Halolaelaps coulsoni, Gwiazdowicz & Teodorowicz, 2017

Gwiazdowicz, D. J. & Teodorowicz, E., 2017, Description of Halolaelaps coulsoni n. sp. (Acari, Halolaelapidae) from the High Arctic, Acarologia 57 (2), pp. 393-406 : 395-405

Halolaelaps coulsoni n. sp.

Zoobank: A137B515-F6D2-4DCF-8AB7-1B325D60923B

Specimens examined — Holotype. Female. Spitsbergen, Pyramiden (78°40’N, 016°27’E), kittiwake nest detritus, July 16 2012, coll. S.J. Coulson and D.J. Gwiazdowicz; Paratypes: in the same location and date as holotype, two deutonymphs, coll. S.J. Coulson and D.J. Gwiazdowicz ; three females, one deutonymph, four males in the same location, September 13 2012, coll. S.J. Coulson and A. Sjöblom.

Female (n=4), idiosoma oval, 690 – 730 µm in length and 430 – 450 µm in width.

Dorsal idiosoma — On dorsal side two shields of irregular edges - podonotal length 280 – 310 and width 340 – 380 µm and opisthonotal (280 – 310 × 300 – 340 µm) ( Fig. 1A ). Podonotal shield bearing 22 – 23 pairs of simple setae (6 per row "j", "z" and "s", and 4 or 5 setae in row "r"). Accordingly opisthonotal shield - usually with 14 pairs of simple setae. The total number of setae on both shields varies and this fact has been underlined in the section "Morphological variation". Lengths of setae on podonotal shield also vary, for example, that of "j" row are median in length (25 – 28 µm), while posterior setae in rows "z" and "s" (z5, z6, s5, s6) are noticeably longer (47 – 50 µm). The shortest are z1 (7 – 11 µm). Fine areolate ornamentation covers the shield in the area between "j" and "z" rows. Opisthonotal shield with a characteristic irregular incision in the middle (45 – 55 µm), starting from the anterior edge and running between setae J1-J1 and J2-J2. Similar to setae on podonotum, setae on opisthonotum differ in length e.g. J1-J3 are shorter (34 – 38 µm), slightly longer are J5, Z1, Z2 (41 – 45 µm), and the longest are Z4, S4 (57 – 58 µm). The anterior part of the shield between setae J1, Z1, S1 and J2, Z2, S2 is covered with delicate areolate ornamentation.

Ventral idiosoma — Tritosternum with elongate trapezoidal base (25 – 28 µm) and fine lightly pilose laciniae (42 – 47 µm) ( Fig. 2A ). A pair of lightly sclerotized pre-sternal plates fused with sternal shield. Sternal shield rectangular (105 – 115 × 80 – 90 µm) with three pairs of simple setae st1-st3 (21 – 25 µm) and two pairs of pores ( Fig. 1B ). Pair of setae st4 (29 – 32 µm) on soft integument. Epigynial shield peculiar (105 – 115 × 70 – 75 µm); epigynial setae on the edges of a shield, simple (30 – 32 µm); beneath epigynial (genital) shield, between setae JV1 a ZV1 lies a pair of narrow platelets (18 – 21µm). Three pairs of free narrow in shape endopodal plates present between coxae I/II, II/III and the largest between III/IV. Peritreme 260 – 280 µm long mounted on a broad peritrematal shield. Stigma on the horizontal line of coxae IV. Posteriorly to peritrematal shield lie two pairs of oval metapodal plates, a bigger outer platelets (21 – 25 × 10 – 12) µm and smaller inner platelets of 13 – 15 × 5 – 6 µm. Anal shield oval in shape (125 – 135 × 112 – 115 µm) with three typical circum-anal setae (45 – 48 µm). Between genital and anal shield are 8 – 9 pairs of simple setae (33 – 40 µm).

Gnathosoma — Corniculi short and robust, internal malae short, smooth. Palp coxal setae short (21 – 23 µm), internal posterior setae h3 longer (30 – 32 µm), external posterior setae h2 shorter (13 – 15 µm) and rostral setae h1 longer (28 – 31 µm). Hypostome with 8 transverse rows of denticles (8 – 15 denticles per row), denticles in each row irregular in size, and spacing ( Fig. 2D ). Tectum rounded with multiple small denticles ( Fig. 2C ). Chelicera with first and second segments slender, elongate (38 – 40 µm); fixed digit with two triangular distal teeth, pilus dentilis short, spine-like, dorsal cheliceral seta thick, prostrate. Movable digit slender (37 – 41 µm), with three distal triangular teeth ( Fig. 2B ). Palps 80 – 85 µm long ( Fig. 2E, F, G ), palp apotele three-tined.

Legs — Variable in length, pretarsi equipped with claws and rounded pulvilli: I - 420 – 440 µm, II - 340 – 360 µm, III - 350 – 370 µm, IV - 430 – 450 µm. Chaetotaxy of legs is peculiar for genus Halolaelaps : leg I (coxa 2, trochanter 6, femur 13, genu 12, tibia 11), leg II (2, 5, 11, 10, 10), leg III (2, 5, 6, 9, 8), leg IV (1, 5, 6, 9, 8) ( Fig. 3A, B, C, D ).

Male (n=4), idiosoma oval, 470 – 520 µm in length and 310 – 340 µm in width.

Dorsal idiosoma — On a dorsal side two shields are present: podonotal (285 – 290 × 320 – 330 µm) with 23 pairs of simple setae and opisthonotal (200 – 210 × 290 – 300 µm) with 19 pairs of simple setae. Podonotal setae of varied lengths e.g. j1, j2, j6, z5 (28 – 32 µm), j3, j4, (37 – 38 µm) and s4, s5, s6 (44 – 46). Similar to the former, opisthonotal shield bears setae of different lengths e.g. J1, J2 (25 – 31 µm), J3 (21 – 24 µm), J4, J5 (17 – 21 µm), Z1, Z2, Z3, Z4, Z5 (36 – 42 µm), S1, S2, S3, S4 (45 – 51 µm). However, there is no anterior median incision in the opisthonotal shield which is present in the female. Both shields covered with delicate areolate ornamentation ( Fig. 4A ).

Ventral idiosoma — Tritosternum with elongate trapezoidal base (18 – 20 µm) and fine lightly pilose laciniae (31 – 34 µm) ( Fig. 5A ). Sternogenital shield long and narrow (220 × 120 – 125 µm) with five pairs of simple setae (23 – 26 µm) ( Fig. 4B ). Presternal and endopodal plates fused with sternogenital shield. Genital opening at a height of coxae I/II. Peritreme 115 – 125 µm long and mounted on a broad peritrematal shield, stigma at a height of coxae IV. Pair of metapodal plates present, that of greater size (20 – 23 × 10 – 12 µm) and less size (12 – 14 × 6 – 8). Ventrianal shield with irregular edges bearing 5 – 6 pairs of simple setae (26 – 37 µm) and three even circum-anal setae (30 – 32 µm).

Gnathosoma — Corniculi short and robust, internal malae short and smooth. Palp coxal setae short (17 – 19 µm), internal posterior setae h3 longer (25 – 27 µm), external posterior setae h2 shorter (12 – 14 µm) and rostral setae h1 longer (26 – 28 µm). Hypostome with 8 transverse rows of denticles (6 – 9 denticles per row) all equal in size and spacing ( Fig. 5D ). Tectum rounded with multiple small denticles ( Fig. 5C ). Fixed digit of chelicera with two triangular distal teeth, pilus dentilis short, spinelike. Movable digit slender, with one distal triangular tooth and spermatodactyl (38 – 39 µm) ( Fig. 5B ). Palps similar to female’s, slightly smaller (70 – 75 µm) ( Fig. 5E, F, G ).

Legs — Variable in length: I - 430 – 450 µm, II - 320 – 340 µm, III - 340 – 360 µm, IV - 440 – 450 µm. Chaetotaxy of male is similar to female: leg I (coxa 2, trochanter 6, femur 13, genu 12, tibia 11), leg II (2, 5, 11, 10, 10), leg III (2, 5, 6, 9, 8), leg IV (1, 5, 6, 9, 8) ( Fig.6 A, B, C, D ). The marked difference is the presence on femur II and genu III of two spiniform setae as well as that on coxae II and III there are not simple but singular spiniform setae.

Deutonymph (n=3), idiosoma oval, 480 – 520 µm in length and 320 – 340 µm in width.

Dorsal idiosoma — Dorsal side bearing two shields: podonotal (260 × 280 µm) with 23 pairs of simple setae and opisthonotal (220 × 260 µm) with 14 pairs of simple setae ( Fig. 7A ). Podonotal setae of varied lengths e.g. the shortest are z1 (9 µm), slightly longer j1 (20 – 22 µm), r2, r3 (25 – 27 µm), the remaining setae long (30 – 35 µm). The same variation can be seen on the opisthonotal shield where the shortest are J3, J4, J5 (14 – 17 µm), slightly longer than J1, J2 (21 – 24 µm), the remaining setae the longest (25 – 30 µm). As in the male, the opisthonotal shield lacks an anterior median incision. Both shields covered with delicate areolate ornamentation.

Ventral idiosoma — Tritosternum with elongate trapezoidal base (25 µm) and fine lightly pilose laciniae (45 µm) ( Fig. 8C ). Sternal shield long and narrow (220 × 120 – 125 µm) with five pairs of simple setae (26 – 31 µm). Pre-sternal plates combined with sternal shield. ( Fig. 7B ). Three pairs of narrow free endopodal plates present between coxae I/II, II/III, III/IV. Peritreme 225 – 230 µm long located on a wide peritrematal shield at height of coxae II/IV. Posterior of coxae IV lie oval metapodal plates (21 × 12 µm). Anal shield (88 – 91 µm × 95 µm) with three circumanal setae: two para-anals (20 – 21 µm) and one postanal (30 – 32 µm). Between the sternal and anal shields nine pairs of simple setae (21 – 26 µm) occur.

Gnathosoma — Corniculi short and robust, internal malae short, smooth. Hypostomatal setae of differentiated lengths: rostral setae h1 (23 – 24 µm), external posterior setae h2 (11 – 12 µm), internal posterior setae h3 (27 – 29 µm), palp coxal setae (20 – µm). Hypostome with 8 transverse rows of denticles (from 5 – 6 to 9 – 10 denticles per row) ( Fig. 8D ).

Tectum rounded with multiple small denticles ( Fig. 8B ). Chelicera the same as female (29 – 30 µm); fixed digit with two triangular distal teeth, pilus dentilis short. Movable digit slender, with three distal triangular teeth ( Fig. 8A ).

Legs — Variable in length: I - 380 – 400 µm, II - 310 – 330 µm, III - 310 – 220 µm, IV - 370 – 390 µm. Leg chaetotaxy in deutonymph is similar to female: leg I (coxa 2, trochanter 6, femur 13, genu 12, tibia 11), leg II (2, 5, 11, 10, 10), leg III (2, 5, 6, 9, 8), leg IV (1, 5, 6, 9, 8).

Differential diagnosis

Halolaelaps coulsoni n. sp. is similar to Halolaelaps fallax ( Hirschmann and Götz 1968) and Halolaelaps saproincisus (Hirschman and Götz 1968) , due to the characteristic of opisthonotal shield: bears many pairs of setae, has an anterior incision in the middle as well as a similar type of tectum and, moreover, the female has an anal shield instead of ventrianal shield as in some species. However, Halolaelaps coulsoni n. sp. has certain features differentiating it from the species given above. H. saproincisus has some of the podonotal setae, and the majority of opistonotal setae, pilose and thus of a different type from those of both H. coulsoni n. sp. and H. fallax where all setae are simple (aciculate). At this point it should be underlined that setae un- der consideration go in different numbers - H. fallax bears 15 pairs of setae, but Halolaelaps coulsoni n. sp. only 14. Moreover, H. saproincisus on the lateral edges of opistonotal shield has incisions which are not present neither in Halolaelaps coulsoni n. sp. or H. fallax . Another differential character are the proportions of the anal shield: H. fallax has this shield wider than long, H. saproincisus has the shield of the same width and length, while in H. coulsoni n. sp. this shield is considerably longer than wide. H. cousoni n. sp. also has greater endopodal plates than the other Haloalelaps species herein. A final determining characteristics is the tectum: H. fallax and H. saproincisus have this triangular with teeth different in size totally reaching number of 10-15, while H. coulsoni n. sp. has all teeth similar in size and more numerous reaching about 25-30.

Morphological variability

The morphological variability appears to concern mainly differences in the chaetotaxy.

Four females have been analysed and none of them were free of inconsistencies, though different for each female. The most noticeable feature is the lack of setae in "J" row. One female lacks seta J2 on left side of shield and J1 on the right side ( Fig. 1A ); second and third females lack J2 on the right side, and the fourth female lacks both setae J2. First and second females have one setae Z5 laying outside opisthonotal shield but the third has this one on a shield however other seta (S4) present outside of it. On the podonotal shield some setae are absent or otherwise there are additional setae or the occurrence of some setae outside the shield. Morphological changes in chaetotaxy could be observed among leg setation as well. For example, usually on femur I there are 13 setae present but in one female there are 14 setae.

Despite this, morphological changes amongst males and deutonymphs represent not much variation. Some individuals lack of a single seta or have this displaced from the shield to the membrane. In addition, in one deutonymph on genu II instead of the typical 10 setae there are 11 setae.

A similar issue was noticed by Gwiazdowicz et al. (2011) after an analysis of 53 specimens (45 females and 8 males) of Arctoseius haarlovi Lindquist 1963 , where 22 (18 females and 4 males, 41.5%), featured chaetotaxy variability. Although both species have been recorded in High Arctic, it is very unlikely that those changes could be due to a harsh environment conditions, as in other species of mesostigmatid mites from this geographical region such changes have not yet been observed, or at least not in a such numerous and frequent basis.

Etymology

The species is dedicated to our friend, a scientist exploring the invertebrate fauna of the High Arctic, Prof. Dr. Stephen J. Coulson from University Centre in Svalbard, Longyearbyen, Norway.

Acarologia 57(2): 393–406 (2017)

Figures

FIGURE 1: Halolaelaps coulsoni n. sp., female: A – dorsal view of idiosoma, B – ventral view of idiosoma (scale bar 100 µm).

FIGURE 2: Halolaelaps coulsoni n. sp., female: A – tritosternum, B – chelicera, C – tectum, D – gnathosoma, E – palp apotele, F – palp tarsus, G – palp, (scale bar 50 µm).

FIGURE 3: Halolaelaps coulsoni n. sp., female: A – leg I, B – leg II, C – leg III, D – leg IV (scale bar 100 µm).

FIGURE 4: Halolaelaps coulsoni n. sp., male: A – dorsal view of idiosoma, B – ventral view of idiosoma (scale bar 100 µm).

FIGURE 5: Halolaelaps coulsoni n. sp., male: A – tritosternum, B – chelicera, C – tectum, D – gnathosoma, E – palp apotele, F – palp tarsus, G – palp (scale bar 50 µm).

FIGURE 6: Halolaelaps coulsoni n. sp., male: A – leg I, B – leg II, C – leg III, D – leg IV (scale bar 100 µm).

FIGURE 7: Halolaelaps coulsoni n. sp., deutonymph: A – dorsal view of idiosoma, B – ventral view of idiosoma (scale bar 100 µm).

FIGURE 8: Halolaelaps coulsoni n. sp., deutonymph: A – chelicera, B – tectum, C – tritosternum, D – gnathosoma (scale bar 50 µm).