(figs. 5, 19, 31)
Holotype: soldier, part of lot MZUSP- 4056, 4.i. 1954, R.L. Araujo coll.
Type-locality: Brazil: Minas Gerais State, Belo Horizonte. (20 º 54 ' 36 " S, 47 º W)
Paratypes: BRAZIL: Distrito Federal: Brasília: 1970, K. Kitayama coll. (6996); Fazenda Agua Limpa: 19.ii. 1986, R. Constantino coll. (MPEG- 2622); 4.x. 1999, (UnB- 1890 *); 19.vii. 1981, I. Egler coll. (UnB- 1105); 1.viii. 1982, (UnB- 1109); 1.xi. 1985 (UnB- 1106); 1993, K. Kitayama coll. (UnB- 1107, UnB- 1112); 10.v. 1993, Suzana coll. (UnB- 1120, UnB- 1126); 7.v. 1993, (UnB- 1113); 16.xii. 1993 (UnB- 1114); 28.v. 1993, Carlos coll. (UnB- 1119); 30.ix. 1993, (UnB- 1123); 21.xii. 1992, Marcelo Lima coll. (UnB- 1122); Planaltina - CPAC: 16.iv. 1998, V.S. Dias coll. (UnB- 941, UnB- 943, UnB- 947); Reserva Ecológica do IBGE: 18.ix. 1998, R. Constantino coll. (UnB- 1301). Goiás: Alexania: 25.x. 1973, A.C. Santos coll. (7368); Cristalina: 11.iv. 1991, D. Brandão coll. (UFG- 399); Fazenda São Cipriano: 26.x. 2001, R. Constantino coll. (UnB- 3028); Parque Nacional das Emas: 28.iii- 6.iv. 1984, Exp. MZ-IQUSP coll. (8427); 17, 24.i. 2004, D.A. Costa coll. (12120, 12124); 19, 20, 25.iv. 2004 (12121, 12122, 12123); Pirenópolis: 26.vii. 2004, G.F. Lima Filho coll. (12119). Minas Gerais: Belo Horizonte: 23.viii. 1962, R.L. Araujo coll. (59); 4.i. 1954 (4056, 4058), 29.xi. 1956 (4498 *); 16.viii. 1971 (4935); Bom Sucesso: 12.xi. 1972, (5770); Campos Altos:, 12.xi. 1972 (5877); Campanha: 28.vii. 1954, (4228); Curvelo: 15.ii. 1972, (5084); Lagoa Santa: 3.i. 1957, (4702); Lagoa Dourada: 29.vii. 1975 (6256); Fazenda Susano: 28.x. 2001, R. Constantino coll. (UnB- 3116, UnB- 3150); Fazenda Rossato: 27.x. 2001 (3076); Francisco Sá: 16.vii. 1975, R.L. Araujo coll. (5979); Paraopeba: 14.x. 1993, Terezinha coll. (UFV- 4828); São Sebastião do Paraiso: 23.ii. 1945, R.L. Araujo coll. (4122); Uberlândia: 8.xi. 1972, (5711). São Paulo: Araçatuba: 8.xii. 1953, R.L. Araujo coll. (3991); Campinas: 17.i. 1970 (4751); Novo Horizonte: 24.xi. 1944, R. Araujo & Silva coll. (11357); Pirassununga: 28.ix. 1947, R.L. Araujo coll. (3876); Santo Amaro: 10.x. 1950 (3230); São José dos Campos: 26.v. 1953 (4321); São Paulo (Ipiranga): 6.xii. 1907, Herman Luederwaldt coll. (10822, 10823).
Etymology: mirim (small) from Tupi, a Brazilian Indian language, in reference to soldier size, smaller than most other Orthognathotermes species.
Imago. Eyes small, distant from the inferior margin of head, equal to the larger diameter of the ocellus. Ocelli in dorsal view reniform and narrow, oval and remote from the eye by distance equal to its minimum diameter in lateral view. Fontanelle narrow and small size. Head capsule covered by short hairs, scattered bristles. Labrum with bristles on two rows. Pronotum with short hairs and scattered bristles, mainly on the margins. Mesonotum and metanotum covered by short hairs, concentrated distally and on posterior margins. Head and pronotum sepia brown, tergites brown to pale brown, sternites pale brown to yellow, legs brown to pale brown, wing scales sepia brown.
Comparisons. The imago of O. mirim sp. nov. differs from those of the other species by the combination of small fontanelle and eyes. The most similar species is O. okeyma sp. nov., from which it differs by the labrum with bristles in two rows.
Soldier. Head sides parallel in dorsal view. In profile dorsal lump slightly salient, situated between the flanges. Mandibles of the first pattern, tooth-like projection at proximal half. Head capsule with sparse bristles, short hairs variable, from sparse on entire head capsule to denser only distally, scattered microscopic hairs on all surfaces. Posmentum with bristles and short hairs. Pronotum with bristles and short hairs on the surface, denser at margins. Mesonotum and metanotum with bristles and short hairs on posterior margins. Abdominal tergites densely covered with short hairs and bristles. Sternites covered with short hairs and erect bristles on posterior margins.
Comparisons. O. mirim sp. nov. soldier has a head capsule smaller than all other species of the same mandible pattern and differs from all by the labrum without lobes. The most similar species is O. pilosus sp. nov. whose soldier displays a head capsule covered with denser short hairs.
Geographical distribution. All records of O. mirim sp. nov. are in open formations (Fig. 31).