Macrocheles pratum, Knee, Wayne, 2017

Knee, Wayne, 2017, New MacrochelePratums species (Acari, Mesostigmata, Macrochelidae) associated with burying beetles (Silphidae, Nicrophorus) in North America, ZooKeys 721, pp. 1-32 : 6-11

Macrocheles pratum sp. n. Figs 5, 6, 7, 8, 13B

Material examined.

Type material. Holotype: female (CNC829441) on Nicrophorus marginatus (N336, female) collected in Kearney Co., Nebraska, USA, vi.2009, coll: W. Knee & W. Hoback.

Paratypes (11): eight females (CNC829442-829449) with the same collection information as the holotype; two females (CNC829450, 829451) on N. hybridus (N242, female), Onefour, Alberta, Canada, 18.vii.2002, coll: W. Knee & D. Johnson; female (CNC829452) on N. guttula (N235, female), Onefour, Alberta, 17.vi.2003, coll: W. Knee & D. Johnson.

Other material. 184 mites examined from Alberta and Nebraska on Nicrophorus guttula , N. hybridus , N. marginatus , N. obscurus , and N. pustulatus (Table 1).

Diagnosis female.

All dorsal and ventral setae smooth and spinose, except J5 barbed and much shorter than Z5. Seta j1 simple with rounded tip, j1 slightly longer than z1. Dorsal hexagonal setae slightly longer than marginal and submarginal setae. Dorsal shield with moderate reticulations throughout, except smooth in dorsal hexagonal area and between j4 setae, without well-defined procurved line, sigillary rami absent. Sternal shield more than twice as wide as long, punctures moderate size, posterior margin concave. Well defined l.m.t. and l.o.a.; l.o.a. contacts l.m.t. Well defined l.arc. contacts l.o.a., l.ang. and l.o.p. well defined laterally but faint medially. Well defined a.p.l., but a.p.p. not well defined. Ventrianal shield longer than wide (ratio 1.4). Arthrodial brush as long as movable digit. Genu IV with six setae. Femur IV setae ad2, pd1 prominent spikes with flattened forked tip.

Description female.

Dorsal idiosoma (Fig. 5). Dorsal shield 520 (469-547) long and 358 (323-379) (n=8) wide (level with r3), with 28 pairs of setae, all setae simple and spinose except J5 barbed. Seta J5 9 (8-10) half as long as Z5 22 (18-23). Seta j1 simple with rounded tip, j1 20 (19-21) longer than z1 16 (13-18). Marginal and submarginal setae simple, shorter (19) than dorsal hexagonal setae 25 (24-28). Dorsal shield with moderate reticulations throughout, except smooth in dorsal hexagonal area and between j4 setae, shield without well-defined procurved line, sigillary rami absent, and posterolateral margins narrowed slightly. Shield with 22 pairs of pore-like structures, of which six are secretory glands and 16 are non-secretory poroids.

Ventral idiosoma (Figs 6, 13B). Sternal shield more than twice as wide as long, medial length 92 (86-99), maximum width 217 (196-224) level with a.p.l., and minimum width 114 (110-119) posterior of st1. Sternal shield punctures moderate size, posterior margin concave. Setae st1-3 40 (35-45) simple and spinose, and two pairs of lyrifissures (iv1, iv2) on sternal shield. Pear-shaped metasternal shields well separated from sternal shield margin bearing lyrifissure iv3 anteriorly and spinose seta st4 35 (33-39) posteriorly. Well defined l.m.t. and l.o.a., l.o.a. contacts l.m.t. Well defined l.arc. contacts l.o.a., l.ang. and l.o.p. well defined laterally but faint medially. Well defined a.p.l., a.p.p. not well defined. Genital shield length 151 (138-158), width 112 (99-122) level with st5. Genital shield truncate posteriorly and hyaline margin rounded anteriorly, spinose seta st5 32 (30-34) on shield, pair of lyrifissures iv5 off shield near posterior margin. Transverse line on genital shield well defined laterally and faint medially, small punctures along transverse line. Peritrematal shield narrow, fused to dorsal shield near r3, peritreme extends beyond posterior margin of coxa I, two poroids (id3, id7) and one gland (gd3) on the shield. Ventrianal shield longer than wide (ratio 1.4); length 186 (168-194), width 135 (122-146) level with JV2. Ventrianal shield bearing several faint transverse lines, three pairs of simple spinose preanal setae JV1-JV3 26 (21-29), spinose pan 25 (22-28) and pon 18 (15-19), narrow cribrum and a pair of glands (gv3) on shield margin posterior of the anal opening. Ventral opisthosomal setae in soft integument simple and spinose, ZV1 17 (13-23), ZV2 25 (21-27) as long or nearly as long as Jv setae. Two pairs of glands (gv2 and unknown paired-pore) and four pairs of poroids (ivo, ivp) in opisthosomal soft integument.

Gnathosoma (Fig. 7). Basis capitulum medial length excluding internal malae 115 (113-116), width 139 (134-143) posterior to pc. Subcapitular setae simple: h1 44 (41-48), h2 16 (13-18), h3 57 (51-62), and pc 20 (19-23). Palp chaetotaxy normal for genus (2 –5–6–14– 15), palp apotele three-tined, al setae on trochanter, femur and genu slightly spatulate. Corniculi pointed, maximum length 39 (35-45), internal malae slender and smooth. Epistome tripartite with bifid central element bearing small fringe medially, lateral elements broad and flag-like distally, epistomatic margin finely serrate. Subcapitulum with seven rows: six rows have deutosternal denticles, the anterior most, and two posterior most rows with few (four) denticles laterally; the second anterior most row with paired ridges without any denticles. Chelicerae robust, length of second cheliceral segment including fixed digit 135 (122-141), and movable digit 49 (45-52). Fixed digit bidentate with one large and one small tooth, movable digit with a bidentate tooth flanked by a small tooth distally. Pilus dentilis and dorsal seta on fixed digit simple spikes, fixed digit with lyrifissure on each paraxial and antiaxial faces. Movable digit with narrow fringed arthrodial corona, and plumose arthrodial brush (47) almost as long as movable digit.

Legs (Fig. 8). Excluding ambulacra, lengths of leg I 418 (409-432), leg II 390 (362-438), leg III 340 (319-358), and leg IV 474 (463-490). As in all Macrocheles ambulacra only present on legs II–IV, claws II–IV well developed. Pair of glands (gc) on coxa I. Setation of legs I–IV normal for Macrochelidae : coxae 2 –2–2– 1; trochanters 5 –5–5– 5; femora I (2 –3/1,2/3– 2), II (2 –3/1,2/2– 1), III (1 –2/0,1/1– 1), IV (1 –2/1,1/0– 1); genua I, II (2 –3/1,2/1– 2), III (1 –2/1,2/0– 1), IV (1 –2/1,2/0– 0); tibiae I (2 –3/2,2/1– 2), II (2 –2/1,2/1– 2), III, IV (1 –1/1,2/1– 1); tarsus I 20 setae plus numerous tapered setae dorsoterminally, tarsi II–IV 18. Most leg setae simple, setiform, femur II ad1, III pd1, IV ad2, pd1, and genu II ad3 prominent spike setae with flattened forked tip with two to four tines that can appear as a single tapered point viewed laterally. Tarsus II with four large distal, and one ventral, spike setae with thickened conical base and rounded tip. Tarsi III, IV with four distal spike setae with wide base and flexible filamentous tip. Genu and tibia IV with slight ridge posterolateral.

Male and immatures.

Unknown.

Etymology.

Pratum (Latin neuter noun) means “meadow”. This species was only collected in Kearney County, Nebraska and Onefour, Alberta, which are in the prairies.

Remarks.

The female of Macrocheles pratum sp. n. is most similar to those of M. willowae sp. n., M. nemerdarius , M. spinipes Berlese, and M. grossipes Berlese. Macrocheles pratum sp. n. differs from M. willowae sp. n. as outlined in the M. willowae sp. n. description.

Female M. pratum sp. n. differs from that of M. nemerdarius in having larger more prominent punctures on the sternal shield, the posterior margin of the sternal shield is more concave, pon seta is smooth not weakly pilose, j1 is only slightly longer than z1 not 1.5 times as long, J5 is shorter and broader for M. pratum sp. n. (9) than for M. nemerdarius (13), and the ventrianal shield is narrower, length to width ratio of 1.4 for M. pratum sp. n. and 1.2 for M. nemerdarius . Measurements were made examining M. nemerdarius holotype specimen loaned from the National Museum of Natural History, Smithsonian Institution.

Macrocheles spinipes and M. grossipes are associated with coprophilous beetles ( Krantz 1988). Female M. pratum sp. n. differs from those of M. spinipes and M. grossipes in having larger more prominent punctures and transverse lines on the sternal shield, the posterior margin of the sternal shield more concave, arthrodial brush nearly as long as movable digit and not half or three quarters as long as movable digit, setae ad2 and pd1 on femur IV are large spike-like setae with flattened forked tips with two to four tines, ventrianal shield tapers relatively more towards posterior starting anterior of pan setae, and ventrianal shield is narrower, length to width ratio of 1.4 for M. pratum sp. n. and 1.2 for M. spinipes and M. grossipes . Measurements were made examining M. spinipes and M. grossipes voucher material from the Oregon State University Arthropod Collection.