Atractides (Tympanomegapus) pavesii Maglio, 1905

Gerecke, Reinhard, 2021, The water mites of the family Hygrobatidae (Acari, Hydrachnidia) in Italy, Zootaxa 5009 (1), pp. 1-85 : 44-45

Atractides (Tympanomegapus) pavesii Maglio, 1905

(Fig. 25 C)

Material examined: Lazio: I 880, 0/1/0, slide; I 1287, 0/3/0 (0/1/0 slide).

Previously published records from Italy: Abruzzo (K. Viets 1955, Cicolani & Di Sabatino 1985; Lombardia ( Maglio 1905, 1906); Marche (K. Viets 1955); Piemonte ( Ramazzotti 1947, Nocentini 1960, 1963).

Habitat: Rhithrobiont. Medium order streams with not too turbulent flow, at low altitudes, 115-200 m.

Distribution: Europe, scattered records.

Genus Hygrobates Koch, 1837

Diagnosis: Except for the coxal field, idiosoma in all Italian species covered by membranous integument. Coxal field fused with the gnathosomal base to form a large anteroventral plate, with sutures Cx-I/gnathosoma remaining visible in anterior part as a pair of characteristic, parallel or slightly converging lines. Glandular opening on Cx- IV in Italian species near suture line Cx-III/IV. No sclerotized frontal lamella dorsal to the gnathosoma insertion. I-L-5/ 6 in shape and setation not remarkably differing from distal segments of other legs (distal setae on I-L-5 not modified). Genital field with three to numerous pairs of acetabula. Male gonopore completely surrounded by genital plate, female gonopore flanked by paired genital plates. P-2 with or without ventral projection; P-2 and P-3 with denticulate ventral margin; P-4 not bearing a medial sword seta, its dorsodistal surface not densely covered by fine setae.

Discussion: Due to the characteristic shape of the ventral shield with the incomplete suture lines Cx-I/ gnathosoma, species of the genus are highly characteristic in comparison to all other Italian water mite taxa except for Mixobates . The latter differs in the pair of glandularia perforating Cx-IV in full centre, and a pair of little conspicuous, but obviously modified distoventral setae on I-L-5.

Subgenus Hygrobates s. str.

Diagnosis: Genital field with three pairs of acetabula. Female gonopore flanked by a pair (in some extra-European taxa two pairs) of genital plates. Ventral margin P-2 with or without a distal projection.

Discussion: While in tropical areas several taxa are present that blur taxonomic differences, the attribution of adults of species from the investigated area to this or the alternative subgenus Rivobates (see below) is unproblematic. In contrast, no diagnostic differences are known for deutonymphs. In cases they have a characteristically structured integument, representatives of the latter stage can be recognized as belonging to the subgenus s.str. (and tentatively attributed to coexisting adults with the same integument structure). Instead, subgenus or species attribution is impossible for deutonymphs with a smooth integument.

Fig. 21: Hygrobatidae , integument structures. A, Hygrobates calliger , dorsum with lineation; B, Hygrobates fluviatilis , reticulated; C, Hygrobates cf. turcicus , reticulated with inner meshes; D, Atractides walteri , papillate.