Orthadenella coulsoni, Gwiazdowicz & Marchenko & Teodorowicz, 2014

Gwiazdowicz, Dariusz J., Marchenko, Irina I. & Teodorowicz, Ewa, 2014, Description of Orthadenella coulsoni sp. nov. (Acari: Mesostigmata: Melicharidae) from Siberia with a key to the females of Orthadenella, Journal of Natural History 49 (27), pp. 1659-1671 : 1661-1670

publication ID	https://doi.org/ 10.1080/00222933.2014.974706
DOI	https://doi.org/10.5281/zenodo.4324243
persistent identifier	https://treatment.plazi.org/id/03EA8788-FFD9-FFE7-576C-FEC1FC30FA6A
treatment provided by	Carolina
scientific name	Orthadenella coulsoni
status	sp. nov.

Treatment

Orthadenella coulsoni sp. nov.

( Figures 1 View Figure 1 , 2 View Figure 2 , 3A–G View Figure 3 , 4A–D View Figure 4 , 5 View Figure 5 , 6A–D View Figure 6 )

Type material

Holotype. Female, North Altai (51° 30 ′ N, 85° 02 ′ E), 700 m asl, Shebalino District , Larix sibirica forest, on the hillside, in litter, 17 August 2011, coll. I.I. Marchenko. GoogleMaps

Paratypes. Two females, the same data as holotype; 11 females, North Altai (51° 08 ′ N, 85° 34 ′ E), 1200 m asl., Shebalino District , environs of Topuchaja village , swamped forest of Picea sibirica , in litter, 10 June 1999, coll. I.I. Marchenko GoogleMaps ; five females and eight males, Central Altai (50° 12 ′ N, 88° 03 ′ E), Kurai Ridge foothills, 2000 m asl., floodplain river Kuraika , shrub, in litter, 16 July 1964, coll. S.K. Stebaeva. GoogleMaps

Diagnosis

Female (n = 19). Idiosoma oval, 400–420 µm in length and 225–240 µm in width.

Dorsal. Holodorsal shield bearing 43 pairs of simple setae and among them 20 are situated on the opisthonotal posterior part. The shortest setae are given (in µm): j2 (7–8), j3 (10–11), z1 (5–7), z2 (10–12), s1 (6–7), J5 (7–10); the longest are those labelled j1 (20–22), Z5 (38–41), Z4 (25–26), S4 (25–27) and S5 (25–27). Other seta in j, z and s rows, on the podonotal part, are of a median length from 12 to 17 µm and are as follows: j4 (13–15), j5 (15–17), j6 (15–17), z3 (12–15), z4 (12–15), z5 (12–15), z6 (12–15), s2 (10–12), s3 (12–15), s4 (12–15), s5 (12–15), s6 (12–15), and slightly longer in J, Z and S rows, on the opisthonotal part, from 15 to 22 µm, consecutively: J1 (15–17), J2 (15–17), J3 (15–17), J4 (20–22), Z1 (15–17), Z2 (15–17), Z3 (15–17), S1 (17–22), S2 (17–22), S3 (17–22). All setae in the marginal row r–R are located on the shield, none on the soft membrane. They range in length in a row r from 15 to 17 µm, r2 (15–17), r4 (15–17), r5 (15–17), r6 (15–17), excepting humeral setae r3 = 21 µm, and in row R are about 17 to 20 µm as given: R1 (17–20), R2 (17–20), R3 (17–20), R4 (17–20), R (17–20). Setae r2–R5 at clearly delineated marginal strip. Holodorsal shield is more or less conspicuously covered with a reticulate ornamentation ( Figure 1 View Figure 1 ).

Ventral. The tritosternum with base 10–11 µm wide and 14–15 µm long with laciniae 57–62 µm long (excluding base) with a fused area, free area for about 0.7 of total length ( Figure 3A View Figure 3 ). Anteriorly to the sternal shield lie two pairs of small presternal platelets. Outer platelets are smaller (5–7 × 3 µm) than the inner ones (11–15 × 5 µm). Sternal shield reaches 90–92 μm in length at the midline, and 120–130 μm in width at the widest point, that is, at a level between the first and the second coxae. It bears three pairs of simple setae totally, of lengths: st1 (23–25 µm), st2 = st3 (17–20 µm). As well as pair of gland pores gst1 at the extensions between coxae I–II and two pairs of lyrifissures iv1, iv2, but the third pair of sternal lyrifissures iv3 is absent either on the sternal shield nor metasternal shields. Posteriorly to the sternal shield are small rounded metasternal shields (10 × 10 µm), with a setae st4 (19–20 µm) on it. Inner to coxae II–IV are archwise endopodal shields embracing the coxae, underlying an epigynal shield and partially fused to it. Epigynal shield broad (82–88 µm), and almost of the same length (c. 90 µm at the midline), truncate, with a pair of setae st5 (15–20 µm). Paragenital poroids iv5 are located outside the epigynal shield. Four scanty sclerites arranged in a one line are located posterior to an epigynal shield. Heart-shaped ventrianal shield 145–150 µm length and 155–165 µm width with 15 setae. The shortest are the para-anal setae (13–15 µm), noticeably longer is the postanal seta (24–25 µm) and ventral setae ranging from 18 µm to 21 µm as given (in µm): JV1 (18–21), JV2 (18–21), JV3 (18–21), JV4 (18–21), ZV2 (18–21) except shorter ZV3 (15–17). Likewise, the sternal, genital and ventrianal shields are covered with a reticulate ornamentation ( Figure 2 View Figure 2 ). Outside the ventrianal shield remain four pairs of simple setae (including UR3 = 17–20 µm) JV5 (28–30), ZV4 (16–20), ZV5 (20–21). Peritremes long, reaching above the coxae I, stigmatas at the level of coxae IV. Peritrematal shields narrow, connected with an exopodal strip alongside coxae IV. Peritrematal–exopodal shields fused, with poroids ip1, ip2, ip3 and pores gp2, gp3, gv 2. Posterolaterally to the coxae IV on each side arise two pairs of metapodal sclerites. Those proximal to the coxae IV are smaller (4–6 × 4–6 µm), than further ones (20–21 × 11–13 µm). Sperm access system is that of a Laelapid type, with a sacculus comprised of a thick and porous layer with a numerous thin filaments ( Figure 3C View Figure 3 ).

Gnathosoma . Corniculi are elongated, 26–30 μm long and 10 µm wide; seven rows of denticles are located in the hypostomatal groove (2–6 denticles per row); hypostomatal setae are simple of variable length: h1 –20–21 μm, h2 –21–22 μm, h3 –14–16 μm, h4 – 22–24 μm ( Figure 3B View Figure 3 ). Internal malae as long as corniculi, with a fringed laterobasal margins. Epistome with anterior margin irregularly convex, finely denticulate ( Figure 3D View Figure 3 ). Cheliceral fixed digit 38–40 µm long with a stout pilus dentilis; masticatory surface with a row of 12 teeth and two subapical teeth in addition to apical tooth. Cheliceral movable digit (37–39) tridentate in addition to apical hook; with a transverse-diagonal groove, which appears on the basal one-third of ventral side of chelicera. Dorsal cheliceral seta, dorsal and lateral (antiaxial) lyrifissure distinct ( Figure 3E View Figure 3 ). Palps 126–128 μm long ( Figure 3F, G View Figure 3 ).

Legs. Variable in length: I – 320–340 μm, II – 250–260 μm, III – 240–250 μm, IV – 315–325 μm. Chaetotaxy of legs is peculiar for genus Orthadenella : leg I: coxa, trochanter, femur, genu, tibia (2, 6, 12, 13, 13), leg II (2, 5, 11, 11, 10), leg III (2, 5, 7, 9, 8), leg IV (1, 4, 6, 9, 9) ( Figure 4A, B, C, D View Figure 4 ).

Male (n = 8) Idiosoma oval, 330–355 µm in length and 212–222 µm in width.

Dorsal. Holodorsal shield bearing 43 pairs of simple setae, including 23 podonotal pairs (j1-j6, z1-z6, s1-s6, r2-r6) and 20 opisthonotal pairs (J1-J5, Z1-Z5, S1-S5, R1- R5). Dorsal shield lightly reticulate. Measurements of podonotal setae precisely (in µm): j1 (12–15), j2 (15–17), j3 (12–15), j4 (12–15), j5 (12–15), j6 (12–15), z1 (8–10), z2 (15–17), z3 (12–15), z4 (12–15), z5 (12–15), z6 (12–15), s1 (12–15), s2 (15–17), s3 (12– 15), s4 (15–17), s5 (12–15), s6 (12–15), r2-r6 (12–15). Measurements of opisthonotal setae as follows (in µm): J1 (10–12), J2 (10–12), J3 (12–15), J4 (15–17), J5 (5–6), Z1 (12–15), Z2 (12–15), Z3 (12–15), Z4 (17–20), Z5 (28–30), S1 (12–15), S2 (12–15), S3 (12–15), S4 (15–17), S5 (17–20), R1-R5 (12–15). Setae r2–R5 at clearly delineated marginal strip, likewise for female.

Ventral. Tritosternum with base 7–10 µm wide and 12–15 µm long with laciniae 42– 47 µm long (excluding base) with a fused area, free area for about 0.7 of total length ( Figure 6A View Figure 6 ). Presternal area with a pair platelets. Peritrematal shields and peritremes as in female (poroids ip1, ip2, ip3 and pores gp2, gp3, gv 2 are present). Sternitigenital shield 137–145 µm long and 100–113 µm wide at level between coxae II–III; finely ornamented anteriorly between setae st1 and st3, posteriorly between st4 and st5, and lineate along lateral margins. Sternal shield with a pair of gland pores gst1 at extensions between coxae I–II and with two pairs of lyrifissures iv1, iv2. Shields with five pairs of setae. Measurements of sternal setae as given (in µm): st1 (20–21), st2 (18–20), st3 (16–18), st4 (15–16), st5 (14–15). Ventrianal shield ornamented, midlength (130–145 µm), greatest at midlateral width (155–170 µm) at the level of seta JV1, with a regularly convex lateral margins, bearing five opisthogastric setae JV1 (14–15), JV2 (15–17), JV3 (14–15), JV4 (14–15 µm), ZV2 (14–15), pair of circumanal setae (14–15) and post-anal seta 20 µm; bearing two pairs of poroids and pair of pores gv3; soft opisthogastric cuticle stays with three pairs of setae JV5 (20), ZV4 (13–14), ZV5 (14–15). Opisthogastric setae ZV3 and UR3 are absent contrary to female ( Figure 5 View Figure 5 ).

Gnathosoma . Deutosternum with seven rows of denticles; margins of deutosternal groove delineated laterally except posteriormost row. Number of denticles in each row varies individually in specimens: the first posteriormost row (5–9 denticles), the second row (8–12), the third row (5–6), the fourth row (4–5), 5–7 rows (2–4 in each row). Subcapitulum with a hypostomatic setae h1 (20–22), h2 (15–17), h3 (20–22), h4 (20–22); with three pockmarked delineated areas between h2-h3 and palpcoxal seta h4. Form of corniculi as in female, 22 µm long and 7–8 µm width; internal malae longer than corniculi, with fringed lateral margins basally ( Figure 6B View Figure 6 ). Cheliceral fixed digit 30–32 µm long with a stout pilus dentilis and usually with six teeth in addition to apical tooth: two large basal teeth and two smaller medium-sized teeth at a masticatory surface and two subapical teeth. Cheliceral fixed digit of one sample (eighth examined sample) with nine teeth: three large basal teeth, four medium-sized teeth at masticatory surface and two subapical teeth in addition to apical tooth. Movable digit (28–30 µm) with one tooth in addition to an apical tooth. Spermatodactyl 43–45 µm long with a hyaline ridge above internal canal along its entire length ( Figure 6C View Figure 6 ). Dorsal cheliceral seta, dorsal and lateral (antiaxial) lyrifissure distinct. Epistome with an anterior margin irregularly convex, finely denticulate ( Figure 6D View Figure 6 ).

Legs. Variable in length: I – 260–290 µm, II – 215–225 µm, III – 200–210 µm, IV – 260–290 µm. Leg structure and setation as in female.

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.

Differential diagnosis

The morphometric analysis of O. coulsoni shows many different diagnostic characters from the other two species of Orthadenella . Even a simple analysis of setae measurements gives both similarities (the same lengths of setae Z4, Z5, and setae J1, J2, J3, J4, Z1, Z2 longer by 6–7 μm, and vertical j1 shorter by 4 μm) and dissimilarities when compared to O. tennesseensis . A shared character between O. coulsoni and O. lawrencei is a marked dorsal reticulated patterning covering almost the whole shield, while in O. tennesseensis , this is reticulated only on the posterior and anterior border. Moreover, O. coulsoni and O. lawrencei have a humeral seta r3 conspicuously longer than the remaining setae in the marginal row r–R, which O. tennesseensis does not. This character is repeated in the S4, S5 and Z5 pairs of setae. However, O. lawrencei setae Z4 are identical to the Z1–Z3 setae, whereas in O. coulsoni these setae are dissimilar. In addition, the location of pore iv5 is a further diagnostic character. This pore lies outside the genital shield of both O. coulsoni and O. tenessensis but, as is more common, on the shield in O. lawrencei . A very fine character separating the species is the appearance of a ventrianal shield. This has a characteristic concave anterior boarder at the level between the genital and metapodal sclerites for the entire genus, but differs in shape among species. That of O. coulsoni is wider than long, contrary to the other species. Likewise, the difference in the number of setae located on the ventrianal shield, excluding a circum-anal setae, is another significant character, differentiating O. tennesseensis , with five pairs, from the two remaining species, each bearing six pairs. The metapodal shields in the opistogastric region clearly distinguish O. lawrencei which possesses only a single pair, while O. coulsoni has two pairs composed of the larger sclerite with a smaller abutting. The epistome of O. tennesseensis and O. lawrencei is a trispinate, median process broadly triangular and extending beyond the apex of the lateral processes, contrary to O. coulsoni , which has convex epistome with homogenous denticles arranged parallel to each other. The spermatheca of O. lawrencei is composed of a sacculus permeated with numerous pores and cylinders, while the spermatheca of O. coulsoni is permeated with numerous pores and thin filaments.

Key to the females of genus Orthadenella

Information concerning O. lawrencei and O. tennesseensis was obtained from published descriptions and illustrations ( Evans 1958; De Leon 1963; McGraw and Farrier 1969; Moraza and Lindquist 2011).

1. Only one metapodal plate on each side of the body behind coxae IV .................. ...................................................................................... O. lawrencei ( Evans 1958)

– Metapodal plates divided into two small plates ................................................. 2

2. Interscutal setae JV4 outside ventrianal shield, length and width of ventrianal shield similar ...................................................... O. tennesseensis ( De Leon 1963)

– Interscutal setae JV4 on ventrianal shield, ventrianal shield wider than long ....... .................................................................................................... O. coulsoni n. sp.

Funding

This study and field work of one of us (I.I. Marchenko) was supported by The Federal Fundamental Scientific Research Programme for 2013–2020 [VI.51.1.7. 30.4].