Decussobates minutipalpis, Smit, 2018

Smit, Harry, 2018, A new species of the genus Decussobates Cook, 1988 from Argentina, with the first description of the male (Acari: Hydrachnidia: Hygrobatidae), Zootaxa 4471 (1), pp. 182-184 : 182-184

Decussobates minutipalpis n. sp. ( Figs. 1A–G )

Material examined. Holotype male, Rio Pipo, a relatively large, fast flowing stream with a gravel bottom, Tierra del Fuego NP, Tierra del Fuego, Argentina, 56 ° 49.101 S 68 ° 28.314 W, alt. 96 m a.s.l., 27-ii- 2018 ( MBR) . Paratypes: one female ( MBR), one male, one female ( RMNH), same data as holotype .

Description. Eyes present but small. Dorsal furrow with three pairs of glandularia. Gnathosoma fused with Cx-I, the latter fused medially, tip of Cx-I with several long setae. Between insertions of fourth legs and genital field one pair of glandularia. A pair of large glandularia flanking the genital field. Palp stocky, especially P-4. Legs without swimming setae. I-leg-5 without a curved distal seta.

Male: Idiosoma dorsally 624 (616) long and 437 (462) wide, ventrally 664 (664) long. Dorsal shield 567 (559) long and 356 (389) wide, bearing the postocularia and three pairs of glandularia. Ventral shield present. All suture lines of coxae incomplete. Glandularia of Cx-IV near suture line between Cx-III and Cx-IV. Genital field with five pairs of glandularia, two pairs located anteriorly and two pairs located posteriorly, in between these two pairs one larger pair of glandularia. Length of P-1-5: 16, 52, 24, 34, 38. P-2 with a large ventral projection with a pointed anteroventral extension. P-4 ventrally with several thin setae, one of which is much longer the other two setae. P-5 elongated. Length of I-leg-4–6: 82, 84, 70. Length of IV-leg-4–6: 110, 100, 80. Excretory pore located near ventral idiosoma margin.

Female: Idiosoma dorsally 721 (697) long and 510 (470) wide, ventrally 770 (753) long. Dorsum with three large plates, posterior plate 359 long and 365 wide. Anterior dorsal plate flanked by two small platelets, each with two glandularia. Anterior plate with the postocularia, middle plate without glandularia and posterior plate with two pairs of glandularia. Dorsal furrow with three pairs of glandularia. Posteriorly to posterior margin of Cx-IV a large area of secondary sclerotization. Genital field 188 wide, with 6–7 (8–9) pairs of acetabula. Pregenital sclerite large, 102 wide. Postgenital sclerite small and narrow, near posterior idiosoma margin. Length of P1-5: 28, 58, 34, 35, 38. Length of I-leg- 4–6: 82, 90, 81. Length of IV-leg-4–6: 126, 122, 104. Excretory pore near posterior end of dorsum.

Etymology. Named for the very small palp.

Remarks. The new species differs from the two known species, i.e. Decussobates planus Cook, 1988 and D. angustus Cook, 1988 in the lower number of acetabula of the female (6–9 pairs versus 11–12 pairs) and the smooth margin of the projection of P-2 (serrated in the two known species). According to Cook (1988) the genus Decussobates shows affinities with Szalayella Lundblad. Now that the male of Decussobates is known, this can be confirmed. In both genera males have one large dorsal plate, while the females have several large dorsal plates.

Figures

FIGURE 1. Decussobates minutipalpis n. sp. A–E holotype male, F–G paratype female. A = dorsum; B = venter; C = palp lateral; D = palp medial; E = I-leg-4–6; F = dorsum; G = venter. All scale bars = 50 µm.