Thinoseius variabilis, Halliday, 2010

Halliday, R. B., 2010, Revision of the Australian Eviphididae (Acari: Mesostigmata) 2596, Zootaxa 2596 (1), pp. 1-60 : 51-54

Thinoseius variabilis sp. nov.

( Figs 104–109 )

Material examined. Holotype. Female. New South Wales. Malonys Beach, near Batemans Bay , 35°43'S 150°11'E, 7 May 2008, R. B. Halliday coll., seaweed on beach . Paratypes. New South Wales. 13 females, same data as holotype . South Australia. 2 females, Nora Creina Bay , 37°20'S 139°51'E, 26 March 2008, R. B. Halliday coll., seaweed on beach . Victoria. 18 females, Mallacoota, Betka Beach , 37°34'S 149°45'E, 4 August 2007, J. Błoszyk and S. Konwerski coll., seaweed on beach ; 38 females, Mallacoota, Bastion Point , 37°34'S 149°46'E, 4 August 2007, J. Błoszyk and S. Konwerski coll., seaweed on beach (in ANIC) .

Description. Female. Dorsal idiosoma ( Fig. 104 ). Dorsal shield length 421–463 µm, width 245–276 µm (n=5), not completely covering dorsal idiosoma, surrounded laterally and posteriorly by unsclerotised striated skin. Shield with 17 pairs of setae and ca. ten pairs of pores, surface with delicate polygonal ornamentation throughout, indistinct medially. Setae z 1 minute, j 5, J 2, J 5 fine and needle-like, j 1 lanceolate, others slightly thicker, increasing in length posteriorly from j 2, 10 µm to J 3, 20 µm. Podonotal setae s 2, s 5, s 6, r 2, r 3, r 5, and opisthonotal setae Z 3, Z 4, Z 5, S 1, S 3, S 4, S 5 inserted in soft skin outside shield, all short, thick, spine-like.

Ventral idiosoma ( Fig. 105 ). Tritosternum with trapezoidal base and delicate finely pilose laciniae. Sternal shield reduced to a small sclerotised fragment bearing setae st 1 and lyrifissures stp 1, this shield fragment variable in size and shape, sometimes divided into two fragments each with one seta and one lyrifissure ( Fig. 106 ). Sternal setae st 2 and st 3, metasternal setae st 4, lyrifissures stp 2 and circular metasternal pore inserted in unsclerotised skin. Endopodal plates I–II, II–III and III–IV triangular, free, not fused with sternal shield fragments. Epigynal shield with concave lateral margins and convex posterior margin, weakly sclerotised, with indistinct longitudinal lines of ornamentation, epigynal setae inserted in soft skin outside shield. Anal shield oval, wider than long, surface smooth, cribrum long and narrow, post-anal seta more than double length of para-anal setae. Soft opisthogastric skin with six pairs of setae, two posterior pairs thick and spine-like, other four pairs very short and fine. Exopodal plates absent, metapodal plates small, kidney-shaped. Peritrematal shields narrow, with a conspicuous pore on outer margin of shield at level of coxa III, post-stigmatal section short, triangular, with a single post-stigmatal pore. Peritremes extending from stigmata at anterior level of coxae IV to anterior of coxae I.

Gnathosoma . Surface of hypostome with two rows of square markings flanking deutosternal groove. Rostral setae h 1 and interior setae h 3 subequal in length, 60 µm, exterior setae h 2 shorter, 40 µm, palp coxal setae shortest, 30 µm, all fine and needle-like ( Fig. 107 ). Deutosternal groove wide, margins slightly irregular, with five transverse rows of denticles, ca. eight denticles per row, and a smooth curved anterior line; corniculi robust, outer margin slightly indented, internal malae finely fringed. Setae av and pv on palp trochanter subequal in length, av thicker than pv; al on palp femur, genu and tibia shorter and thicker than pl, tarsus without long sensory setae, palp tarsal claw with two subequal spatulate tines. Epistome with five to eight anterior points, central point longest, central point and lateral points variable in length, width, and degree of distal subdivision ( Fig. 108 ). Fixed digit of chelicera with three triangular distal teeth and a basal ridge, pilus dentilis minute, dorsal seta short, erect ( Fig. 109 ); movable digit with two subequal distal teeth, arthrodial membrane a small rounded flap.

Legs. Chaetotaxy: Leg I. Coxa 0 0/1 0/1 0, trochanter 1 0/1 0/2 1, femur 2 3/1 2/2 2, genu 1 3/2 2/1 2, tibia 1 3/2 2/1 2. Leg II. Coxa 0 0/1 0/1 0, trochanter 1 0/1 0/2 1, femur 1 3/1 2/2 1, genu 1 3/1 2/1 2, tibia 1 2/1 2/1 2, tarsus 3 3/2 3/2 3 + mv, md. Leg III. Coxa 0 0/1 0/1 0, trochanter 1 0/1 0/2 1, femur 1 2/1 1/1 1, genu 1 2/12/ 0 1, tibia 1 1/1 2/1 1, tarsus 3 3/2 3/2 3 + mv, md. Leg IV. Coxa 0 0/0 0/1 0, trochanter 1 0/1 0/2 1, femur 1 2/1 1/0 1, genu 1 2/1 2/0 1, tibia 1 1/1 2/1 1, tarsus 3 3/2 3/2 3 + mv, md. All leg setae smooth and pointed, most dorsal setae thickened, ventral and lateral setae fine and needle-like. Pre-tarsi as for T. papillatus . Coxae I with two pairs of conspicuous coxal glands ( Fig. 105 ).

Genital structures. Insemination ducts arising from posterior margin of coxae III. Sacculus foeminus not visible in available specimens. Some specimens contain a single large spherical to oval egg, ca. 160 x 180 µm.

Etymology. The name T. variabilis refers to the variable form of the sternal shield of this species, which may consist of a single plate of variable shape and size, or may be partly or completely divided into two fragments.

Notes. Among the Australian species of Thinoseius , T. variabilis is distinguished from T. papillatus and T. peltatus by the fact that it has a normal anal shield bearing only three setae, surrounded by soft unsclerotised skin. This also distinguishes T. variabilis from T. ramsayi from New Zealand. Thinoseius variabilis is distinguished from T. helenae and T. jarretti by its very reduced sternal shield, represented by one or two very small sclerotised fragments between coxae I–II, with one pair of setae and one pair of lyrifissures. In T. helenae and T. jarretti , the sternal shield is more extensive, with one or two pairs of setae and two pairs of lyrifissures, and extending posteriorly to at least the mid-level of coxae II.

The only other species of Thinoseius in which the female has been adequately described as having a normal anal shield and the first pair of sternal setae inserted on sclerotised plates are T. acuminatus Evans 1962 (Britain) , T. occidentalipacificus Klimov 1998 ( Russia) and T. brevisternalis ( USA). All of these are distinguished from T. variabilis by the fusion of the sternal shield fragment with the endopodal plates between coxae I and II (unfused in T. variabilis ).

Figures

FIGURES 104–109. Thinoseius variabilis, female. 104, dorsal shield; 105, ventral idiosoma; 106, sternal shield, five different specimens; 107, hypostome; 108, epistome, four different specimens; 109, chelicera. Scale bar = 100 µm for 104, 105; 50 µm for 106, 107, 108, 109.