Thinoseius helenae, Halliday, 2010

Halliday, R. B., 2010, Revision of the Australian Eviphididae (Acari: Mesostigmata) 2596, Zootaxa 2596 (1), pp. 1-60 : 35-38

Thinoseius helenae sp. nov.

( Figs 53–69 )

Material examined. Holotype. Female. South Australia. Wright Bay, 25 km south of Kingston SE, 37°02'S 139°44'E, 26 March 2008, R. B. Halliday coll., in deep piles of seaweed on beach (in ANIC) . Paratypes. 141 females, 167 males, same data as holotype ; 1 female, 24 km south of Kingston Beach , 1 April 1982, J. Forrest coll., seaweed on beach ; 26 females, 11 males, Cape Jaffa , 36°56'S 139°40'E, 26 March 2008, R. B. Halliday coll., seaweed on beach (in ANIC) .

Description. Female. Dorsal idiosoma ( Fig. 53 ). Dorsal shield length 444–500 µm, width 271–310 µm (n=5), not completely covering dorsal idiosoma, shield surrounded by striate cuticle postero-laterally and posteriorly, the inner area of this striated cuticle adjacent to shield sometimes dark coloured and partly sclerotised. Shield narrowed anteriorly and rounded posteriorly, with shallow indentations at level of setae Z 1, surface with delicate polygonal ornamentation throughout, with 17 pairs of setae and ca. 10 pairs of minute pores; setae uniform in length (ca. 18–20 µm). Podonotal area of shield with 12 pairs of short thick pointed setae; podonotal setae s 2, s 5, s 6, r 2, r 3, r 5 inserted in striated skin outside shield, all short, thick, pointed. Opisthonotal area of shield with five pairs of short thick pointed setae; setae Z 3, Z 4, Z 5, S 1, S 3, S 4, S 5 inserted in striated skin outside shield.

Ventral idiosoma ( Fig. 54 ). Tritosternum with large trapezoidal base and delicate sparsely pilose laciniae. Anterior margin of sternal shield undulating, expanded to absorb pre-sternal plates and embrace base of tritosternum. Posterior margin irregular and lightly sclerotised, medially eroded to varying degrees ( Figs 60–63 ); shield with two pairs of short pointed setae and two pairs of conspicuous lyrifissures, surface with polygonal ornamentation, often reduced or absent postero-medially. Third pair of sternal setae, third pair of sternal pores, and metasternal setae inserted in soft skin between coxae III. Large triangular endopodal plates present between coxae II–III, narrower endopodal plates present between coxae III–IV, posteriorly abutting narrow plates that embrace coxae IV. Epigynal shield with antero-lateral margins parallel, expanding behind epigynal setae to form a bulbous posterior end; surface of shield with a few faint irregular lineate markings; epigynal setae inserted in soft skin clearly separate from shield. Anal shield wider than long, length ca. 110 µm, width ca. 140 µm, anterior margin strongly convex, postero-lateral margins slightly concave; surface with irregular lineate markings, cribrum very wide and conspicuous, post-anal seta shorter and thicker than para-anal setae. Soft skin between epigynal and anal shields with a long narrow weakly sclerotised strip and three pairs of fine pointed setae; opisthogastric skin lateral to anal shield with three pairs of short thick setae, metapodal plates small, irregular in shape. Peritrematal shields free from dorsal shield, extending from bases of setae j 1 to midlevel of coxae IV, on anti-axial side of peritreme only, posterior margin notched, with one post-stigmatal pore and indistinct lineate markings, exopodal plates absent. Peritremes extending from stigmata at anterior level of coxae IV to anterior of coxae I, at level of seta z 1.

Gnathosoma . Surface of hypostome rugose, with irregular linear markings. Rostral setae h 1 30 µm long, external seta h 2 shorter, 20 µm, inserted postero-lateral to h 3, internal seta h 3 15 µm, palp coxal seta shortest, 10 µm, all fine and needle-like ( Fig. 55 ). Deutosternal groove with irregular margins and five rows of denticles, 4–5 denticles per row, and a smooth anterior line; corniculi robust, slightly curved inward; internal malae fine, lightly fringed. Seta av on palp trochanter longer and thicker than pv, al on palp femur shorter and thicker than pl, al on palp genu short, thick, spine-like, al on tibia shorter and thicker than pl, tarsus without long sensory setae, palp tarsal claw with two subequal spatulate tines. Epistome with five long smooth points, central point longest (20 µm) ( Fig. 56 ). Fixed digit of chelicera with a triangular medial tooth, robust pilus dentilis, and two smaller triangular distal teeth, dorsal seta obscure, apparently minute ( Fig. 57 ); movable digit with a triangular medial tooth and a smaller triangular distal tooth, 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 2/1 2/1 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 ( Fig. 69 ). On femur II, seta ad 3 very fine, displaced anteriorly to an almost antero-lateral position, other dorsal setae on femur II much thicker. Tarsi I– IV each with a well-developed pair of claws and a rounded pulvillus, lateral and median lobes of pulvillus equal in length, claws on tarsus I smaller and less robust than those on tarsi II–IV; paradactyli on tarsi II–IV very long and pointed, projecting well beyond claws ( Fig. 58 ). Coxae I with two pairs of conspicuous coxal glands ( Fig. 54 ).

Genital structures. Sacculus indistinct and apparently unsclerotised, sections of insemination ducts occasionally visible, originating from posterior margin of coxa III ( Fig. 59 ).

Male. Dorsal idiosoma ( Fig. 64 ). Dorsal shield length 381–415 µm, width at level of seta z 5 271–289 µm (n=5), egg-shaped, widest posteriorly, with delicate polygonal ornamentation throughout, with 30 pairs of setae, pores minute, only about three pairs visible. Setae j 2 and z 1 minute; setae in central area of shield thick, smooth and pointed (j 4, j 5, j 6, z 2, z 4, z 5, z 6, s 4, s 5, J 1, J 2, J 3, Z 1, Z 3, Z 4); J 5 short, smooth and pointed; marginal setae long and thick, with lightly sclerotised spatulate tips (j 1, j 3, s 2, r 2, r 3, r 5, s 6, S 1, S 3, S 4, S 5, Z 5).

Ventral idiosoma ( Fig. 65 ). Pre-sternal plates absent. Sternal, epigynal and endopodal shields fused to form a sterno-genital shield, with four pairs of short smooth setae and three pairs of lyrifissures, first pair oriented obliquely, second and third pairs longitudinal. Anterior margin of shield undulating, posterior margin bluntly rounded, surface with indistinct polygonal ornamentation throughout; genital aperture on anterior margin of shield; setae st 5 in soft skin adjacent to posterior end of shield. Anal shield oval, wider than long, with a pair of small lateral protrusions, these variable in shape and size; surface with indistinct lineate markings; post-anal setae more than double length of para-anal setae. Opisthogastric skin between sterno-genital shield and anal shield with three pairs of minute setae and a pair of elongate metapodal plates; skin lateral to anal shield with three pairs of smooth setae, the posterior pair longest and thickest. Peritrematal shield as for female, except posterior end of shield deeply and irregularly notched.

Gnathosoma . Fixed digit of chelicera with a single very large triangular tooth, pilus dentilis and dorsal seta obscure; movable digit edentate except for a low rounded medial ridge; spermatodactyl erect, thick basally, gradually narrowing distally, tip enlarged ( Fig. 66 ). Epistome with five long points, one or more points sometimes distally bifid or trifid ( Fig. 67 ), other features of gnathosoma as for female.

Legs. Most ventral and lateral setae modified into thick heavy spurs with rounded tips, especially on femur and genu of legs I and II ( Fig. 68 ), less pronounced on legs III and IV; legs otherwise as for female.

Etymology. This species is named in honour of my colleague Helen Tongway, who first drew my attention to the mite fauna of seaweed in southeastern South Australia.

Notes. The sternal shield in females of T. helenae is rather variable in form. The anterior margin of the shield always extends forward to cover the pre-sternal area, and has a medial indentation that embraces the base of the tritosternum. The shield always bears two pairs of short pointed setae st 1 and st 2, and two pairs of conspicuous lyrifissures, stp 1 and stp 2. Lyrifissure stp 1 is oriented almost transverse to the body axis, and stp 2 varies from oblique to almost longitudinal in orientation. The surface of the shield has distinct polygonal ornamentation, and the posterior margin of the shield is irregular and medially eroded to varying degrees. In specimens where the shield is most complete, its posterior margin is anterior to stp 2 and posterior to st 2 ( Figs 60, 61 ). In other specimens, the polygonal ornamentation becomes indistinct postero-medially ( Fig. 62 ), or the posterior margin of the shield is deeply invaginated almost to the level of stp 1 ( Fig. 63 ). Despite this variation, the sternal shield of T. helenae is more extensive than that of any other species of Thinoseius . This is the only species in which the sternal shield is extensive enough to incorporate both the second pair of sternal setae and the second pair of sternal lyrifissures.

The paradactyli on tarsi II–IV of this species are very long and pointed, long enough to project well beyond the claws. This structure also occurs in other Eviphididae that occupy very wet habitats ( Mašán & Halliday 2010), and is similar to that of some genera of semiaquatic Blattisociidae ( Lindquist et al. 2009) . However, unlike the Blattisociidae , the median and lateral lobes of the pulvillus in T. helenae are unmodified and rounded, project only slightly beyond the claws ( Fig. 58 ).

Like other species of Thinoseius , T. helenae shows strong sexual dimorphism in secondary sexual characters. The dorsal shield of the male is more extensive than that of the female, and bears the full complement of 30 pairs of setae, compared with only 17 pairs in the female. Many of the dorsal shield setae of the male are strongly modified, either long and robust with spatulate tips, or short, thick, and spine-like ( Fig. 64 ). Many ventral and lateral leg setae in the male are also modified into thick heavy spurs with rounded tips ( Fig. 68 ), while the corresponding setae in the female are fine and pointed ( Fig. 69 ). This trend is strongest in the ventral setae on the femur and genu of legs I and II, but is also developed to a lesser extent on other leg segments. There also appears to be some dimorphism in the shape of the epistome. The epistome of the female has five long anterior points, and there is occasionally a slight bifurcation in the tip of one of these points ( Fig. 56 ). This bifurcation is much more common in the male, and sometimes occurs in several of the points ( Fig. 67 ).

Figures

FIGURES 53–59. Thinoseius helenae, female. 53, dorsal shield; 54, ventral idiosoma; 55, hypostome; 56, epistome; 57, chelicera; 58, pre-tarsus IV, 59, coxa III and insemination duct. Scale bar = 100 µm for 53, 54; 50 µm for 55, 56, 57, 59; 25 µm for 58.

FIGURES 60–63. Thinoseius helenae, female, sternal shield. Four different specimens from Wright Bay, South Australia. Scale bar = 50 µm.

FIGURES 64–69. Thinoseius helenae. 64, male, dorsal shield; 65, male, ventral idiosoma; 66, male, chelicera; 67, male, epistome, three different specimens; 68, male, legs I and II, femur and genu, ventral; 69, female, legs I and II, femur and genu, ventral. Scale bar = 100 µm for 64, 65; 50 µm for 66, 67, 68, 69.