Water mites from Fuerteventura, Canary Islands, Spain (Acari: Hydrachnidia) Author Smit, Harry Naturalis Biodiversity Center, P. O. Box 9517, 2300 RA Leiden, the Netherlands. harry.smit@naturalis.nl text Ecologica Montenegrina 2017 2017-06-27 11 14 19 journal article 10.37828/em.2017.11.4 2336-9744 13237322 urn:lsid:zoobank.org:pub:C9473F13-9463-4D2F-83BA-DB67DFFD95F2 Arrenurus (Micruracarus) caesaraugustanus Viets, 1930 Arrenurus pervius Walter, 1940 – New syn. ( Fig. 2 A-B) Material examined . 4/21/0, Temporary pool, Barranco de la Muley, 28º 25.161 N 13º 53.214 W , alt. 45 m asl, 2-iii-2017 . Description . Male: Idiosoma 894-965 long and 664-737 wide. Dorsal shield somewhat elongated, dorsal furrow in two males complete, in two other males (both fully sclerotized) incomplete (fig. 2A). Petiole hyaline, tube-like, dorsal margin with a broad tooth (fig. 2B). Female: The female matches the description given by Viets (1930) , but there is a remarkable range in size: length 794-1166, width 648-925. Remarks . Walter (1940) described A. pervius from Algeria , but his description matches the description of A. caesaraugustanus from Zaragoza Province, northern Spain given by Viets (1930) and he does not discuss diagnostic differences between the two species. The figure of the male posterior idiosoma of Walter is very sketchy, but in the description he mentioned the hyaline tube-like petiole with a small tooth in the middle of the dorsal margin (as given in Fig. 2B ). Moreover, the size of A. pervius is in agreement with A. caesaraugustanus : Male L 900, W 750, female L 1140, W 945. Palp measurements of Viets (1930) of A. caesaraugustanu s must be erroneous, as they are two times as large as the specimens from Fuerteventura. When we take this into consideration, palp measurents of the two species are similar. The only difference is the number of setae on the medial margin of P2, seven in A. caesaraugustanus and four in A. pervius . However, the female of A. caesaraugustanus has P2 with four setae only. Therefore I propose to synonymize A. pervius with A. caesaraugustanus . The species is known only from Spain , Algeria and Fuerteventura. All localities where the species has been found are either temporary or somewhat saline. Acknowledgement I am indebted to Truus van der Pal (Alkmaar) for her assistance with the field work.