Thinoseius jarretti, Halliday, 2010

Halliday, R. B., 2010, Revision of the Australian Eviphididae (Acari: Mesostigmata) 2596, Zootaxa 2596 (1), pp. 1-60 : 40-45

Thinoseius jarretti sp. nov.

( Figs 70–86 )

Material examined. Holotype. Female. South Australia. Largs Bay (Adelaide), 26 December 2007, D. Jarrett coll., seaweed on beach (in ANIC) . Paratypes. 12 females, 14 males, 168 DN, 12 PN, same data as holotype ; 5 males, 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. (all in ANIC) .

Description. Female. Dorsal idiosoma ( Fig. 70 ). Dorsal shield length 429–505 µm, width 252–289 µm (n=5), not completely covering dorsal idiosoma, shield surrounded by striate cuticle postero-laterally and posteriorly. Surface of shield with polygonal ornamentation throughout, indistinct medially; lateral margins irregular and indistinct; with 18 pairs of setae and ca. seven pairs of minute pores. On podonotal shield, z 1 minute, j 1, j 2, z 2, z 5, z 6 fine and needle-like, j 3, j 4, j 5, j 6, z 4, s 4 longer, thick and spine-like. Podonotal setae s 2, r 2, r 3, r 5, s 5, s 6 moderately thick, inserted in soft lateral skin outside shield. Opisthonotal shield with J 1, Z 1, Z 4 long, thick, spine-like, J 2, J 3, J 5 shorter, fine and needle-like. Opisthonotal setae Z 3, Z 5, S 1, S 3, S 4, S 5 long, thick, spine-like, inserted in soft lateral skin outside shield.

Ventral idiosoma ( Fig. 71 ). Tritosternum with bell-shaped base and finely pilose laciniae. Anterior margin of sternal shield concave, posterior margin indistinct; sclerotised anterior section incorporating setae st 1 and lyrifissures stp 1; weakly sclerotised posterior section tapering to a rounded posterior margin at anterior level of coxae III, weakly sclerotised posterior section bearing lyrifissures stp 2; antero-lateral corners of shield fused with anterior ends of endopodal plates between coxae I–II. Setae st 2 and st 3 inserted in soft skin; metasternal setae st 4 and metasternal pores in soft skin between coxae III. Endopodal plates II–III and III–IV triangular, free. Epigynal shield narrower anteriorly, slightly wider posteriorly, with a few indistinct lines of ornamentation, epigynal setae in soft skin adjacent to shield. Anal shield as long as wide, length and width 100 µm, anus situated in anterior half of shield; shield with triangular lateral projections, these variable in size and shape; para-anal setae and post-anal seta equal in length, post-anal seta thicker; cribrum very large, with lateral arms extending anterior to post-anal seta. Metapodal plates elongate; opisthogastric skin with six pairs of smooth setae, lateralmost pair thickest and longest, and a pair of very narrow transverse post-epigynal platelets. Peritrematal shields narrow, beginning anterior to coxae I and projecting slightly beyond stigmata, with a pair of small post-stigmatal pores; peritremes narrow, extending anterior to coxae I.

Gnathosoma . Rostral setae h 1 30 µm, external setae h 2 shorter, 15 µm, inserted postero-lateral to h 3, internal seta h 3 25 µm, palp coxal seta 15 µm, all fine and needle-like ( Fig. 72 ). Deutosternal groove with slightly irregular margins, with five rows of denticles, 5–6 denticles per row, and a smooth anterior line; corniculi robust, outer margins slightly indented; internal malae fine, lightly fringed. Setae av and pv on palp trochanter subequal in length, av thicker, al and pl on femur similar in length and thickness, al on palp genu shorter and thicker than pl, al on tibia shorter and thicker than pl, tarsus without long sensory setae, palp tarsal claw with two subequal spatulate tines. Epistome variable, with three or four main points, one or more of these points subdivided to varying degrees, sometimes with smaller points between main points ( Fig. 73 ). Fixed digit of chelicera with a small triangular distal tooth and two minute medial teeth, pilus dentilus fine and pointed, dorsal seta obscure, apparently minute ( Fig. 74 ); movable digit with two teeth (the proximal tooth absent on one side of one specimen), 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 and some postero-lateral setae thickened, ventral setae and most lateral setae fine and needle-like. On femur II, seta ad 3 short, displaced anteriorly to an almost antero-lateral position, other dorsal setae on femur II much thicker. Pre-tarsi as for T. helenae . Coxae I with two pairs of conspicuous coxal glands ( Fig. 71 ).

Genital structures. Insemination ducts arising on posterior margin of coxae III, terminating in a sclerotised oval-shaped ramus, sacculus apparently unsclerotised ( Fig. 75 ). Some specimens contain a single large egg, 205 x 230 µm.

Male. Dorsal idiosoma ( Fig. 76 ). Dorsal shield length 373–460 µm, width 252–281 µm (n=5), eggshaped, widest posteriorly, with strong anterior and lateral polygonal ornamentation and scale-like posterior ornamentation, central area smooth, with 30 pairs of setae and about five pairs of minute pores. Seta z 1 minute, fine, j 2, z 5, z 6, J 1, J 2, J 3, J 5 short, fine, j 4, j 5 short, thick, other setae very long and thick, increasing in length and thickness posteriorly, to longest setae Z 4, S 5, 70 µm long.

Ventral idiosoma ( Fig. 77 ). Pre-sternal plates absent. Sternal, epigynal, and endopodal shields I–II and II– III fused to form a sterno-genital shield, endopodal shields between coxae III–IV fused at their anterior ends only. Shield with four pairs of smooth short setae and two pairs of lyrifissures, first pair large, oblique, second pair smaller, oblique; third pair of sternal pores minute, circular. Surface of shield with polygonal ornamentation in anterior half, and a pair of longitudinal sub-marginal lines, anterior margin undulating, posterior margin narrow, rounded, setae st 5 and epigynal pores in soft skin near posterior end of shield. Anal shield wider than long, with a pair of small lateral protrusions, these variable in size and shape, anus in centre of shield, post-anal seta approximately three times length of para-anal setae, cribrum narrow. Opisthogastric skin surrounding anal shield with four pairs of smooth setae, posterior pair longest; metapodal plates large, oval.

Gnathosoma . Hypostome as for female. Setae av and pv on palp trochanter subequal in length, very thick and spine-like ( Fig. 78 ). Epistome variable, with one, two or three long medial points, sometimes with bifid or trifid tips, and a variable number of smaller lateral points ( Fig. 79 ). Fixed digit of chelicera with a single very large triangular tooth, pilus dentilus short and thick, dorsal seta obscure, apparently minute; movable digit with one large triangular tooth, spermatodactyl arising near base of movable digit, slightly longer than movable digit, tip expanded ( Fig. 80 ).

Legs. Chaetotaxy and pre-tarsi as for female. Posteroventral setae on femur I, and femur, genu and tibia II and III longer and thicker than those of female; setae mv and av 2 on tarsi II and III with an inflated bulbous base ( Fig. 81 ).

Deutonymph. Dorsal idiosoma ( Fig. 82 ). Dorsal shield length 358–402 µm, width 229–239 µm (n=5). Shield entire, completely covering idiosoma, without lateral incisions, surface with strong polygonal ornamentation throughout, polygonal shapes elongate antero-laterally and laterally, scale-like posteriorly. Shield with 30 pairs of setae and ca. six pairs of minute pores. Setae j 2 and z 1 minute, z 2, z 5, z 6, J 1, J 2, J 3, J 5 fine and needle-like, other setae long, thick, spine-like, increasing in length posteriorly.

Ventral idiosoma ( Fig. 83 ). Sternal shield with undulating anterior margin, tapering to a bluntly rounded posterior end between coxae IV; surface with polygonal ornamentation throughout except for smooth marginal strip; shield with four pairs of short needle-like setae and two pairs of lyrifissures, first pair transverse, second pair oblique; third pair of sternal pores minute, circular. Endopodal plates I–II fused with sternal shield, endopodal plates II–III and III–IV free. Anal shield trapezoidal, cribrum conspicuous, post-anal seta longer than para-anal setae. Opisthogastric skin between coxae IV with setae st 5 and three narrow indistinct post-genital plates; skin around anal shield with six pairs of short needle-like setae and a pair of elongate metapodal plates. Exopodal plates between coxae I–II and II–III represented by small irregular fragments, exopodal plate IV narrow and elongate.

Gnathosoma . Epistome with five subequal points, one or more points distally bifid in some specimens ( Fig. 84 ). Cheliceral digits shorter and more robust than those of adult female, fixed digit with three moderately large triangular teeth, pilus dentilis short and thick, movable digit with one large triangular tooth and an uneven distal ridge ( Fig. 85 ).

Legs. Chaetotaxy as for adult. Most dorsal and postero-lateral setae thicker than ventral and antero-lateral setae. Pulvillus and paradactyli inconspicuous, not projecting beyond claws.

Protonymph. Dorsal idiosoma ( Fig. 86 ). Length 258–305 µm, width 166–197 µm (n=5). Podonotal shield with smooth surface, except for a series of irregular curved ridges near anterior and antero-lateral margins; with 11 pairs of smooth setae, steae near margins of shield longest; setae r 2, r 3, r 5, s 6 in soft skin outside shield. Opisthonotal shield with 11 pairs of setae; J1 thick and spine-like, Z 3 very hypertrophied, forming a heavy blunt spur, other setae fine and pointed.

Ventral idiosoma ( Fig. 87 ). Inter-coxal region unsclerotised, with three pairs of short pointed setae and two pairs of lyrifissures. Anal shield faintly visible, with a pair of short para-anal setae and a longer post-anal seta; opisthogastric skin with four pairs of setae, posterior pair longest. Peritrematal shield absent, peritremes short and broad, not reaching anterior margin of coxae III.

Etymology. This species is named in honour of Don Jarrett of Adelaide, who collected the specimens.

Notes. The female of T. jarretti has a reduced fragment of sternal shield between coxae I, bearing setae st 1 and lyrifissure stp 1, as is typical for the genus. The lateral corners of this fragment of sternal shield are fused with the anterior ends of endopodal plates I–II. The sternal shield also has a weakly sclerotised but distinct posterior extension, which reaches to the level of coxae III, and carries the second pair of lyrifissures. The outlines of this section of the shield are irregular and variable but it is never completely absent.

Sexual dimorphism in this species takes the form of spectacular differences in the dorsal chaetotaxy. The dorsal shield of the male is more extensive than that of the female, and carries the full complement of 30 pairs of setae, compared with 18 in the female. The setae in the s, r, Z and S series are extremely long and thick, and form a conspicuous fringe of projecting setae around the margins of the shield ( Fig. 76 ). There are also some differences in the opisthogastric region behind coxae IV. The anal shield of the male has a smaller cribrum than that of the female, but a much longer post-anal seta. The opisthogastric skin of the male has four pairs of setae compared with six in the female. There are also differences in the gnathosoma. On the palp trochanter of the female, the two ventral setae are subequal in length, with av thicker than pv ( Fig. 72 ). In the male, these two setae are similar in length to those of the female, but both are very thick, heavy, and spine-like ( Fig. 78 ). The points of the epistome of the male ( Fig. 79 ) are also finer and more numerous than those of the female ( Fig. 73 ). On the palp femur of this species, setae al and pl have migrated slightly onto the ventral surface of the segment, and dorsal seta ad has become almost antero-lateral, so it is partly visible when the specimen is viewed ventrally. Seta ad in the male is much thicker than that of the female. Many ventral setae on the legs of the male are longer and thicker than those of the female, and tarsi II and III in the male have two very distinctive ventral setae with inflated bulbous bases; in the female these setae are unmodified, fine and needle-like.

Some of the dorsal shield setae of this species undergo dramatic transformations during development. In the protonymph, seta Z 3 is greatly expanded to form a very heavy spur, many times thicker than any other opisthonotal seta. In the deutonymph this seta reverts to a more normal form, similar in shape and size to nearby Z and S setae. In the male adult, Z 3 and the other Z and S setae are all greatly expanded in both length and thickness to form a formidable fringe of projecting setae around the margins of the shield. However, in the adult female, seta Z 3 retains the deutonymphal form, similar in shape and size to the other Z setae. In contrast, J 1 is thick and heavy in the protonymph, fine and needle-like in the deutonymph and adult male, and thick and heavy in the female. Some setae including j 3 and j 6 follow a different trajectory; fine and needle-like in the protonymph, long and thick in the deutonymph and both adults.

The dorsal shields of the protonymph, deutonymph and adult male of T. jarretti are developed to a normal degree that is typical for the family Eviphididae , and the deutonymph and adult male carry the normal complement of 30 pairs of setae. The dorsal shield of the female is secondarily reduced in both its extent and the strength of its sclerotisation, and carries only 18 pairs of setae. These dramatic differences between sexes and instars suggest that different life cycle stages are responding to different evolutionary pressures. The long and heavy setae on the dorsal shield of the male, and to a lesser extent the heavier setae on its legs, may be associated with male-male combat during courtship, and the heavily sclerotised dorsal shield and strong dorsal setae of the deutonymph may be associated with phoresy. Opisthonotal setae Z 3 in the protonymph are very hypertrophied to form extremely thick and heavy spurs. The function of these setae is of course unknown, but they bear a striking resemblance to setae S 4 in the protonymph of Neocypholaelaps indica Evans 1963d (Ameroseiidae) . The population of this species consists mainly of deutonymphs - the random sample taken from a single pile of seaweed included 168 deutonymphs, 12 females and 14 males. Further research is required to determine what environmental cue triggers a deutonymph to undergo the final moult to the adult stage.

Figures

FIGURES 70–75. Thinoseius jarretti, female. 70, dorsal shield; 71, ventral idiosoma; 72, hypostome; 73, epistome, four different specimens; 74, chelicera; 75, insemination ducts. Scale bar = 100 µm for 70, 71; 50 µm for 72, 73, 74, 75.

FIGURES 76–81. Thinoseius jarretti, male. 76, dorsal idiosoma; 77, ventral idiosoma; 78, palp trochanter and femur; 79, epistome, four different specimens; 80, chelicera; 81, tarsus II. Scale bar = 100 µm for 76, 77; 50 µm for 78, 79, 80, 81.

FIGURES 82–87. Thinoseius jarretti. 82, deutonymph, dorsal idiosoma; 83, deutonymph, ventral idiosoma; 84, deutonymph, epistome, three different specimens; 85, deutonymph, chelicera; 86, protonymph, dorsal idiosoma; 87, protonymph, ventral idiosoma. Scale bar = 100 µm for 82, 83, 86, 87; 50 µm for 84, 85.