Dicranocentrus pampaensis Silva, Nunes, Winck & Bellini, 2024, sp. nov.

Dicranocentrus pampaensis sp. nov. Silva & Bellini

Figs 1−7, Table 1

Type material. Holotype: male on slide, Brazil, Rio Grande do Sul State, Jaguarão Municipality (32°32’08.4”S 53°23’51.9”W), Eucalyptus plantation, phytogeographic domain of the Pampa, 01–04/XI/2018, Winck, B. et al. col., pitfall traps. Paratypes: two males and three females, same data as holotype.

Diagnosis. Bluish pigments on Ant. II–IV, anterior head and tibiotarsi. Ant. Ib and IIb ventrally with two smooth chaetae each. Labral papillae apically rounded. Dorsal head lacking A1, S2 and Ps3 mac, with 6–7 posterior mac (in P group), and three interocular chaetae. Maxillary outer lobe basal chaeta acuminate. Basal labial chaeta M1 ciliated, others smooth, labium with four posterior scales. Th. III–Abd. V with several postero-lateral psp each, Th. II–Abd. IV with 12, 9, 5, 2, 2, 5 central mac, respectively, Abd. V with four sens. MTO with about 70 spine-like chaetae. Tibiotarsi I–II without smooth chaetae, tibiotarsus III with a distal one. Tenent hairs capitate; ungues with the internal apical tooth. Ventral tube anterior face with three mac and about 22 ciliated chaetae, lateral flap with about 18 smooth and 29 ciliated chaetae. Tenaculum corpus with a single chaeta. Manubrial plate with 13 ciliate chaetae and nine psp, manubrium ventro-apical region with two ciliate chaetae. Dens proximally with 45–64 spines, distributed in 3–5 rows.

Description. Habitus typical of the genus (Fig. 1). Body length (head + trunk) of holotype = 2.76 mm, range of type series = 2.74–3.60 mm; average body length of adult females = 3.22 mm, average body length of adult males = 2.90 mm, average body length of adults = 3.06 mm. Specimens fixed in 70% ethanol with yellowish background, Ant. I distally, Ant. II–IV, anterior head and distal tibiotarsi dark blue (Fig. 1). Coarsely ciliate scales typical of the genus present on Ant. I, Ant. IIa, head (dorsally and ventrally), dorsal trunk, legs (all segments), anterior and posterior faces of ventral tube, ventral manubrium and ventral dens. Dorsal head and trunk mac, mes and mic ciliate.

Head (Figs 2–3). Antennae shorter than trunk, ratio antennae: trunk = 1.00:1.39 (holotype). Ant. III longer than Ant. IV, antennal ratio Ant. Ia–IV of holotype = 1.0:6.0:2.2:7.2:22.0:10.2. Ant. III–IV annulated, Ant. IV with a ventral subapical bifurcated pin projection (Fig. 2A).Ant. III sense organ with two slightly swollen sensory rods and three surrounding guard sensilla, one of them blunt (Fig. 2B). Ant. Ib and IIb with two ventral smooth acuminate chaetae each (Figs 2C–D). Labral papillae apically rounded, internal ones larger and more oval, external ones smaller, emerging from large cavities (Fig. 2E); labral formula with 4 (a1–2), 5 (m0–2), 5 (p0–2) smooth chaetae, p0 longer than others, a chaetae slender, prelabral chaetae (pl) smooth, larger than labral ones (Fig. 2F). Eyepatch with eight ocelli, A largest, B–F subequal in size, G–H smaller than others, with one mac and two mes as interocular chaetae, without interocular scales (Fig. 2G). Head dorsal chaetotaxy rows with 10–12 antennal (An), five anterior (A0, A2–3, A5–6), 3–5 medial (M0–3, M3i) (M0 present in three specimens); seven sutural (S0–1, S3–6, S6i), two post-occipital anterior (Pa1?, Pa5), one postoccipital medial (Pm2?), 1–2 post-occipital posterior (Pp3, Pp7, the latter also as a mic) and two post-occipital external (Pe2–3) mac, respectively (Fig. 2G). Labium with six papillae (H, A–E), with 2, 0, 5, 0, 4, 4 guard chaetae, respectively, l.p. of papilla E finger-shaped, not reaching the papilla apex (Fig. 3A); labium with five proximal chaetae, an2–3 slightly smaller than the others (Fig. 3B); labial basomedian and basolateral fields chaetotaxy formula as M 1m 2r1–3el1–2/a1–5, with r1 and r3 (rarely absent), and s maller than r2; labium basomedian field with four posterior scales (Fig. 3B). Maxillary outer lobe apical chaeta slightly longer than subapical one, both smooth and acuminate, sublobal plate with four chaeta-like appendages, lateral one reduced (Fig. 3C). Post-labial chaetotaxy with about 41 rough (weakly ciliate) chaetae, three of them along the cephalic groove (Fig. 3D).

Trunk dorsal chaetotaxy (Figs 4 – 5). Th. II–Abd. IV with 12, 9, 5, 2, 2, 5 central mac, respectively, Th. II–Abd. V sens formula as 2,2|1,3,3,+,4, ms formula as 1,0|1,0,1,0,0, bothriotricha formula as 0,0|0,2,3,2,0. Th. II, excluding the anterior collar, with one anterior (a5), five medial (m1–2, m4, m4i, m4p) and six posterior (p1i, p1p, p1–3, p2e) mac, p4–6 as mic (Fig. 4A). Th. III with seven anterior (a1–7), three medial (m4, m6p, m6e) and three posterior (p1–3) mac, at least four psp in the postero-lateral region (Fig. 4B). Abd. I with two anterior (a2–3) and three medial (m2–4) mac; at least five psp in the postero-lateral region (Fig. 4C). Abd. II with three medial (m3–3e, m5) mac; at least seven psp in the postero-lateral region (Fig. 4D). Abd. III with one anterior (a3), two medial (m3, pm6) and one posterior (p6) mac, at least eight psp in the postero-lateral region (Fig. 5A). Abd. IV with five central (A3, A6, B5–6, Be2?) and 7–8 lateral (D3, E2, E4–4p, F1–3, Fe4) mac, as sens antero-internal to A3, at least 12 central long sens, at least five psp in the postero-lateral region (Fig. 5B). Abd. IV 1.40 times as long as Abd. III along dorsal midline (holotype).Abd. V with one anterior (a6e?), three medial (m2–3, m5) and five posterior (p1, p3, p4–5, 5pe) mac, three internal and one lateral sens and at least four psp in the postero-lateral region (Fig. 5C).

Legs (Figs 6A–B). MTO with about 70 smooth spine-like chaetae (Fig. 6A). Tibiotarsi I–II without smooth chaetae, tibiotarsus III with one distal smooth chaeta shorter than tenent hair. Tenent hairs slightly capitate, two small pretarsal chaetae present (Fig. 6B). Ungues with four inner teeth: two subequal paired basal teeth on proximal 1/3, one unpaired median tooth on proximal 3/5 with same size of basal teeth, and a small apical tooth on distal 1/8; unguiculi lanceolate, all lamellae smooth except for the postero-external lamella with a single tooth on its proximal 1/2.

Abdominal appendages (Figs 6C–E, 7). Ventral tube with three distal mac and about 22 ciliate chaetae of different sizes on anterior face (Fig. 6C); about 34 ciliated chaetae and five smooth chaetae on posterior face (Fig. 6D); and about 18 smooth and 29 ciliated chaetae on each lateral flap (Fig. 6E), some chaetae weakly ciliate and almost smooth on some specimens. Tenaculum corpus with a single rough chaeta, each ramus with four teeth. Dorsal manubrium without smooth acuminate chaetae, manubrial plate with 13 ciliate chaetae and nine psp (Fig. 7A), manubrium ventro-apical region with two ciliate chaetae (Fig. 7B). Dorsal dens with one smooth acuminate chaeta on its dorso-proximal region, dens with 45–64 ciliate spines in 3–5 rows in the proximo-medial region (Fig. 7C). Mucronal apical tooth larger than subapical one, spine reaching apex of subapical tooth (Fig. 7D).

Etymology. The species is named after the Pampa biome, where it was discovered.

Habitat. Specimens of Dicranocentrus pampaensis sp. nov. were found in Eucalyptus plantations with a semiopen canopy with considerable input of sunlight. The local altitude is 146 m and the climate is classified as Cfa according to the Köppen classification (Kottek et al. 2006); mean annual temperature and rainfall are 17°C and 1301 mm, respectively. During the sampling days (November 2018), the temperature ranged from 11.4 to 23.6 °C and the precipitation was 9 mm per day, while in October 2018, the accumulated precipitation was 100 mm. The soil of the area is an Ultisol (24% clay, 16% silt and 60% sand) with carbon content of 1.6 g /kg and average bulk soil density of 1.24 g /cm 3 in the topsoil layer (0-30 cm). The litter layer covers more than 95% of the soil surface with a thickness of ~ 10 cm. The understory plant richness was of four species per square meter.

Remarks. As said before, Dicranocentrus pampaensis sp. nov. belongs to the gracilis -group of species due to the presence of P mac and absence of A1, S2 and Ps3 mac on dorsal head (Mari-Mutt 1979b; Bellini et al. 2020). Within the gracilis -group, Dicranocentrus pampaensis sp. nov. is unique especially by combination of the following characters: its colour pattern; two smooth acuminate chaetae on Ant. I and II ventrally each; chaetotaxy of labial base, dorsal head and trunk; about 70 spine-like smooth chaetae on MTO; and 45–64 spines on dens.

Considering the Neotropical fauna of the gracilis -group, the new species is similar to D. capitaneus Mari-Mutt, 1985, D. colombiensis Mari-Mutt, 1979 in Mari-Mutt (1979b), D. heloisae and D. platensis (Izarra, 1972) in the presence of scales on the labial basomedian field, external rounded labral papillae apically, dental spines and chaetotaxy of dorsal trunk. However, D. pampaensis sp. nov. can be separated from them especially by: Ant. I and II with two ventral smooth chaetae each (8 and 6 in D. heloisae); presence of three interocular chaetae (4–5 in D. capitaneus); labial r1 chaeta smooth (ciliated in D. platensis); labial basomedian field with 6–8 chaetae (9–11 in D. capitaneus), and 4 basal scales (5–8 D. capitaneus, 6 in D. colombiensis, and 5 in D. heloisae); labral internal papillae apically rounded (acuminate in D. colombiensis, D. heloisae and D. platensis); dorsal head with 6–7 posterior mac (3–5 in the other species); Th. II with 12 central mac (13 in D. capitaneus and D. heloisae); Abd. III with two central mac (three in D. capitaneus); trochanteral organ with about 70 spine-like chaetae (about 100 in D. capitaneus and D. heloisae); tibiotarsi without smooth chaetae other than the apical one on the tibiotarsus III (present in D. heloisae); and ungues with the apical tooth (absent in D. colombiensis). Further comparisons between the Dicranocentrus species from the gracilis- group are presented in Table 1 and in the identification key.

? ? ? 5 ? ? ? ? ? ? ? + 4 12 7 4 2 2 4 ? ? ? ? ? ? ? ? ?

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? ? ? ? ? ? ? 6 + ? ? - 5 12 8 5 2 2 5 ? ? ? - A - - ±77 5–6

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+ ? ? ? C C S 6 4 A R - 4 12 9 5 2 2 5 - - ? - A/P + - ±60 4–5

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? ? ? ? C C S 6 - A A - 10 11– 12 9 4 2 2 2–3 ? ? ? - P - - - -

Data based in: main bibliography: 1 Wahlgren (1908); 2 Schött (1927); 3 Handschin (1929); 4 Yosii (1961); 5 Mari-Mutt (1979b); 6 Jacquemart (1980); 7 Mari-Mutt & Bhattacharjee (1980); 8 Mari-Mutt (1981a); 9 Mari-Mutt (1981b); 10 Mari-Mutt (1981c); 11 Arlé & Mendonça (1982); 12 Mari-Mutt (1983); 13 Mari-Mutt (1985); 14 Xisto & Mendonça (2014); 15 Xisto & Mendonça (2016); 16 Xisto & Mendonça (2017); supplementary bibliography: 17 Schött (1893); 18 Izarra (1972). Legends: (ten.) tenaculum; (+) present; (-) absent; (±) approximately; (/) or; (?) unknown/unclear; (≤) up to; (S) smooth; (C) ciliate; (A) acuminate; (P) capitate; (R) apically rounded; (*) Dicranocentrus longicornis (Carpenter, 1916) dorsal head macrochaetotaxy was based on its similarity with D. gracilis Schött, 1893 and D. schoetti Mari-Mutt, 1979 in Mari-Mutt (1979b), as noted by Mari-Mutt (1979b, pg. 55); (**) including Pa5; (***) other than the distal one on the tibiotarsus III; (****) Dicranocentrus bidentatus Mari-Mutt, 1983 lacks both the apical and medial internal teeth on the ungues.

The presence of M0 mac on dorsal head of some specimens (3) of Dicranocentrus pampaensis sp. nov. type series is a rare condition within the genus. Within the gracilis -group, it was also recorded only in D. edicitae Jacquemart, 1980 from Peru. Even so, the new species differs from D. edicitae in: presence of dark pigments on antennae, frontal head and tibiotarsi (vs. specimens depigmented in D. edicitae); dorsal head P group with 6–7 mac (vs. 4); and Th. III, Abd. I and Abd. IV with 9, 5, 5 mac respectively (vs. 7, 4, 4). It is worth noting that the original description of D. edicitae lacks many important details used in the taxonomy of Dicranocentrus (Jacquemart 1980), making its redescription urgent to a better understanding of its morphology.