Trigonotarbida
Forwarded clypeus hiding the chelicerae
2 median eyes & little pairs on the sides
Complex dorsal lock between the prosoma & the narrowed 1° opisthosomal segment
Last 10, 11 & 12 segments folded on the underside, the last to in a sort of “postabdomen”
Ventral sac
2 pairs of book lungs
3 claws:
2 large ones & a smaller one
Last segment of the chelicera turned into a fang
Trilobed opisthosoma with Lateral Lobe/Plate & Median Lobe/Plate
Araneae (spiders)
Group represented: Araneomorphs
Last segment of the chelicera turned into a venomous fang
Palpal bulbs for reproduction in males
Primitively 8 eyes in 2 rows, but eye pattern highly variable
Fovea
Patella often shorter than Femur & Tibia
No muscles to extend the legs, extension is done by self-regulation of internal hydraulic pressure
2 claws by default, 3 among web-spinning species
Opisthosoma often without external segmentation
2 to 6 spinnerets from which silk is spinned
Book lungs (1 pair in araneomorphs, 2 in tarantulas & mesotheles)
Tracheae (absent in tarantulas & mesotheles)
Epygine (female genital opening)
Narrow pedicel (“wasp waist”)
Sternum
Labium
Endite (extension of the pedipalp’ coxae to process food)
Notes: Spiders are highly diverse, this is an overall generalised body plan. Uraraneids and other stem spiders lineages are based on the same general model but with sometimes a flagellum and doubts about the presence of true spinnerets
Pedipalpi
(Vinegaroons, schizomids & amblypygids/”whip spiders”)
2 median eyes in & little lateral pairs for species with sight
Prosoma in one block for vinegaroons & amblypygids, subdivided like solifuges & palpigrades for schizomids
Last 3 segments of the opisthosoma are smaller & forming a postabdomen
Telson mondified into a flagellum (lost in amblypigids & reduced in schizomids)
2 pairs of book lungs (only one in schizomids)
Tarsus is always subdivided into tarsomeres
First pair of legs elongated and used as antennae, loss of their walking function
Large raptorial pedipalps
Note: This diagram is a mix of both schizomids, vinegaroons & amblypygids to show the numerous features shared by these 3 orders despite their differences.
And for the end of the thread, the pantetrapulmonates: trigonotarbida, araneae (spiders) and pedipalpi (vinegaroons, amblypygids, schizomids)
Thank you for reading & I’ll see you on the next #Cheliceratime!
#arachnid #spider #trigonotarbid #vinegaroon #amblypygid #schizomid
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