Solifugid Relatives (Higher Level Relationships)
Solifugae relationships within the Arachnida based upon Morphology
Arachnid relationships have long been debated and many cladistic hypotheses have been proposed. Ordinal interrelationships have varied for decades, depending on data types and analytical approaches. Many morphological studies since the late 70s converged on Pseudoscorpiones being the sister group of Solifugae rather consistently based on a number of morphological characters (Shultz, 1990; Shultz, 2007; Weygoldt & Paulus, 1979; Wheeler & Hayashi, 1998). However, other morphological studies suggest that solifuges are most closely related to Acariformes due to the presence of a homologous sejugal furrow and similar sperm ultrastructure (Alberti & Peretti, 2002; Dunlop et al., 2012). Interestingly, Schultz (2007) also recovered a Solifugae and Acari clade at the beginning of his morphological analyses, yet all finalized analyses consistently supported a Solifugae + Pseudoscorpiones relationship.
Solifugae relationships within the Arachnida based upon
With the advent of sequencing technologies, researchers are able to accumulate data at a remarkable rate. Recent studies using molecular sequence data have provided researchers another approach for resolving arachnid relationships, yet many analytical approaches using “big data” are available, which has reflected inconsistent results among major arachnid groups. While Lozano-Fernandez et al. (2019) support a Solifugae + Pseudoscorpiones grouping using molecular data, many other researchers reject the classical Solifugae + Pseudoscorpiones grouping based on morphology and support a Solifugae + Ricinulei relationship (Regier et al., 2010; Sharma et al. 2014; Ballesteros & Sharma, 2019, Noah et al., 2020). Historically, solifuges have lacked detailed phylogenetic attention. The few phylogenetic studies have focused on the family Eremobatidae using a multilocus approach (Cushing et al. 2015) and on the family level using Cytochrome c Oxidase I (COI; Maddahi et al. 2016). Understanding the evolutionary relationship of Solifugae within Arachnida is important for helping to resolve the interrelationships of the Order. Ultimately, a phylogenetic framework could help guide future taxonomic revisions in this fascinating group of arachnids.
Representatives of different arachnid orders. Top left: Order Thelyphonida (whipscorpion); Top right: Order Amblypygi (tailless whip scorpion); Middle left: Order Scorpiones (scorpion); Middle right: Order Araneae (spider); Lower left: Order Opiliones (harvestman); Lower right: Order Acari (mite).