A new species of rake-legged mite, Caeculus cassiopeiae (Prostigmata, Caeculidae), from Canada and a systematic analysis of its genus
Bernard, Jared
Lumley, Lisa M.
Buck, Matthias
Cobb, Tyler P.
ZooKeys
2020
926
1
23
DE2AB6DE-B683-5DCF-ADA4-A1678DF6EAA5
Bernard & Lumley
Bernard & Lumley
2020
Arachnida
Caeculidae
Caeculus
CoL
Animalia
Caeculus cassiopeiae
Trombidiformes
0
1
Arthropoda
species
cassiopeiae
sp. nov.
Material examined. Holotype.Canada • 1 ♀; Alberta, Medicine Hat, near Gas City Campground; 50°2.23'N, 110°43.56'W; elev. ca 700 m; 26-27 Jul. 2014; M. Buck leg.; yellow pan traps; arid SW slope and adjacent disturbed plain of Agropyron cristatumand Medicago sativa; det. J. Bernard and L. Lumley, 30 Aug. 2016; cleared in 85% lactic acid, dissected, and slide-mounted; PMAE M00019466. Paratype.Canada • 1 ♀; ibid.; stored in 95% EtOH; PMAE M00030967.
Other material. Canada • 8 ♀♀; ibid.; 26 Jun. 2017; L. Lumley leg.; collected with paintbrush; hard dry soil surface; det. L. Lumley; stored in 95% EtOH; PMAE M00030972 to M00030979.
Diagnosis. The five bsetae on the centrodorsal opisthosoma are arranged in an M, three pairs of Ppsetae are aligned on the posterior third of the aspidosoma, and trochanter III has three setae along anterolateral surface.
Female description ( N= 2, all measurements in micrometres, μm). Idiosoma dorsum(Figs 1- 3). 1380-1592 = idiosomal length ( IL); 1.920 xlonger than greatest width (at level of posterior margin of mediodorsal opisthosomal sclerites) (718-829 = IW). Sclerites tawny with pale ridges, ochre to raw sienna between sclerites, translucent white setae (Fig. 1A). All clavate idiosomal setae barbed (Fig. 2C). Rostral region with dark brown anteriorly projecting naso bearing one pair elongated clavate setae Po(74-94, ~0.054 x IL), one median eye immediately inferior to base of naso (Fig. 3A), one pair long, thickened attenuate bothridial seta bo(162-188, ~0.118 x IL) with barbed distal end (Fig. 3C), each inserted in anterolaterally projecting bothridium posterolaterad to median eye. Aspidosoma length 485-560 (0.352 x IL), width 425-491 (0.592 x IW) anterior to eyes, posterior margin of sclerite 309-357 (0.430 x IW); pronounced furrow along length of medial axis containing three or four shallow longitudinal reticulated ridges, anterior furrow width 135-157 (~0.189 x IW), posterior furrow width 102-118 (~0.142 x IW), posterior furrow depth 35-41 (~0.050 x IW); two pairs procurved clavate Pasetae on anterior margin; none or one pair clavate Pmsetae near corners of anterior margin; three pairs clavate Ppsetae medial to eyes on posterior lateral margins, aligned parallel to mid-sagittal plane; area around eyes dark, posterior eyes 1.077 xdiameter of anterior eyes (Fig. 2A), holotype with diminutive fourth Ppseta anterior to other three on right side. Centrodorsal opisthosomal sclerite trapezoidal, length 425-490 (0.308 x IL), posterior margin 477-552 (0.665 x IW); one pair clavate a1setae near anterior margin of sclerite midway between mid-sagittal plane and lateral margins; 2.5 pairs clavate bsetae: b1pair anterior to mid-transverse plane and third of distance between mid-sagittal plane and lateral margins, b2pair posterior to mid-transverse plane and midway between mid-sagittal plane and lateral margins, one unpaired median bsseta present between anterior and posterior pairs, the five setae together forming M-shape; one or two pairs clavate csetae along posterior margin (sometimes c1, always c2) (Fig. 2A). Laterodorsal opisthosomal sclerites each bearing five or six clavate setae in tandem, two ( a2and a3) near anterior margin, one or two bsetae at middle of sclerite (always b3, sometimes b4), and two csetae near posterior margin ( c3and c4); lyrifissure iabetween a3and b3; lyrifissure imbetween b4and c3(Fig. 2A). Mediodorsal opisthosomal sclerites fused, bearing clavate d1, d2, and d3setal pairs, with or without unpaired median clavate dsseta slightly anterior to these; posterior opisthosomal sclerite length 0.161 x IL, bearing clavate e1, e2, and e3setal pairs and unpaired clavate esseta slightly anterior to these; lyrifissure ipnear lateral margin between mediodorsal and posterior opisthosomal sclerites (Fig. 2A). Pluriposterior accessory sclerite bearing three clavate setae, including one unpaired median clavate hsseta (Fig. 2B). Figure 1. Caeculus cassiopeiaesp. nov., female Amicrograph showing coloration Bhabitus illustrating cerotegument texture. Scale bar: 0.5 mm. Idiosoma venter(Fig. 2B). Epimeres black to dark brown, cerotegument tawny, progenital valves dark sienna, aggenital sclerites raw sienna, adanal sclerites brown ochre, pseudanal sclerites raw sienna, translucent white setae. Epimeral setal formula (I-IV) 7-3-4-5. Epimeres I and II fused, anterior margin of epimere I bearing seven clavate setae, most proximal seta slightly less expanded than others and setae get progressively longer distally, distalmost ~76-120 (~0.071 x IL), epimere II with three clavate setae along anterior margin; epimeres III and IV fused (separate from I + II), epimere III with three clavate setae along anterior margin and one clavate seta midway along proximal margin, epimere IV with one clavate seta at anteroproximal margin, one clavate seta on midline a third epimeral length from proximal margin, and three clavate setae along posterior margin (Fig. 2B). Progenital valves ( PG) each with seven smooth acuminate simple setae; aggenital sclerites ( AG) each with three clavate setae; surrounding ventral cuticle bearing nine pairs of clavate setae, including pair ag1between epimeres IV (Fig. 2B). Adanal sclerites ( AD) each bearing two clavate setae; pseudanal sclerites ( PS) each with three clavate setae; one unpaired medial clavate seta posterior to anus; lyrifissure ihlaterad to anterior pseudanal sclerite (Fig. 2B). Figure 2. Caeculus cassiopeiaesp. nov., female idiosoma Adorsum Bventer; PG, progenital valve; AG, aggenital sclerite; AD, adanal sclerite; PS, pseudanal sclerite Cdetail of bsseta, exemplifying typical clavate idiosomal seta. Scale bar: 0.5 mm ( A, B). Gnathosoma(Figs 2B, 3A, B). Palps black, chelicerae dark brown, subcapitulum black to dark sienna, translucent white setae. All clavate setae barbed, all simple setae smooth. Palps ( PA) five-segmented, setal formula, trochanter-tarsus, solenidia ωand eupathidia ζin brackets: 0-2-1-5-10(1 ω+1 ζ); trochanter without setae; femur bearing two dorsal clavate setae midway along length, with proximal seta a third length of distal seta; genu bearing longest subclavate seta on tubercle at distal laterodorsal margin; tibia bearing five setae: one proximal anteroventral barbed spiniform seta, one laterodorsal spiniform seta with barbed distal end, one proximal dorsal elongated clavate seta, one distal dorsal barbed spiniform seta, and one posterolateral clavate seta (Fig. 3A); well-developed tarsus (Fig. 3B) bearing three dorsal smooth acuminate spiniform setae, one elongated spiniform seta with barbed distal end midway on ventral surface, one elongated barbed subclavate seta midway along posterolateral surface slightly distal to a minute solenidion ωrecessed in large receptacle, one anterolateral smooth acuminate spiniform seta a third tarsal distance from distal end, one short smooth acuminate seta at distal posteroventral margin, two simple setae at distal end, and one eupathidium ζposterior to one minute smooth spiniform seta at distal ventral margin. Chelicerae ( CH) each with fixed digit regressed to lobe and movable digit uncinate (Fig. 3A). Subcapitulum bearing two pairs of simple adoral orsetae (Fig. 3A) and two pairs of elongated thickened acuminate simple hypostomal setae mand nalong base of hypostome, mmedial to and slightly longer (53-63, ~0.039 x IL) than n(Fig. 2B). Figure 3. Caeculus cassiopeiaesp. nov., female Aanterodorsal view of rostrum and gnathosoma Bdetail of palp tarsus Cdetail of distal bothridial seta. Abbreviations: CH, chelicera; PA, palp; bo, bothridial seta; d, dorsal; df, reduced fixed cheliceral digit; dm, movable cheliceral digit; ζ, eupathidium; hyp, hypostome; l", posterolateral; ld, laterodorsal; me, median eye; Po, naso seta; ω, solenidion; v', anteroventral; v, ventral; v", posteroventral. Scale bar: 0.1 mm ( A). Legs(Fig. 4). Black with translucent white setae. All clavate setae barbed, all rake/spiniform setae smooth. Formulae of leg setae (including rake setae), trochanter-tarsus, tarsal bothridial setae bt, solenidia φ/ ω, eupathidia ζ, microseta κ", and famulus εin brackets: leg I 5/6-8+3(1 ζ)-21(2 ζ)-22(1 φ+1 ζ+1 κ")-12(1 ω+5 ζ+1 ε); leg II 5-10+4-16-17(1 φ)-14(1 ω+1 ε); leg III 7-5+2(2 ζ)-9(1 ζ)-15(1 φ+1 ζ)-9(1 bt+1 ζ); leg IV 7-2(1 ζ)+3(2 ζ)-9(1 ζ)-13(2 ζ)-13(1 bt+1 ω). Leg I length 1301-1502 (~0.943 x IL; Fig. 4A); trochanter I bearing three procurved clavate setae on tubercles along anterolateral margin, two or three dorsal clavate setae; basifemur I with one rake seta on anteroventral margin and one rake seta on posteroventral surface; telofemur I with one rake seta on anteroventral margin and one eupathidium ζa third the length from distal end on posteroventral margin; genu I with two anteroventral rake setae, one elongated anteroventral subclavate seta near proximal margin aligned with rake setae, three anterolateral clavate setae, one short anterolateral eupathidium ζnear distal margin, five clavate dorsal setae, five posterolateral setae with middle seta elongated subclavate and remainder clavate, one short eupathidium ζnear distal posterolateral margin, five posteroventral setae with most proximal clavate, followed by one rake seta and three elongated subclavate setae; tibia I with four anteroventral rake setae, one elongated spiniform seta near proximal anteroventral margin in line with rake setae, four anterolateral clavate setae, five clavate dorsal setae, four posterolateral clavate setae, three posteroventral rake setae, and one spiniform seta on posteroventral surface proximad to rake setae, and the following three near distal anterolateral margin, most distal to least: one microseta κ", one recessed solenidion φin large receptacle, and one eupathidium ζ; tarsus I bearing four spiniform setae along each anterolateral, posterolateral, and posteroventral margins, one recessed solenidion ωin large receptacle situated a third the tarsal length from distal end on dorsal surface (Fig. 4E), one famulus εmidway along anteroventral surface, and eupathidia ζat the following locations: proximal dorsal surface, midway along posterolateral margin, a tenth the tarsal length from distal end on posteroventral margin, at distal anteroventral margin, and at distal anterolateral margin. Remaining clavate setation for leg I as in Fig. 4A. Chaetotaxy of other legs as in Fig. 4B-D. Basifemur II with one elongated barbed subclavate seta midway along posteroventral surface; genu II with one rake seta a third the distance along posteroventral surface; tibia II with three posteroventral rake setae, one dorsal solenidion φnear distal margin; tarsus II bearing one recessed solenidion ωin large receptacle a third length from distal end on dorsal surface, slightly distal to one anteroventral famulus ε(Fig. 4B). Trochanter III with three anterolateral clavate setae and two or three dorsal clavate setae; tibia III with one solenidion φnear distal margin on dorsal surface (Fig. 4C). Tarsi III and IV each with one elongated smooth slender bothridial seta bta quarter of the length from distal margin on dorsal surface (125-145 [~0.091 x IL] on tarsus III; 143-166 [~0.104 x IL] on tarsus IV); tarsus IV with one solenidion ωa third the length from distal end on dorsal surface (Fig. 4C, D). Tarsal claws on all legs equal in size. Maleand immatures unknown. Figure 4. Caeculus cassiopeiaesp. nov., female A-Ddorsal view of legs I-IV Edetail of solenidion ωon tarsus I. Scale bar: 0.5 mm ( A-D). Abbreviations: ε, famulus; ζ, eupathidium; κ", microseta; φ, tibial solenidion; ω, tarsal solenidion; bt, tarsal bothridial seta; d, dorsal; l', anterolateral; l", posterolateral; v', anteroventral; v, ventral; v", posteroventral.
Etymology. The bsetal arrangement on the centrodorsal opisthosoma resembles the five-star constellation named for Cassiopeia, the vain wife of King Cepheus in Greek mythology. The constellation is also known as the "Celestial M" given its orientation to the horizon when it ascends in the night sky on its arc around Polaris, and is known as the "Celestial W" as it sets. Cassiopeia'srise is most observable in the evenings during northern autumns. The genitive epithet abides by Articles 11.9.1.3 and 31.1.2 of the International Code of Zoological Nomenclature, and hence means "Cassiopeia'srake-legged mite."
Ethology. We observed individuals both walking and motionless with legs I positioned in a raptorial manner above the soil surface. A captive individual consumed a prostigmatan we collected from the same exposed soil.