Heminothrus intermedius, Villagomez & Heethoff, 2024

Villagomez, Fernando & Heethoff, Michael, 2024, Two new species of Platynothrus and Heminothrus (Oribatida: Crotoniidae) from Mexico, Zootaxa 5453 (2), pp. 214-232 : 222-230

Heminothrus intermedius sp. nov.

( Figs. 10–18 , 22–24)

Zoobank code: urn:lsid:zoobank.org:act:D2C94DB6-2112-41F8-93DC-DC877DE2DBCF

Genbank accession numbers: PP234981— PP23498.

Diagnosis. Sensillus short, head rhomboidal, or quite asymmetrical depending on view, smooth; interlamellar seta very long, surpassing insertion of rostral seta, slightly barbed; lamellar setae also long and notably barbed; peripherical notogastral setae long and barbed, mainly at base; with 13 pairs of genital setae; monodactylous.

Description. Measurements in µm. Length 520-570, width 230-260.

Integument. Body color yellowish brown to brown, debris attached to whole body (Figs. 22-23), including prodorsal region and notogaster, most abundant in caudal notogastral region. Cuticular porosity present on epimeral plates towards trochanters, subcapitulum and prodorsum, where overlays with small pits between interlamellar setae insertions (Fig. 24). Notogaster smooth with weakly punctate surface distributed mainly in lateral regions; below lamellar apophysis, less profuse porosity on rostral region, notopleural region less sclerotized and with costate lined pattern. Genital and anal plates smooth.

Prodorsum ( Figs 10 , 12 , 23-24). With some surface lines and muscle sigillae posteriorly, near dorsosejugal articulation. Anteriorly with pair of long apophyses, bearing seta le; each about three times longer than broad and extended posteriorly as surface carina, directed toward insertion of seta in; apophysis connected by distinct transverse ridge. Protruding conical bothridum, with lateral minute process on which exobothridial alveolus (ex) is located (Fig. 24); emergent part of sensillus (ss) short (28), smooth, with rhomboidal or quite bipartite head (Fig. 24); interlamellar seta (in) very long (170), slightly barbed but more conspicuously at base, distinctly surpassing rostrum length; lamellar seta long (155), notably barbed and slightly curved at end; rostral seta short (48), barbed and usually curved inwards.

Gnathosoma ( Figs. 11 , 13, 14 ). Subcapitulum sub-triangular, with one pair of short, barbed hypostomal (h) setae (9), two genal setae present, smooth and setiform, m (8) shorter than a (18). Chelicerae with four and two teeth on fixed and movable digits respectively, setae cha (33) longer than chb (26), both barbed, Trägårdh’s organ wider at base, projecting at middle of chelicera length. Palp medium sized (75), with barbed setae in femora, tibiae, and tarsi, all others smooth, spiniform or setiform. Palpal chaetotaxic formula from femur to tarsus: 1-1-3-7(1).

Notogaster ( Fig. 10-11 ). Flattened, usually mostly covered with attached debris. Fifteen pairs of notogastral setae of different sizes ( Table 2 ): setae in medial region (c 1, c 2, d 2, e 1) inserted without apophysis, all smooth and small, c 1 - c 1 distance wider than d 1 -d 1; peripherical setae with protruding apophysis, all notogastral setae at latero-caudal region long and barbed. Opistonothal gland opening at or slightly posterior to level of f 2 apophysis; h 2 apophysis ventrally inserted; h 3 ventrally inserted on very small apophysis; setae p 1 and p 2 usually curved, their apophyses close to each other, p 3 thinner and less barbed. Lyrifissure ips at similar level than ad 3, ih anterior and at level of e 2 apophysis. Lyrifissures ip, im and ia located in pleural region, only visible in lateral position and, therefore, not illustrated herein.

Epimeral region ( Fig. 11 ). Epimeral setae formula 3-1-3-4. Setae 1a, 1c, 2a, 3a short and spiniform (<8); 1b, 3b and 4b setiform and slightly longer (12); seta 3c (20) longer of all epimeral setae, barbed; setae 4a, 4c and 4d barbed (<14); epimere IV with longitudinal ridge isolating 4d from other setae.

Anogenital region ( Fig. 11 ). 13 pairs of genital setae (20-23), inserted in a row, medial to linear submarginal carina; two pairs of medium sized aggenital setae (28) present, barbed, ag 1 inserted at middle of genital plate and ag 2 near base; three pairs of medium sized adanal setae barbed, ad 1 (23) slightly shorter, thinner, and less barbed than ad 2 (27) and ad 3 (27). Two pairs of very short barbed anal seta (7) inserted in anterior half of anal plate, lyrifissure ian present, anterior to an 2, iad anterior to ad 3 and aligned between ian and ag 2.

Legs ( Figs. 15-18 ). All legs monodactylous. With mixture of thinner and thicker smooth and barbed setiform and semi-foliose setae. Chaetotaxy formula from trochanter to tarsus in legs I to IV (solenidia in brackets): I. 1- 9*-5*(1)-5(2)-26(3); II. 1-9*-5(1)-5(1)-24(2); III. 5*-6-5(1)-4(1)-23; IV. 1-4-5(1)-4(1)-23. Numbers with asterisk denotes that some specimens, and even complementary leg on same individual, can have one extra or fewer setae. Most solenidia medium sized or relatively small. Genu I with medium sized solenidion inserted on small apophysis together with smaller in size dorsal seta; tibia with two medium sized solenidia which can look of different size due perspective, both inserted on small apophysis together with bigger in size dorsal seta; tarsus with three solenidia of different sizes ω 1 and ω 3 longer than ω 2, this latter is smallest solenidion on leg I; famulus setiform, dorsally inserted, very near ω 2 and similar in size or slightly longer, with faintly noticeable rounded head. Leg II genu with small solenidion inserted on less protuberant apophysis, together with larger dorsal seta; tibia with only one solenidion inserted on small apophysis together with larger dorsal seta; tarsus with two solenidia larger than all others on this leg, but medium sized, both associated with thickened setae and inserted on small protuberance. Leg III and IV genu with small solenidion inserted on less protuberant apophysis, together with larger and curved dorsal seta; tibia with only one solenidion inserted on small apophysis together with subequal curved dorsal seta.

DNA intraspecific variation. Six specimens of Heminothrus intermedius sp. nov. from the same population were subjected to amplification and sequencing of the COX-1 mitochondrial marker. Nucleotide pairwise distances from 626 nucleotides revealed an intraspecific difference (K2P) ranging from 0% to 0.81% ( Table 4 ).

Type material. Specimens in plastic vials with 75% ethanol were deposited in the collection of the Senckenberg Museum für Naturkunde Görlitz , in Mesofauna / Oribatida section. Holotype female with catalog number DNR 66731, Santiago Comaltepec, Oaxaca, México. 27.02.2022. Coordinates, 17.588906, -96.399861. Montane cloud forest. Near sendero el Relámpago. Litter samples, Jair Paéz Col. eleven females paratypes with the same data with catalog number DNR 66732.

Additionally, seven female paratype specimens, mounted on slides, with the same data as the holotype and other paratypes, were deposited in the Colección de Collembola de México y Ácaros Edáficos, Facultad de Ciencias, Universidad Nacional Autónoma de México, México, with catalog number FC-UNAM: LESM-AC:OR-011 to FC-UNAM: LESM-AC:OR-018. Information on the holotype also can be accessed on this collection with catalog number FC-UNAM: LESM-AC:OR-010, information of DNR 66732 paratypes are associated with catalog number FC-UNAM: LESM-AC:OR-027 to FC-UNAM: LESM-AC:OR-037, each record is accompanied by a photograph of the specimen .

Etymology. The name of this species refers to its morphology being intermediate between the two previously known species of this genus that have a short and smooth rhomboidal sensillus. Following the rules and recommendations of Art. 31.2 of the international code of zoological nomenclature, the epithet is an adjective in singular nominative according with the second declension and the masculine gender of the genus.

Remarks. There are only two described species of Heminothrus with a notably short sensillus, the new species has intermediate characters regarding this seta, since it has a rhomboidal shape, but is completely smooth, lacking terminal barbs or spines. Heminothrus intermedius sp. nov. can be distinguished from H. minor Aoki and H. papua (Balogh & P. Balogh) in having long and barbed interlamellar seta, while in H. minor the setae are smooth and only “as long as their mutual distance”, and in H. papua they are even smaller. This new species also presents notogastral latero-caudal setae very long, usually reaching two consecutive setae (e.g. setae c 3 reaching seta e 2) and situated in well-developed apophysis, seta d 1 smaller than all others notogastral setae; genital plate with 13 pairs of setae; while H. minor and H. papua shows sensillus rhomboidal with terminal spines and smooth but asymmetrical bipartite respectively, also these two species present all lateral apophysis very small or reduced with their associated setae only reaching next seta in lateral margin; seta d 1 sub equals or longer than c 1 - c 2 setae and genital plate with only 9 pairs of setae.

Despite the availability of some sequences in online repositories, there has been no formal documentation of the intraspecific variation of the COX-1 marker in any species of Heminothrus until now. This represents the first record in this regard, revealing lesser genetic distances within this genus compared to Platynothrus .

Figures

FIGURE 10. Heminothrus intermedius sp. nov. Dorsal view habitus with details on prodorsum and notogaster ornamentation, with setae types and arrangement. Legs and pedipalp excluded. Cuticular porosity and punctate pattern shown in right side of prodorsum. Abbreviations: rostral seta (ro); lamellar seta (le); interlamellar seta (in); sensillus (ss); notogastral setae (c1-3, d1-2, cp, e1-2, f2, h1-3, p1); opistonothal gland opening (gla).

FIGURE 11. Heminothrus intermedius sp. nov. Ventral view habitus with details on gnathosoma, epimeres, genito-anal plates and notogaster ornamentation, with setae types and lyrifissures arrangement. Legs and pedipalp excluded. Cuticular porosity shown in right side of epimeral and genito-anal plates. Abbreviations: hypostomal mentum seta (h); anterior and middle genal setae (a, m); epimeral setae (1a-c, 2a, 3a-c, 4a-d); genital setae (g1-13); aggenital setae (ag1-2); anal setae (an1-2); anal lyrifissure (ian); adanal lyrifissure (iad); adanal setae (ad1-3); notogastral setae (h1-3, p1-3); notogastral lyrifissures (ih, ips).

FIGURES 12–14. Heminothrus intermedius sp. nov. 12. Prodorsal setae; 13. Left chelicera, paraxial view; 14. Right pedipalp, antiaxial view. Abbreviations: interlamellar seta (in); lamellar seta (le); lamellar apophysis (lap); rostral seta (ro); sensillus (ss); cheliceral setae (cha, chb); Trägårdh’s organ (Tg); pedipalp setae (sup, l, d, cm, acm, lt, ul, su); pedipalp solenidion (ω).

FIGURES 15–18. Heminothrus intermedius sp. nov. 15. Right leg I, antiaxial view; 16. Right leg II, antiaxial view; 17. Right leg III, paraxial view; 18. Right leg IV, paraxial view. Abbreviations: legs I famulus (ε); leg solenidia (σ, φ1-2, ω1-3).