Omartacarus tucumanensis Fernández 1988

Fernández, Hugo R., 2002, Interstitial water mites of Argentina: Omartacarus Cook (Omartacaridae) and Meramecia Cook (Limnesiidae) (Acari: Hydrachnidia), Zootaxa 73, pp. 1-6 : 2-4

Omartacarus tucumanensis Fernández 1988

Male: Body soft and elongated. Length of body 770 colorless, coxal area typical of the genus ( Fig. 1 ), suture between first and second coxae incomplete, length between anterior end of first coxae and posterior end of fourth coxae, 255 medial separation of first and fourth coxae 171. Capitulum ( Fig. 2 ) 140 in length, rostrum gradually tapering anteriorly and without distinct annulations. Genital field ( Fig. 3 ) 115 in length and 59 in width Gonopore 38 in length and located near posterior end of genital field, genital acetabula 10 on each side. Dorsal lengths of the palpal segments ( Fig. 4 ): P­I, 14 P­II, 56 P­III, 24 P­IV, 45 P­V, 31 P­ bearing two medial setae expanded ( Fig. 4 ), P­III bearing two long distodorsal setae, P­IV with a ventral setal tubercle bearing a long curved seta and a big peg­like seta. P­V with four structures like a crown, tapering distally. Dorsal lengths of the distal segments of the first leg ( Fig. 5 ): I­Leg­4, 150; I­Leg­5, 91; I­Leg­ 6, 73. A few long, thin setae present but no true swimming hairs. Dorsal lengths of the distal segments of the fourth leg: IV­Leg­4, 180 V­Leg­5, 140 IV­Leg­6, 175

Specimens examined: Argentina; Tucuman province. Departamento Burruyacu, Medina Hills, Medina river (Type locality), 785 m above sea level (= masl) (27º 01’ S; 65º 04’ W); 1 male ( A05016 IML), 31 July 1984. Affluent Medina River 1 female ( A21007 IML), 20 October 1986; San Javier Hills, Cañas River 750 masl (26 º 48’ S; 65º 20’ W IML); 1 female ( A25009 IML) 19 February 1987. Salta province. Departamento Metan, Piedras River 820 masl (25º 30’ S; 64º 58’ W); 1 female ( A29300 IML), 18 July 1996. La Rioja, Departamento Valle Fertil, Potreros River (30º 37’ S; 67º 32’ W) 4 female ( A13002 ­ 005 IML), in leg. L. Grosso, 5 October 1981.

Discussion: The male described above occurred in the same collection as an O. tucumanensis female. However, I had initially assigned the specimen to O. brevipalpis , with some doubt. Years later (February 1994) D.R. Cook called my attention to several differences between O. brevipalpis and the Argentine exemplar. Then I reanalyzed the information about Omartacarus obtained to the present, distribution data, and observed frequency of females in other collections (Fernández unpublished data). After these studies I decided to re­identify this male specimen as O. tucumanensis . This decision is also supported by its occurrence near the type specimen’s locality; the differences from the female O. tucumanensis can be attributed to sexual dimorphism. The characters present in O. tucumanensis females (capitulum rostrum and P­IV peg­like seta), which we can attribute to a neotenic retention of some nymphal characteristics, are remarkable. Conversely, Cook (1980) observed that some nymphs of Omartacarus have a well­developed ejaculatory complex without a gonopore. I also tentatively assign the nymph collected by Cook (1980) from Tucuman province to O. tucumanensis . It was collected 8 km southern of O. tucumanensis type locality.

Omartacarus tucumanensis differs from O. brevipalpis by lacking the P­II distoventral projection, having P­II medial setae expanded and the ventral setal tubercle and associated curved seta smaller, and having fewer genital acetabula (16­18 in O. brevipalpis ).

Figures

FIGURES 1 ­ 5. Omartacarus tucumanensis, male. fig. 1: ventral view coxal plates; fig. 2: lateral view of capitulum, fig. 3: genital field; fig. 4: lateral view of palp and setae detail; fig. 5: distal segments first leg.