Kinematics of whip spider pedipalps: a 3D comparative morpho‐functional approach

Abstract

Amblypygi are tropical and subtropical ambush predators that use elongated, raptorial pedipalps for different activities. Although pedipalp use in predation and courtship has been explored in videography in vivo analyses, kinematic ex vivo examination of these appendages has not been conducted. Here, we rectify this lack of data by using micro‐CT scans to 3D‐kinematically model the appendage morphology and the range of motion (ROM) of the joints for Damon medius and Heterophrynus elaphus. We illustrate the successful application of this technique to terrestrial euarthropods in determining the maximum ROM values for each pedipalp joint. We also note that, in life, these values would be lower due to motion restricting structures like tendons, arthrodial membranes, and muscles. We further compare our maximum values obtained here with data from video‐based motion analyses. The ROM of each joint shows the greatest flexibility in the femur‐tibia joint (140–150°), the lowest in the basitarsus‐claw joint (35–40°). ROM in the tibia‐basitarsus joint is markedly distinct (D. medius: 44°; H. elaphus: 105°). This disparity reflects how H. elaphus uses the joint in the capture basket, while D. medius uses the femur‐tibia joint to form the capture basket. We further illustrate notable vertical motion of the H. elaphus pedipalp compared to D. medius. This difference reflects the retro‐ventral trochanter apophysis of H. elaphus. Our study opens the possibility to further whip spider kinematic understanding. Examination of other taxa using this approach will result in a more comprehensive understanding of the ecological significance and ethological implications of this unique arachnid group.

Spines and baskets in apex predatory sea scorpions uncover unique feeding strategies using 3D-kinematics

“…Furthermore, the motion of distal podomeres was comparable in both sea scorpions and whip spiders. However, overall eurypterids possibly had lower range of motion at joint 3 than whip spiders (also see Schmidt et al., 2021b ; Figures S7 and S8 in this publication).…”

“…Whip spider specimens from Damon medius and Heterophrynus elaphus were recently analyzed ( Schmidt et al., 2021b ). The specimens were scanned with a Phoenix Nanotom microcomputed tomography scanner housed at the Bavarian State Collection of Zoology using the following scanning parameters: 90 kV,110 mA, 2359 TIFFs, voxel size 15.…”

“…The maximum excursion angle measurement of each joint, ROM, was performed in Autodesk Maya 2021. We refer to this as range of motion (ROM) solely (compare Schmidt et al., 2021b ). However, when obtaining data on maximum excursion angles in each joint and the total scope of possible movements regarding a Cartesian coordinate system, we usually differ between single range of motion (sROM) and total range of motion (tROM; see Schmidt et al, 2020 , our Table S2 ).…”

Systematic Revision of the Whip Spider Family Paracharontidae (Arachnida: Amblypygi) with Description of a New Troglobitic Genus and Species from Colombia

“…1C, D, 2A–F; Beron, 2018: 95, 469, 682, table 8.4; McArthur et al, 2018: 62; Miranda et al, 2018a: 24; 2018b: 35, figs. 14, 15A; Miranda and Reboleira, 2019: 9; Nadein and Perkovsky, 2019: 603; Deharveng and Bedos, 2019: 125; Haug and Haug, 2021: 406–409, table 1; Schmidt et al, 2022: 164; Miranda et al, 2022: 161.…”

Variations in the carapace shape of whip spiders (Arachnida: Amblypygi)

“…Their first pair of walking legs are elongated (antenniform leg) and has a sensory role. Their spined pedipalps are used as raptorial legs for collecting small invertebrates and vertebrates (Ladle, 2009; Schmidt et al, 2021; Seiter et al, 2019). Whip spiders can live up to 10–15 years and are the only arachnids where both sexes moult throughout their entire lifetime.…”