Rostrozetes achilles Bomfim, Delabie & Oliveira, 2024, sp. nov.
Creators: name: Bomfim, Grecilane S.
name: Delabie, Jacques H. C.
name: Oliveira, Anibal R.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Sarcoptiformes
Haplozetidae
Rostrozetes
Rostrozetes achilles

description: Rostrozetes achilles sp. nov.
(Figs. 1–7)
Diagnosis. Female. With most of the of Rostrozetes’ characters presented by Sellnick (1925), Beck (1965) and Subías and Shtanchaeva (2023). Red-brown, foveolate. Rostral seta (ro) thin and smooth, smaller than lamellar (le) and interlamellar (in), stronger and barbed. Sensillus (ss) clavate. Notogaster with four pairs of almost longitudinal elevated bands, with the internal one connected anteriorly and posteriorly, forming a pygidium. Twelve pairs of notogastral* setae variable in size and shape, with da, dm and dp large, thick and clavate. Four pairs of saccules, with Sa, S2 and S3 opening on protuberances. Epimeral setation 3–1–2–2. Discidium petal-shaped. Five pairs of genital setae. *Although the opposition among 13–14 versus 10–11 pairs of notogastral setae may cause doubt on the generic affiliation for the new species in step 16 of the key for Haplozetidae genera in Subias and Shtanchaeva (2023), it is important to note that some Rostrozetes, e.g. R. pseudofurcatus Balogh & Mahunka, 1968 —see Remarks), may also have 12 pairs of heteromorphic notogastral setae, while the genus alternatively achieved in the key, Rostrozetella Mahunka, 2006, with three species described (Subías 2024), has 14 pairs of long, not heteromorphic notogastral setae.
Dimensions. Body length (n= 5 females measured) 380−410 µm and width 258–283 µm.
Integument. Cuticle red-brown, highly sclerotized, mostly foveolate, moderately covered with a gel-like cerotegument. Notogater completely covered with small, round and well apart foveolae. Ventral region fully covered with foveolae, except in the anterior ventral plate, around the aggenital setae (ag). Foveolae well apart, round to oval in shape, smaller in coxisternal region, larger in ventral plate (Figs. 4, 5B, D). Genital plate with small foveolae, mostly elongated longitudinally (Figs. 4, 5E). Anal plate with small, mostly round foveolae (Figs. 4, 5B, F). Mentum covered with small foveolae (Figs. 4, 5 C, 7A). Legs mostly smooth, except for femur I and ventral blade-like projections on femora II, IV and trochanter IV, partially covered with large, round foveolae on their antiaxial laterals (Figs. 3, 5A, B, D, 7D–G).
Prodorsum. Mostly convex. Rostrum flatter in lateral view, rounded frontally in dorsal view. Lamella (lam) (Figs. 1, 2A, B, 3A, B) running forward as a lateral ridge connecting the bothridium (bo) to seta le, projecting as a sharp antiaxial tooth, the ‘ dens lamellarius’ (d.lam.) (Figs. 1, 2A, B, 3A, B), laterally to le in dorsal view. Sublamella (sl) (Fig. 3A) poorly developed, united with the lamella close to the bothridium in lateral view. Prolamella (prl) (Fig. 3A, B) forming a rostroventral carina connecting le to ro. Its rostral end, together with the tutorium (tu), (Figs. 3A, B) projects as a round antiaxial tooth, the ‘ dens tutorius’ (d.tut.) (Figs. 1, 2B, 3B), laterally to ro in dorsal view. Tutorium formed by two main lateral carinae beginning somewhat below the bothridium. The upper carina (u.c.) runs anteriorly, about parallel to lamella, to the d.tut., and the lower carina (l.c.) (Figs. 3A, B) runs ventrally, diverging from the upper, to the level of acetabulum I. Bothridium annular (Figs. 1, 2C, 3A), opening laterally. Rostral setae 18−23 μm, (Figs. 1, 2B, 3B) thin, smooth, bent medially, inserted laterally on the rostral tectum somewhat anteriorly to the d.tut., distance between ro −ro insertions ~30 μm. Lamellar setae 48−63 μm, (Figs. 1, 2A, B, 3A, B) strong, finely barbed, bent medially, inserted laterally at the end of the lamella somewhat anteriorly to the d.lam., distance between le −le insertions ~75 μm. Interlamellar setae 60−75 μm, (Figs. 1, 2A, B, 3A, B) strong, finely barbed, bent medially, inserted anterolaterally next to the dorsosejugal furrow (dsj) (Figs. 1, 2A, 3B), distance between in −in insertions ~105 μm. Sensillus ~65 μm, (Figs. 1, 2C, 3A, B) projecting dorsolaterally from bo, with a bristled clavate head in the apical 1/3 of its entire exposed length, distance between ss −in insertions ~80 μm.
Notogaster. Mostly convex, longer than wide, separated from prodorsum by the dsj, (Figs. 1, 2A, 3B), which flexed anteriorly in three arches and connects backward with the hinge of the movable, triangular pteromorph. With four pairs of longitudinal, curved elevations bilaterally distributed as an internal (i.b.), a middle (m.b.), a lateral (l.b.) and an external (e.b.) band, (Figs. 1, 2A, 3A, B, 6A–C) with the i.b. and m.b. located, respectively, medially and laterally to setae da, dm and dp, and the l.b. and e.b. closer to the edge of notogaster. The i.b. are flexed out and connected anteriorly, between setae da, and posteriorly, forming a pygidium (pg) (Figs. 1, 2A, D, 6B, C) between setae h1. The m.b. are slightly flexed out, diverging diagonally backward from the level of setae c2 to the level of saccules s2, where it forms an angle inward to connect the posterior portion of the band with the pg. The l.b. are twice-flexed, running backward laterally from the level of setae c2 to the level of saccules s2. The e.b. are flexed out, running backward accompanying the edge of notogaster from about the level of setae la to the pg. With 12 pairs of setae variable in size and shape (Figs. 1, 2A, 3A,). Centrodorsal setae large, da <dm <dp, thick, clavate smooth at the base and ciliate from the middle to the end. Distances between da −da insertions ~50 μm, dm −dm and dp −dp ~95 μm. Anterolateral setae c2 ≅ la ≅ lm medial to pteromorph, large, smooth and setiform, lm curved inward. Posterolateral setae h1 ≅ h2 <h3, small, smooth and setiform, h1 curved inward. Posteromarginal setae p1 ≅ p2 ≅ p3, minute, smooth and setiform, curved downward. Distance between p1−p1 insertions ~50 μm. Four pairs of saccules, sa, s1, s2 and s3, present, (Figs. 1, 2A, D, 3A) with sa located on band l.b., anterior to setae la, s1 and s2 on band m.b., lateral to setae da and dp, respectively, and s3 on band e.b., dorsolateral to seta p1. All saccules, except s1, opening at the top of three protuberances localized near setae la, dp and p1, respectively. Opisthonotal gland opening (gla) and lyrifissures ia, im, ip, ih, and ips discrete, generally difficult so see due to the foveolate, highly sclerotized cuticle (Fig. 1).
Ventral region. Mostly convex, longer than wide.All setae similar in size and shape, small, smooth and setiform. Epimeres delimited by well separated apodemes. Epimeral setation 3-1-2-2, with setae 1a, 1b, 1c, 2, 3a, 3b, 4a and 4b. Seta 3a anterior the genital aperture. Discidium (dis) (Figs. 4, 5A, B, D, 6D) inserted into a cuticular tuberosity ventral to acetabulum IV, projected ventromedially, in direction to seta 4b, as a smooth, petal-shaped, cuticular free lamina, that revels a glass-like reflective nature when backlighted. Distance between genital and anal apertures about twice the length of genital plate. Genital plate medial to epimeres III and IV, about pentagonal, slightly wider anteriorly (Figs. 4, 5B, E, 6D). Five genital setae present (g1, g2, g3, g4 and g5), with g1–g3 inserted anteriorly and g4–g5 posterior in each valve. Aggenital seta approximately at middle distance between anal and genital plates. Anal plate subquadrate (Figs. 4, 5B, F). Two anal (an1 and an2) and three adanal (ad1, ad2 and ad3) setae present, with ad1 posterior, ad2 posterolateral and ad3 anterolateral to the anal aperture. Lyrifissure iad parallel to lateral margin of anal aperture and medial to seta ad3 (Fig. 4).
Gnathosoma. Subcapitulum diarthric (Figs. 4, 5B, C, 6D, 7A), with pantelobasic rutellum. Subcapitular setae (a, m and h) smooth. Setae a <m, setiform, ~14 and 6 each, h minute, spine-like, ~2 μm. Palp setal formula (from trochanter to tarsus) 0–2–1–3–9 (Fig. 7C), plus solenidion ω. Eupathidium tarsal acm fused with ω forming a ‘double horn’. Chelicera with digitus fixus and mobilis with three teeth each (Fig. 7B). Two barbed and setiform cheliceral setae present (cha> chb, ~20 and 10 μm each). Trägardh’s organ (trg) conic, diagonal to axis of chelicera.
Legs. Basal articles with porous areas present on their paraxial faces (Figs. 7D–G), and provided with a protective fitting (femur I) or ventral blade-like projections (femora II, IV and trochanter IV) that cover weaker parts when legs are flexed (Figs. 3, 5A, B, D, 7D–G). Femur IV with a dorsal tooth, as in some other Rostrozetes species (Beck 1965). Setal formulae from leg I to IV (Figs. 7D–G, Table 1) (solenidia in parenthesis, famulus in brackets): trochanter 1-1-2-1, femur 5-5-3-2, genu 3 (1)-2 (1)-1(1)-2, tibia 4 (2)-4 (1)-3 (1)-3 (1), and tarsus 19 (2) [1]-15 (2)-15-12. Leg I famulus (ε) short, capitate. Lyrifissure ly at base of tarsus I–IV, near arthrodial membrane slightly to antiaxial side. Pretarsi monodactylous, empodial claw falsiform, with one (or exceptionally two) small tooth anteriorly in the basal third.
Males and immature stages. Unknown.
Etymology. The species name was inspired in the Achilles’ heels figure proposed in Walter and Proctor (1999) for armored mites’ legs as weak points in their defense, referring to the apparent use of the discidium in R. achilles sp. nov. to protect its ‘heel’, the joint between tarsus and pretarsus, during leg IV flexion.
Material Examined. Fifty-one females collected from nests of Camponotus cingulatus (Formicidae) in dry cacao fruits and surrounding soil–litter from a cacao plantation at the campus of UESC (14°47’49”S, 39°10’23”W), Ilhéus, BA, Brazil, in 29-VII-2021 and 4-IV-2022 by Grecilane S. Bomfim. Holotype (in a cavity slide with glycerin) and 50 paratypes (5 as above, 2 dissected in slides with Hoyer’s, 32 dehydrated in stubs, and 11 fixed in 70% ethanol) deposited in the Acarological Collection of UESC.
Remarks
Except for Rostrozetes sexclavatus Sellnick, 1925 sp. inq., which lacks a formal description, R. achilles sp. nov. differs from all other species of the genus by the presence of a pair of elevated notogastral bands (i.b.) internal to centrodorsal setae da, dm and dp, which are connected anteriorly between setae da, and posteriorly forming a pygidium. Rostrozetes achilles n. sp. is the sixth species of the genus reported so far as having heteromorphic notogastral setae, and, except for R. perezinigoi P. Balogh, 1995, the thickness of all centrodorsal setae (da, dm and dp) is a feature shared with R. dimorphochaites Higgins, 1966, R. heterotrichus Pérez-Iñigo & Baggio, 1991, R. pseudofurcatus Balogh & Mahunka, 1968, and probably with R. sexclavatus, mentioned by Sellnick (1925) as having 6 clavate setae on hysterosoma. Although a pair of posterior notogastral protuberances is a feature also shared by R. dimorphochaites, R. heterotrichus, R. pseudofurcatus and R. achilles sp. nov. (associated with saccules s 3 in the last one), the new species can be distinguished from them by its larger size (minimum of 380 μm in length vs. maximum of 336 μm in R. heterotrichus). Specifically, it can be distinguished from R. dimorphochaites by the number of notogastral setae (10 vs. 12 in the new species), from R. pseudofurcatus by the number of genital setae (4 vs. 5) and shape of da, dm and dp (bifurcate vs. clavate), and from R. heterotrichus by numbers of both the notogastral and genital setae (11 and 4 vs. 12 and 5, respectively).
The role of the discidium, as well as many other superficial cuticular structures on the lateral body of higher oribatid mites, is probably related to defense. They protect certain parts of the legs or provide a fixed structure against which a leg can fit when it is retracted in a defensive posture or thanatosis. The most developed and diversified forms of discidium among oribatid mites are found in Rostrozetes (Grandjean 1936, 1952, Beck 1965). In specimens of R. achilles sp. nov. frozen alive to induce their defensive behavior before analysis, the laminar discidium appeared to cover the articulation between tarsus and pretarsus during the leg IV flexion close to the body, while other leg joints were covered by the ventral, blade-like foveolate projections of the trochanter and femur. Although this observation corroborates the expected protective nature of the discidium, it is also possible that it may work as part of a locking system operated with the leg IV claw, although the claw may have come loose from the discidium during preparation/observation of the specimens.
Other specialized functions of the discidium in Rostrozetes deserve to be investigated, considering the distinctive structure of it in R. achilles sp. nov. It is a smooth, thin, transparent, glass-like reflective laminar projection, of a different composition from the surrounding cuticle, and such a distinctive structure may be expected to have a specialized function. Considering its position close to the tracheal opening on acetabulum III and its fine, blade-like shape, it is possible that it can affect under-water respiration by assisting, for example, in holding/anchoring a plastron—a thin film of air attached to the body wall (Marx & Messner 2012). Such a function has been suggested for many of the small projections, as tubercles, enantiophysis etc., that are associated with body depressions or grooves that are near tracheal openings in oribatid mites (Pfingstl & Krisper 2014, Behan-Pelletier & Lindo 2023). Even in terrestrial species a temporary plastron might be important during local flooding (Zinkler 1999). The impressive variation in both shape and size of the discidial blade in the congener, parthenogenetic species Rostrozetes ovulum (Berlese, 1908) (see Beck 1965), as well as its ability to survive long-term submersion in water (Pequeno et al. 2021), reinforce this possibility. The fact that R. achilles sp. nov. is also probably parthenogenetic, once no males were found among so many females examined, is another aspect that draws attention among the similarities between those species.
No information is available about the ecology of the mite, and a little more on the host ant (C. cingulatus) which is a common species in the cocoa fields in the region of the study (Delabie et al. 1991, Majer et al. 1994). This ant is a polydomous species (the population of a single colony is distributed in several nests apparently independent) which uses to nest as well in hanged and fallen dry cocoa pods as in any available cavity on a tree or on the ground in a plantation (Delabie et al. 1991).
description: Published as part of Bomfim, Grecilane S., Delabie, Jacques H. C. & Oliveira, Anibal R., 2024, A new species of Rostrozetes (Acari: Oribatida: Haplozetidae) from Brazil, pp. 205-217 in Zootaxa 5556 (1) on pages 206-215, DOI: 10.11646/zootaxa.5556.1.15, http://zenodo.org/record/14595122