
structure
operation

46. Spinnerets
silk spinning organs are located on the ventral surface just anterior to the terminal anus.
in Mygalomorphae they are obviously segmented and may be long and very mobile.
Mygalomorphs mostly have 4 spinnerets, Hexathelidae have 6.

47. Silk! silk the key to understanding spiders
use of silk opened up new niches
most important ecological aspect is silk allowed access to flying insects - a large resource mostly not available to other organisms
a ‘new zone of adaptive radiation’

48. Functions of silk include:
1. Draglines - common to most spiders (= lifeline)
2. Sperm webs
3. Nest building - retreats (overnight and overwintering)
4. Egg cocoons - wrapping eggs
5. Locomotion aids:
Ballooning strands - dispersal of spiderlings Bridge building (adults)
6. Sensory extensions - trip-lines, ‘microphones’
7. Web building - prey capture
8. Swathing prey - to immobilize or keep in web.
9. Mating aids (mating webs/constraining mate)

49. Silk glands 9 kinds recognised
derived from excretory glands associated with appendages on ancestral ‘abdomen’
protein produced as aqueous solution
solidifies on being stretched (thixotrophic)

50. Nephila silk glands
1. piriform 2. aciniform 3. ampullate 4. aggregate 5. flagelliform 6. cylindrical and 3 other types
that female Nephila don’t have!

51. Silks many kinds of silk all kinds not present in every spider
structural silks
draglines, retreats, egg-cocoons, ...
prey-catching silks
cribellate
ecribellate

52. Physiology haemolymph circulation respiration digestion excretion
nervous system

53. Heart and circulation
tube in dorsal opisthosoma … ‘ostia’ (valves) enables haemolymph to enter from pericardiac sinus, pumps forward to prosoma
haemolymph provides working fluid for hydraulic system
haemolymph clots very quickly to seal any leaks

54. Respiration
oxygen is dissolved in the haemolymph as it passes through the booklungs
most (not all) spiders have haemocyanin which binds oxygen
oxygen transported by blood flow
very low resting metabolic rate

55. Digestion extra-oral predigestion sucking pharynx
digestion in midgut and diverticulae (= caecae)
secretions of coxal glands run forward in channels and contribute to extra-oral processing

56. Excretion Malpighian tubules guanine main nitrogenous waste
also uric acid

57. Nervous system concentrated on prosoma
exceptionally large for size of animal (general feature of arachnids)

58. Reproduction mating - indirect insemination females store sperm
mating systems
courtship
copulation
cannibalism …
other features
maternal care

59. Prey handling varies, often specialised
species with paraxial fangs run over their prey and stab downwards, often pinning the prey to the ground in the process.**** Bjorn challenges ****
silk-throwing
ambush

60. Venom
poison glands in the basal segments of the chelicerae and head open at the tip of the fang
poison is released from the gland by contraction of muscle surrounding the gland.
spider can control which components are injected

61. Toxicity!
spider venoms are complex and often contain rapid acting short term 'knock out' components and/or proteolytic enzymes.

62. Latrodectus - black-widow, red-back etc, etc (species complex - world wide) LV1 - insects, knockdown, reversable LV2 - insects, slow, irreversable LV3 - vertebrates only, causes pain
Atrax - intensively investigated … composition complex - within a species varies with age, sex, locality, season and hunger level! Presume same in other mygalomorphs

63. Humans ...
Atrax robustus male - usually dry-bites! 14 deaths
Shortest 8 minutes! 5 < 2h.
antivenom developed 1980.
some Hadronyche species probably considerably more poisonous!
Latrodectus, Loxosceles … others

64. Feeding
normal method: crush, slobber and suck – extra-oral digestion, suck in fluids.
vs Thomisidae
liquids and small particles only - via ‘pumping pharynx’ (‘pumping stomach’)

65. Prey some spider species are prey specialists,
others are extremely general, attacking as opportunity arises.

66. Webs ? derived from safety lines or sensory lines many different kinds
some detain prey briefly other kinds hold prey firmly
cribellate silk (‘velcro’)
ecribellate sticky silk (‘glue’)

67. cribellate silk ecribellate silk
tufts of very fine silk added to main thread
tangle setae, protuberances - gets insects
remains ‘sticky’ for a long time
has evolved in several lineages
ecribellate silk
sticks through proteinaceous glue
glue added as silk spins
glue droplets produced by ‘strumming’
stickiness deteriorates rapidly

70. Web structures sensory lines sheet webs orb webs cobwebs other webs
special webs - bolus spider, net-casting spider etc.

71. Vagrant and cursorial hunters
‘option’ occurs in many spider lineages
Salticidae (jumping spiders), Lycosidae (wolf spiders) best studied
very common, but mostly nocturnal so not widely observed

72. Salticidae largest (most speciose) family
characterised by eye structure and vision
stalk then leap onto prey

73. success of spiders
possibly most successful of the arachnids (mites challenge ...)
moderately speciose (substantially more species than the vertebrates)
can be VERY abundant (>106/ha found)
hooked into insects as a resource
considerable diversity - many niches

74. web exercise
find out about the morphology and likely ecology of triginotarbid arachnids