Arrenurus rotundus ( Daday, 1905 )

Smit, Harry, 2020, New records of the water mite genus Arrenurus Dugès, 1834 from South America (Acari: Hydrachnidia: Arrenuridae), with the description of five new species and one new subspecies, Acarologia 60 (2), pp. 371-389 : 374

Arrenurus rotundus ( Daday, 1905)

( Figure 2 )

Material examined— Surinam. 12/9/0, ditch along Weg naar de Peperpot, 5°46.857 N 55°08.327 W, alt. 3 m asl, 18-xi-2019. Argentina. Entre Ríos Province: 0/2/0, ditch at Brazo Largo, N of Zarate, 33°54’37,21” S, 58°51’9,24” W, 6-xi-1999.

Description — Male: Idiosoma dorsally 360 long and 300 wide, ventrally 373 long. Gnathosomal bay shallow. Dorsal shield incomplete, 247 wide; distance dorsal shield – anterior idiosoma margin 48. Dorsum posterolaterally with small, rounded extensions. Cauda very short, not set off from anterior part of idiosoma; one pair of glandularia on cauda with short, forked setae. Medial margins of fourth coxae reduced to angles. Gonopore 28 long; genital plates long, extending to lateral idiosoma margin. Posterior to genital plates a pair of glandularia. Lengths of P1-5: 20, 64, 40, 64, 24. Palp rotated, P2 with two setae near ventral margin, P4 with a stout ventral seta ending in a hook-like tip. Length of I-leg-4-6: 60, 70, 80. Length of IV-leg-4-6: 74, 84, 86.

Remarks — According to Lundblad (1930), who examined the types A of. minimus ( Daday, 1905 ) and A. rotundus ( Daday, 1905) , the two species can be separated based on the pair of glandularia anterior and posterior of the genital plates. In minimus the anterior pair is more separated than the posterior pair, in the rotundus it’s the other way around. In my collection from Surinam, the Dadayella females show a large variation in the distance of these pairs of glandularia. In my opinion this characteristic is not suitable for species delimitation. The holotype of A. rotundus is lodged in the Naturhistorisches Museum in Basel, but unfortunately the slide does not contain the specimen (Hänggi pers. comm.). Daday’s (1905) illustrations are too sketchy or even erroneous to draw any conclusions. K. Viets (1954b) came to the same conclusion as Lundblad (1930) about the glandularia anterior and posterior to the genital plates. According to Viets (1954b) the palp of A. minimus has P5 with a distinctly downturned claw and the ventral seta of P4 is without a hook, while the palp A of. rotundus has the claw of P5 more obliquely orientated and the ventral seta of P4 is with a hook. Based on these differences it is clear that my specimens from Surinam belong to A. rotundus .

Rosso de Ferradas (1981a) reported A. nanus from Argentina, but according to Cramer & Cook (1992) the males must be assigned to A. rotundus . However, the males reported by Rosso de Ferradas (1981a) have a different configuration of the dorsal glandularia and setae (e.g. postocularia much closer to each other), differently shaped genital plates and antagonistic bristle without a hook, therefore they might belong to a different species. Unfortunately, I have not been able to examine these specimens.

Distribution — Known from Paraguay ( Daday 1905, Rosso de Ferradás & Böttger 1997), Brazil (K. Viets 1954a, b) and Argentina ( Rosso de Ferradas 1981a).

Figures

Figure 2 Arrenurus rotundus (Daday), male. A – dorsum; B – venter; C – palp; D – palp. Arrenurus minimus (Daday), female, Rio Cuminá, Brazil, slide 7343 Viets coll. (slide 43137 SMF). E – palp. Scale bars: A, B = 100 µm, C-E = 50 µm.