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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