Sigthoria Koenike, 1907

Gerecke, Reinhard, 2004, The water mites of Madagascar (Acari, Hydrachnidia): a revised list completed by original material conserved at the Muséum national d’Histoire naturelle, Paris, Zoosystema 26 (3), pp. 393-418 : 399-400

Genus Sigthoria Koenike, 1907

Sigthoria nilotica ( Nordenskiöld, 1905) ( Figs 3 ; 4 )

Amasis niloticus Nordenskiöld, 1905: 9 , fig. 5a-b.

Sigthoria nilotica – Koenike 1907, 127.

MATERIAL EXAMINED. — Madagascar. Northwest; Sambirano; 1.

DISTRIBUTION. — Widely distributed in the tropics, but only rarely found, generally as single specimens only, recently detected also in The Netherlands, far outside the previously known distribution area ( Smit & Van der Hammen 1992).

DESCRIPTION

The female from Madagascar has the following measurements: idiosoma L/W 600/480, dorsal shield L/W 550/440; lateral eye distance (as measured between the median lenses) 155; distance between insertion points IV-L 350; IV-L segments 2-6 dorsal L 82, 90, 123, 147, 150; genital field L/W 145/130; chelicera basal segment L 190, claw L 70, maximum H 40; palp segments L/H P-1 25/35, P-2 90/60, P-3 55/45, P-4 112/30, P-5 25/12. Lateral eyes, together with the frontal glandularia, imbedded into the frontal part of the ventral shield (see Fig. 3C ). Dorsal shield ( Fig. 3A ) with a characteristic pattern of paired sulci and elevations; IV-L ( Fig. 4 D ) bearing some very long distal setae on segments 2-5, swimming hair numbers: IV-L-3 1; IV-L-4 2, IV-L-5 1; claws of this leg reduced to a pair of minute, peg-like setae. Ventral shield ( Fig. 3B ) with an extended postgenital area, excretory pore close to posterior margin; genital field with 16 pairs of minute acetabula; gnathosoma ( Fig. 4 A ) ventral margin with a well developed central hump the anterior part of which is concave; cheliceral basal segment distinctly enlarged near the claw insertion ( Fig. 4B ); palp ( Fig. 4C ) elongated, with rugose ventral surface of P-2 and P-4, ventral seta of P-2 tiny and curved.

DISCUSSION

Harvey (1990) found differences in the swimming hair equipment between populations from different areas in Australia and discussed the possible taxonomic significance of this character. However, from this point of view the specimen from Madagsacar agrees well with populations from Asia and continental Africa.

Family LIMNESIIDAE Thor, 1900

Figures

FIG. 3. — Sigthoria nilotica (Nordenskiöld, 1905),; A, dorsal shield; B, ventral shield; C, region of lateral eyes. Scale bar: 100 µm.

FIG. 4. — Sigthoria nilotica (Nordenskiöld, 1905),; A, gnathosoma in lateral view; B, chelicera; C, palp in lateral view; D, fourth leg. Scale bar: 100 µm.