Monatractides oxystomus ( K. Viets, 1935 )

Pesic, Vladimir & Smit, Harry, 2009, Water mites of the family Torrenticolidae (Acari: Hydrachnidia) from Thailand, Part II. The genus Monatractides K. Viets, Zootaxa 2012, pp. 1-27 : 13-15

Monatractides oxystomus ( K. Viets, 1935)

( Figs. 53–62 )

Material. Thailand: Stream near Haewsai Waterfall, Nam Nao NP., 425 m asl, 16.xi.2007, 16° 40.668 N 101° 41.856 E, leg Smit 1/0/0 (0/1/0 mounted); stream downstream of Siriphum Waterfall, Doi Inthanon NP, 1300 m asl, 26.xi.2007, 18° 31.532 N 98° 39.091 E, leg. Smit 0/1/0 (0/1/0 mounted).

Morphology. Male: Idiosoma (ventral view: Fig. 54 ) L 750, W 681; dorsal shield ( Fig. 53 ) L 650, W 534, L/W ratio 1.2; dorsal plate L 588; shoulder plate L 208, W 78, L/W ratio 2.7; frontal plate L 116, W 81, L/W ratio 1.43; shoulder/frontal plate L ratio 1.8; capitular bay L 134, Cx-1 total L 265, Cx-1 medial L 131, Cx- 2+3 medial 91; ratio Cx-1 L/Cx-2+3 medial L 2.9; Cx-1 medial L/Cx-2+3 medial L 1.4; genital field L/W 144/120, L/W ratio 1.2, ejaculatory complex ( Fig. 57 ) L 213; distance genital field–excretory pore 135, genital field–caudal idiosoma margin 234; capitulum ( Fig. 56 ) ventral L 145; palp ( Figs. 58–59 ) total L 205, L and %L (given as % of total L): P-1 24 (11.7), P-2 55 (26.8), P-3 39 (19.0), P-4 58 (28.3), P-5 29 (14.2); P-2/ P-4 ratio 0.95; L-I-Leg-4-6: 100, 96, 93.

Female: Idiosoma (ventral view: Fig. 61 ) L 788, W 663; dorsal shield ( Fig. 60 ) L 713, W 572, L/W ratio 1.25; dorsal plate L 656; shoulder plate L 245, W 83, L/W ratio 2.95; frontal plate L 131, W 81, L/W ratio 1.6; shoulder/frontal plate L ratio 1.87; capitular bay L 139, Cx-1 total L 278, Cx-1 medial L 138, Cx-2+3 medial 83; ratio Cx-1 L/Cx-2+3 medial L 3.35; Cx-1 medial L/Cx-2+3 medial L 1.7; genital field L/W 184/166, L/W ratio 1.1; distance genital field–excretory pore 181, genital field–caudal idiosoma margin 228; capitulum ventral L 152, chelicera L 186; palp ( Fig. 62 ) total L 214, L and %L (given as % of total L): P-1 26 (12.1), P- 2 56 (26.2), P-3 41 (19.2), P-4 59 (27.6), P-5 32 (15.0); P-2/P-4 ratio 0.95; L I-Leg-4-6: 103, 97, 92.

Remarks. Due to the presence of three pairs of knob-shaped protrusions at the margin of the capitular bay, the presence of denticles on the distal margins of P-3, one very long ventral seta at P-4, a pointed, V-shaped capitular bay and the posterior medial region behind the genital field pointed, the specimen from Thailand shows a general conformity with the description given for M. oxystomus (see K. Viets 1935, Lundblad 1971). M. oxystomus closely resembles M. oza ( Cook, 1967) , a species known from India which differs in having slightly shorter and wider frontal platelets, but this character is known to be variable in this species (see Lundblad 1969). A further difference is found in the absence of denticles at the distal margins of P-2 and P-3 (see Cook, 1967: Fig. 244). The variability needs to be examined more to clarify the taxonomy.

Distribution. Indonesia. New for Thailand.

Figures

FIGURES 53 – 59. Monatractides oxystomus (K. Viets), male, Haewsai Waterfall: 53 = dorsal shield; 54 = idiosoma, ventral view; 55 = anterodorsal portion of ventral shield; 56 = capitulum; 57 = ejaculatory complex; 58 = palp (P- 1 missing), medial view; 59 = palp (P- 1 missing), lateral view. Scale Bars = 100 µm.

FIGURES 60 – 62. Monatractides oxystomus (K. Viets), female, stream downstream of Siriphum Waterfall: 60 = dorsal shield; 61 = idiosoma, ventral view; 62 = palp, medial view. Scale Bars = 100 µm.