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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