Atractides

Gerecke, Reinhard, 2003, Water mites of the genus Atractides Koch, 1837 (Acari: Parasitengona: Hygrobatidae) in the western Palaearctic region: a revision, Zoological Journal of the Linnean Society 138, pp. 141-378 : 251-252

ATRACTIDES LONGUS ( WALTER, 1947)

Megapus longus Walter, 1947

Syn. to A. oblongus ( Walter, 1944) : syn. nov.

Type series: Lectotype ♂, here designated: NHMB Megapus longus Walter ♂ Sorne 29.7.1944 Coll. Walter; Typus; Sorne ob. Undervelier N ∞60/1944 29.7.1944; XV/87. Pasted over: Megapus longus Walter [undecipherable] Pr. 1587 Typ ♂. State of conservation: perfect, Gsk in situ, right I-L and gnathosoma separate, lateral, one palp isolated lateral, precipitations in embedding fluid . Paralectotype ♂: NHMB DIII b. 51 g, Schweiz, Brülbach b. Brülisau 3.8.1945 Coll. Walter’. State of conservation: dorsum/ventrum separated, gnathosoma and both I-L separated lateral, one palp isolated, mounted in Hoyer’s fluid from vial material together with one undissected deutonymph (Gerecke) . Paralectotypes ♀: NHMB Megapus longus Walter ♀ Schwendebach 3.8.1945 Coll. Walter; Typus; Schwendebach ob E. W. Wasserauen 3.8.1945; XVI/32. Pasted over: Megapus longus Walter D. 6 B 51 Pr. 1632 Typ ♀. State of conservation: good, right I-L and III-L and gnathosoma (incl. chelicerae) separate lateral, both palps isolated, in oblique position (measuring impossible) no precipitations; NHMB DIII b.51 f, Schweiz, r. Zufl. d. Brülbach, 3.8.1945 Coll. Walter. State of conservation: dorsum/ventrum separated, gnathosoma and both I-L separated, palps and chelicerae (with claws remaining in the gnathosoma) isolated, mounted in Hoyer’s fluid from vial material (Gerecke) .

Description: see under A. oblongus ( Walter, 1944) .

Discussion: As often found in Walter’s descriptions, measurements are out by c. 10–20%. Both males are obviously juveniles (weak sclerotization, perhaps also the name-giving slender idiosomal shape, straight caudal margin of Cx-4 with an abrupt mediocaudal angle; in one specimen palps damaged with crushed P-4). Walter compared A. longus to A. subterraneus , a species similar in having a slightly modified shape of I-L-5 and -6, but with both sexes differing in the genital and postgenital field (with very small Ac, Vgl-1 separate from Vgl-2) and palp (with long, flattened dorsal setae on P-2/3, sword seta of P-4 near ventrodistal hair). Among the species with unsclerotized muscle attachments and Vgl-1 fused to Vgl-2, A. longus is very similar to A. spinipes and A. oblongus , but differs from A. fonticolus in the nonlineated integument, and from A. latipes in the slightly modified shape of I-L-5 and -6, with narrow setal interspace.

With regard to most measurements, males and females are within the range of variability of A. spinipes , and some of the minor differences could possibly be explained by the juvenile age of the members of the type series of A. longus : in males, the slightly more slender genital field (L/ W 0.82 –0.94, in A. spinipes 0.97–1.05) and in females the more slender coxal field (L/Cx-3 W 0.87 –0.91, in A. spinipes 0.76–0.86). The shape of I-L-5 and -6 of the two species is similar, with the only exception being the sword setae arranged still more closely together than in A. spinipes (interspace in females 9–12, in males 7–8 Mm; A. spinipes : females 12–16, males 8–10 Mm). Also in the mouthparts, only slight differences are found: the total L of the female palp remains below the minimum in A. spinipes , but in view of the extreme variation in palp length in males, this is a relatively insignificant character. In the measured female and two males of A. longus , P-2 is more slender than in A. spinipes (in the female also P-4), while this segment is rather stout in males. The L/H ratio of P-4 is, however, strongly influenced by probably artificial inflation of this segment, especially in juveniles. In both sexes a difference is found in the shape of the chelicera, with a basal segment/claw ratio of 2.51–2.70 (in A. spinipes 2.21–2.38). The most significant difference between these two similar species concerns the genital field of females: while the Ac of A. spinipes are arranged in a weakly curved line, with Ac-2 trapezoidal in shape, in A. longus they form an obtuse angle, and the Ac-2 is triangular in shape, with its medial point directed towards the gonopore. In males, a difference between the two species is found in the arrangement of Ac-3: in A. spinipes , their anterior margin lies in the posterior fifth of the gonopore, in A. longus , they are shifted anteriorly and flank the posterior third of the gonopore. Furthermore, the number of genital hairs flanking the gonopore is 4–5 pairs in A. longus , but 6–7 pairs in A. spinipes .

A genital field perfectly corresponding in shape and arrangement of Ac is found in the little known A. oblongus . If we compare the measurements of the females of A. longus with the holotype of A. oblongus , we find only minute differences: the palp is 15% longer, I-L-5 and -6 and P-2 and -3 are relatively thicker. Such differences in proportions are best explained as deformations, easily caused in slide mounted juveniles due to weak sclerotization. A. longus is therefore considered a synonym of A. oblongus , a species closely related to A. spinipes .