Ricinulei
Group represented: Neoricinuleids
Forwarded cucullus hiding the chelicerae
2-segmented small chelicerae
Carapace densely granulated
Males’ 2° femur enlarged
Double trochanter (3° & 4° pairs of walking legs)
Complex dorsal lock between the prosoma & the narrowed 1° opisthosomal segment
Trilobed opisthosoma with Lateral Lobe/Plate & Median Lobe/Plate
Last 3 segments of the opisthosoma form a short postabdomen
Pedipalps ending with a small pincer claw
Males’ 3° legs modified for reproduction
Tracheal openings hidden among the legs
Pedipalp folded under the body & ending with a pincer claw
Phalangiotarbida
Genus represented: Mesotarbus
Small leg-like pedipalps
Extremely small chelicerae, exact morphology unsure
6 eyes arranged in 3 pairs on a trifoliate tubercle
First 6 segments of the opisthosoma are densely packed on the dorsal side
Broad 3-segment end of opisthosoma (often fused)
Dorsal anal opening
Ogive-shaped main body
Crab-like heavy walking legs
1 pair of spiracled linked to unknown respiratory organs
reproductive’s morphology unknown
Note: This group is still poorly known; further research could change several details radically.
Pseudoscorpiones
Group represented: Cheliferoids
Pedipalps turned into pincer claws (with venomous glands in iocheirates species)
Small 2-segmented chelicerae with a small spinneret called “galea” on the moveable digit linked to a silk gland
0 to 4 simple eyes on the forward rims of prosoma
Patella usually is longer than the femur
Exoskeleton can be heavily ornamented with tubercles
Opisthosoma ending by an anal cone, no telson
2 pairs of tracheae
Large genital plate
First opisthosomal segment non-visible on ventral side
Endite (extension of the pedipalp’ coxae to process food)
Scorpiones
Group represented: Orthosternians
Pedipalps turned into pincer claws
2 median eyes in & little lateral pairs
Legs telescoped backwards
Legs’ coxae well-developed & forming a stomotheca (a pre-oral chamber before the mouth)
Sternum
Genital opening & Pectines (ventral sensory appendages close to the ground) closely grouped
4 pairs of book lungs
Opisthosoma subdivided into a mesosoma of 7 segments & a metasoma (=”tail”) of 5 segments
Telson turned into a venomous sting
Acculeus (sting)
Vesicle (contains the venom)
Note: Scorpions changed a lot since the Silurian, many of the paleozoic species didn’t have stomotheca for example. This diagram is mostly representative of today’s species.
Orders of unclear affinities & scorpion-like figures: ricinulei, phalangiotarbida, pseudoscorpiones and scorpiones
#Cheliceratime #arachnid #ricinulei #phalangiotarbida #pseudoscorpion #scorpion
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