Trhypochthonius triangulum, Nakamura & Nakamura & Fujikawa, 2013

Nakamura, K., Nakamura, Y. - N. & Fujikawa, T., 2013, Oribatid Mites (Acari, Oribatida) From Tohoku (Northeast Japan), Collected After A Tidal Wave In 2011, Acarologia 53 (1), pp. 41-76 : 56-59

Trhypochthonius triangulum n.sp.

[Japanese name: Togari-montsukidani] ( Figures 12 – 14 )

Diagnosis — Average body length 587 µm; width 348 µm. Prodorsal surface granulate; notogastral surface postulate of hexagonal pattern. Of all notogastral setae, the longest h 1. Solenidia ’ 1 and σ shorter than each dorsal seta. Genito-anal setal formula: 7-0-1-3. Subcapitulum diarthric, subcapitular setae: 1-1-1. Epimeral setal formula: 3-1-3-3. Homotridactyle.

Material examined — Holotype (Adult female) (NSMT-Ac 13626) from sand, soil and humus at point C; 2 paratypes (NSMT-Ac 13625 and 13627): same data as holotype.

Etymology — After the shape of notogastral posterior region.

Measurements and body appearance — Body length (26 exs.) 464 (587) 629 µm; width (27 exs.): 307 (348) 407 µm. Body colour light yellowish brown. Prodorsal surface granulate; notogastral surface postulate with hexagonal pattern. All specimens female. Percentage of gravid females 89 % in total, having 1 to 4 eggs.

Prodorsum — Triangular in dorsal view ( Fig. 12A ). Rostrum rounded. Setae ro (80 µm) thin, barbed setiform inserting almost mid-distance between rostral anterior margin and insertion of lamellar setae. Setae le (71 µm) and in (95 µm) thick, long, densely barbed bacilliform. Sensilli (61 µm) with spiculate fusiform head and thin stem ( Fig. 12B ). Bothridia cup-shaped, opening dorsolaterally. Setae ex (4 µm) smooth minute cone-like, inserting at the basal portion of bothridium. Relative distances: (in-in: 100 µm)> (le-in: 70 µm)> (le-le: 50 µm)> (ro-ro: 43 µm)> (ro-le: 32 µm).

Notogaster — Notogaster anteriorly straight, posterior angular. Of all 16 notogastral setae including virtual f 1; the longest h 1 (77 µm), the shortest c 2 (18 µm). Setae p of series inserting ventrally ( Fig. 13A ). Lyrifissures ia aligned longitudinally posterior to c 3; im obliquely between e 1 and gla; ip perpendicular to notogastral outline, lateral to f 2; ih obliquely, anterior to cp; ip s ventrally situated at the level of the insertion of setae ad 3. Relative distances: (d 2 - d 2: 177 µm)> (e 1 - e 1: 143 µm)> (e 1 - h 3: 136 µm)> (h 3 - h 3: 121 µm)> (e 1 - f 1: 107 µm)> (h 1 - h 3: 102 µm)> (d 1 - d 1: 98 µm)> (f 1 - f 1: 95 µm)> (h 1 - h 1: 93 µm)> (d 1 - e 1: 88 µm)> (p 1 - p 1: 79 µm)> (c 1 - c 1: 73 µm)> (c 1 - d 1: 54 µm).

Ventral region — Genito-anal setal formula: 7- 0-1-3; all setae thin setiform; genital setae (32 µm) densely barbed; anal (29 µm) and adanal setae (30 – 36 µm) sparsely barbed ( Fig. 13A ). All adanal setae aligned in adanal. Lyrifissures ian and iad aligned obliquely at the level of anal anterior margin. Subcapitulum stenarthric, subcapitular setae: 1-1-1; setae h (13 µm), A (32 µm) sparsely roughened; m (3 µm) smooth, minute cone-like ( Fig. 13E ). Epimeral setal formula: 3-1-3-3; all setae (16 – 32 µm) thin, short, smooth setiform; 1 c the longest; 1 A = 2 A the shortest. Epimeral borders distinct. Cheliceral setae cha (42 µm) long, barbed setiform; chb (17 µm) short, smooth, spiniform. Trägårdh’s organ (29 µm) thin.

Legs — Homotridactylous; claws (43 µm) dentate dorsally ( Fig. 13B ). Setal formula: I (1-5-5-5- 19), II (1-5-5-5-17), III (2-4-3-4-12) , IV (1-2-3-3-10). Solenidiotaxy: I (1-2-3), II (1-1-2), III (1-1-0) , IV (0- 1-0). Measurements (µm) of segments according to holotype: [Right-left] I([50-?]-[86-?]-[41-?]-[27-?]-[66-?]), II ([?-?]-[73-?]-[41-?]-[27-?]-[63-?]),

Acarologia 53(1): 41–76 (2013)

III([46-?]-[63-?]-[36-36]-[27-29]-[63-61), IV([54-50]-[68-63]-[43-41]-[38-39]-[84-80]).

Measurements (average value: µm) of segments according to depressed paratypes: [Right-left] I([47-47]-[79-73]-[46-47]-[31-31]-[54-59]), II([47-39]-[70-71]-[34-43]-[29-36]-[58-54]), III([57-59]-[59-55]-[36-30]-[29-30]-[50-54]), IV([54- 54]-[63-63]-[36-36]-[32-38]-[71-84]).

All legs bearing one solenidia of all tibiae and genua contiguous to dorsal seta ( Figs. 13 C-D). On tarsus I, famulus ε (14 µm) obtuse situated laterally to ω 1; ω 1 (25 µm) thick bacilliform; ω 2 (25 µm) thin setiform inserting near the base of claws; ω 3 (14 µm) situated lateral to famulus and posterior to ω 2. Solenidia ’ 1 and σ shorter than each dorsal seta. On tibia I, solenidion ’ 1 (31 µm) setiform and ’ 2 (6 µm) spiniform, situated on either side of seta d (55 µm) on common apophysis ( Fig. 13C ). On genu I, σ (12 µm) bacilliform, contiguous to barbed ensiform seta d (21 µm) situated on a small apophysis ( Fig. 13D ).

Remarks — The new species is similar in shape of notogaster, insertion of rostral setae, namely, almost mid-distance between rostral anterior margin and insertion of lamellar setae, and length of notogastral setae to Trhypochthoius tectorum ( Berlese, 1896) , T. septentrionalis Fujikawa, 1995 and T. fujinitaensis Fujikawa, 2000 . The chelicerae of the new species are similar in appearance to those of T. semovitussi Szywilewska, 2004 and T. sphagnicola Weigmann, 1997 . However, the new species differs from its conginers in having smaller body size, solenidion ω 1 located between famulus and seta ft ’ on tarsus I, setiform solenidion ω 2 on tarsus I, and sparsely barbed bacilliform dorsal seta on tibia I.

Figures

FIGURE 12: Trhypochthonius triangulum n.sp.: A – Dorsal view; B – Right bothridial region; C – Part of chelisera (A, C: Holotype NSMT-Ac 13626; B, Paratype NSMT-Ac 13625).

FIGURE 13: Trhypochthonius triangulum n.sp.: A – Ventral view; B – Solenidial region on right tarsus I; C – Solenidial region on left tibia I; D – Solenidial region on genu I; E – Gnathosoma (A: Holotype NSMT-Ac 13626; B-E: Paratype NSMT-Ac 13625).

FIGURE 14: Trhypochthonius triangulum n.sp. by the scanning electron microscopy (photos by Nakamura Y.-N., Ohgi Y. and Shirosaki T.): A – Dorsal view; B – Right bothridium.