Arrenurus (Megaluracarus) kostkai, Smit, Harry, 2010

Smit, Harry, 2010, Two new species of the genus Arrenurus from Pohnpei, Federal States of Micronesia (Acari: Hydrachnidia: Arrenuridae), Zootaxa 2606, pp. 50-54 : 51-54

Arrenurus (Megaluracarus) kostkai n. sp.

( Fig. 5–9 )

Material examined. Holotype male, Nan Pad stream, Pohnpei, Federal States of Micronesia, alt. 590 a.s.l., 30 June 2008 ( ZMAN). Paratypes: one male, 2 females ( BPBM), 1 female ( ZMAN), same data as holotype; one male, one female, Nan Pad stream, Pohnpei, Federal States of Micronesia, alt. 590, 30 January 2009 ( ZMAN); one female, same location, 1 July 2008 ( ZMAN); one female, Male Komea stream, Pohnpei, Federal States of Micronesia, 523 m a.s.l., 17 February 2009 ( BPBM); one female, Nan Moatoh stream, Pohnpei, Federal States of Micronesia, alt. 600 m a.s.l., 17 February 2009 ( BPBM); one female, Salapwuk #2 Sakau stream, Pohnpei, Federal States of Micronesia, alt. 545 m a.s.l., 12 February 2009 ( ZMAN).

Diagnosis. D3 of male on large humps, cauda posteriorly with a narrow median cleft, posterior margin of cauda slightly indented; female with straight and obliquely directed narrow genital plates and without swimming setae.

Description. Male: Idiosoma 907 (915–956) long and 543 (502–526) wide, anterior idiosoma margin straight. The colour cannot be ascertained as the specimen has been fixed in ethanol. Dorsal shield complete, 478 long and 381 wide, D3 on large humps. Cauda distinctly set off from anterior idiosoma, posteriorly with a median cleft, posterior cauda margin slightly indented, D4 on humps. Anteriorly of median cleft an area without body pores. Due to fixation in ethanol some structures (glandularia, setae) are not well visible as the holotype is very dark. Therefore, in lateral view only the outline of the idisoma is illustrated. Gonopore 57 long, genital plates extending to lateral idiosoma margin and there widened and swollen and therefore visible in dorsal view. Lengths of PI-PV: 38, 78, 50, 76, 32; PII medially with two setae. Lengths of I-leg-4–6: 136, 148, 114. Lengths of IV-leg-4–6: 259, 164, 120; IV-leg-4 without a spur. Third and fourth legs with numerous swimming setae.

Female: Idiosoma 656 (616–697) long and 555 (551–599) wide, truncated posteriorly with distinct posterolateral corners. Anterior idiosoma margin slightly convex. Dorsal shield complete, 575 (512–615) long and 462 (429–478) wide. First coxal plates extending beyond anterior idiosoma margin. Medial margin of third coxae shorter than medial margin of fourth coxae. Medial distance of fourth coxae shorter than width of one genital valve. Gonopore 120 long and 154 wide, genital valves without sclerotization but gonopore of one female with triangular anterior and posterior sclerotized patches. Genital field 478 wide, genital plates straight, narrow and obliquely directed. Lengths of PI-PV: 28, 68, 60, 96, 52; PII medially with 2–3 setae. Lengths of I-leg-4–6: 122, 118, 94. Lengths of IV-leg-4–6: 140, 166, 164. All legs without swimming setae.

Etymology. Named in honor of Willy Kostka, currently the executive director of The Micronesian Conservation Trust. Mr. Kostka has played an important role in the conservation and preservation of terrestrial and aquatic ecosystems in Pohnpei and throughout all of Micronesia.

Remarks. The male of the new species is close to A. dahli Piersig from New Britain ( Papua New Guinea), New Caledonia and the Aru and Buru Islands ( Indonesia). This species also has the cauda with a median cleft, D3 and D4 on humps and swollen genital plates. The shape of the posterior margin, however, is different: the posterior margin is oblique without indentation. The absence of swimming setae in the female is unusual, especially as the male does have swimming setae.

Figures

FIGURES 5 – 9. Arrenurus kostkai n. sp. (figures 5 – 8 holotype male, figure 9 paratype female): 5 = dorsal view; 6 = ventral view; 7 = lateral view; 8 = palp; 9 = ventral view. Scale bars: 5 – 7,9 = 200 µm; 8 = 50 µm.