Macrocheles willowae, 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 : 4-6

Macrocheles willowae sp. n. Figs 1, 2, 3, 4, 13A

Material examined.

Type material. Holotype: female (CNC829414) on Nicrophorus orbicollis (N088, female) collected near Dacre, Ontario, Canada (45.369, -76.988), 25.vi.2009, coll: W. Knee.

Paratypes (26): Nine females (CNC829415-829423) with the same collection information as the holotype; 15 females (CNC829424-829438) on N. defodiens (N222, female), Durham, New Hampshire, USA (43.134, -70.926), 07.vi.2009, coll: W. Knee & M. Scott; female (CNC829439) on N. defodiens (N136, female), Prince George, near University of Northern British Columbia campus, British Columbia, Canada (53.904, -122.783), 12.vi.2009, coll: W. Knee & R. Dawson; female (CNC829440) on N. orbicollis (N143, male), Hamilton, Ontario, Canada, 7.vii.2009, coll: W. Knee.

Other material. 1241 mites examined from British Columbia, Nova Scotia, Ontario, Prince Edward Island, Connecticut, Florida, and New Hampshire on N. carolinus , N. defodiens , and N. orbicollis (Table 1).

Diagnosis female.

As for Macrocheles (see Hyatt and Emberson 1988). All dorsal and ventral setae smooth and spinose, except J5 barbed and slightly shorter than Z5. Seta j1 simple with rounded tip, j1 slightly longer than z1. Dorsal hexagonal setae (j5, z5, j6) nearly as long as marginal and submarginal setae (R and UR). 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 small, posterior margin concave. Well defined linea media transversa (l.m.t.) and linea oblique anteriores (l.o.a.), l.o.a. contacts l.m.t. Linea arcuata (l.arc.) well defined and contacts l.o.a. Linea angulata (l.ang.) and linea oblique posteriore (l.o.p.) well defined laterally but faint medially. Area punctata laterale (a.p.l.) well defined, but area punctata posteriore (a.p.p.) not well defined. Ventrianal shield longer than wide (ratio 1.3). 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. 1). Dorsal shield 548 (526-572) long and 357 (344-372) (n=8) wide (level with r3), with 28 pairs of setae, all setae simple and spinose except J5 is barbed. Seta J5 16 (15-18) shorter than Z5 24 (22-27). Seta j1 simple with rounded tip, j1 18 (16-20) slightly longer than z1 16 (12-19). Marginal and submarginal setae simple, slightly longer 24 (23-25) than dorsal hexagonal setae 20 (15-22). 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 2, 13A). Sternal shield more than twice as wide as long, medial length 91 (88-96), maximum width 213 (192-221) level with a.p.l., and minimum width 117 (115-124) posterior of st1. Sternal shield punctures small, posterior margin concave. Setae st1-3 38 (33-43) 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 33 (30-35) 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 149 (141-161), width 113 (104-120) 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 1.3); length 198 (187-204), width 153 (144-168) level with JV2. Ventrianal shield bearing several faint transverse lines, three pairs of simple spinose preanal setae JV1-JV3 26 (21-30), spinose paranal (pan) 27 (25-30) and postanal (pon) 18 (16-20) setae, 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 21 (17-29), ZV2 26 (22-29) 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. 3). Basis capitulum medial length excluding internal malae 114 (106-122), width 150 (143-157) posterior to pc. Subcapitular setae simple: h1 38 (28-48), h2 16 (13-19), h3 53 (44-67), and pc 19 (16-21). 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, length along lateral margin 42 (37-51), 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 of which have deutosternal denticles; the anterior most row with few (four) denticles laterally, and the second anterior most row with paired ridges without any denticles. Chelicerae robust, length of second cheliceral segment including fixed digit 140 (134-146), and movable digit 54 (52-58). Fixed digit bidentate with one large and one small tooth, moveable digit with bidentate tooth. 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 (50) almost as long as movable digit.

Legs (Fig. 4). Excluding ambulacra, lengths of leg I 420 (409-430), leg II 383 (357-402), leg III 338 (315-349), and leg IV 482 (469-489). 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) (as al–ad /av, pd/ pv–pl), 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 distally, 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 spike setae with thickened conical base and rounded tip. Tarsi III, IV with four and three, respectively, distal setae with wide base and flexible filamentous tip. Genu and tibia IV with paired slight ridge anterolateral and posterolateral.

Male and immatures.

Unknown.

Etymology.

This species is named after my daughter Willow Knee. May it inspire her to notice the little creatures as well as the big.

Remarks.

Macrocheles willowae sp. n. is most similar to M. merdarius (Berlese), M. nemerdarius Krantz and Whitaker, and M. pratum sp. n. Macrocheles merdarius is frequently found in litter, manure and compost worldwide, feeding on nematodes and eggs of insects ( Krantz and Whitaker 1988). Macrocheles merdarius has been reported from small mammals, and female mites are often phoretic associates of dung beetles ( Filipponi and Pegazzano 1963, Krantz and Whitaker 1988). Female M. willowae sp. n. differs from that of M. merdarius in the shape of the ventrianal shield, shape of the sternal shield, and length of the arthrodial brush. The anterior margin of the ventrianal shield is more truncated, and the widest part of the shield near JV2 is more angular for M. merdarius than it is for M. willowae sp. n. The posterior margin of the sternal shield is more concave for M. willowae sp. n. The arthrodial brush is almost as long as the movable digit for M. willowae sp. n., and for M. merdarius the brush is approximately half as long as the movable digit. Comparisons were made using the species description for M. merdarius and slide mounted material deposited in the CNC.

Macrocheles nemerdarius was described from the nest of a mouse, Peromyscus in Maryland and the nest of the eastern woodrat Neotoma floridana in Florida, USA, and this species is also phoretic on coprophilous beetles ( Krantz and Whitaker 1988). Female M. willowae sp. n. differs from that of M. nemerdarius in having marginal or submarginal setae slightly longer than dorsal hexagonal setae, posterior margin of sternal shield more concave, pon seta smooth not weakly pilose, j1 only slightly longer than z1 not 1.5 times as long, and J5 slightly shorter than Z5 not half as long as Z5. Comparisons were made using the species description for M. nemerdarius and examination of the holotype specimen loaned from the National Museum of Natural History, Smithsonian Institution.

Female M. willowae sp. n. differs from that of M. pratum sp. n. in having marginal and submarginal setae slightly longer than dorsal hexagonal setae. Genu and tibia IV with slight ridge on anterolateral and posterolateral surfaces in M. willowae sp. n., while M. pratum sp. n. only has a ridge on the posterolateral surface. Seta J5 is slightly shorter than Z5 and more spinose in M. willowae sp. n., J5 is less than half as long as Z5 in M. pratum sp. n. Punctures on the sternal shield are smaller and less prominent in M. willowae sp. n. than in M. pratum sp. n. The ventrianal shield is longer than wide for both species, but the shield is slightly narrower in M. pratum sp. n., ratio of 1.4 compared to 1.3 for M. willowae sp. n.

In Krantz and Whitaker (1988), Dr. W. Yoder provided a short diagnosis and partial illustrations of the female and male of an undescribed and unnamed Macrocheles species collected from Nicrophorus beetles and three mammal species ( Tamiasciurus hudsonius , American red squirrel in Michigan; Tamias striatus , eastern chipmunk in Maryland; and Zapus hudsonius , meadow jumping mouse in Prince Edward Island). This undescribed species was a common associate of Nicrophorus beetles, but it was also found frequently enough on live rodents to suggest an association with small mammals ( Krantz and Whitaker 1988). Dr. W. Yoder reportedly intended to formally describe and illustrate this new species of Macrocheles ; however, to date this species has not been described. Macrocheles willowae sp. n. is likely the same species that Dr. W. Yoder was intending to describe. Over several years, repeated attempts were made to contact Dr. W. Yoder about the status of the description, but contact was unsuccessful.