Phyllochthonius ovatosetosus, Fuangarworn, Marut, 2010

Fuangarworn, Marut, 2010, Two new species of the oribatid mite genus Phyllochthonius Travé, 1967 (Acari: Oribatida: Phyllochthoniidae) from Thailand, Zootaxa 2521, pp. 26-36 : 27-30

Phyllochthonius ovatosetosus n. sp.

( Figs. 1–4 )

Adult female. Dimensions (n=5). Body length 254 (250–260). Body width (at level of setae cp) 160 (150– 175). Color pale yellow. Setae usually with adherent soil particles.

Prodorsum. Triangular in outline, posterior portion much narrower than anterior margin of hysterosoma. Integument weakly sclerotized, surface smooth. Rostrum extended and pointed, with irregular teeth laterally. Area between interlamellar setae (in) elevated except for concave anterior portion. Rostral (ro), lamellar (le), and anterior exobothridial setae (exa) plate-like, with foveate patterns. Of these, le largest; ro with pointed process, their shape depicted in Figs. 1 A and 1C. Setae exa situated at normal position but extensively developed, forming lobes able to cover nearby bothridium. Posterior exobothridial setae (exp) minute, spinelike. Setae in ovate, 22 long, 12 wide, covered by inconspicuous barbs, foveae absent. Bothridia prominent; sensilli long, flagelliform and barbed ( Figs. 1 A &1C, ss).

Notogaster. In dorsal view ( Fig. 1 A), anteriorly truncated with parallel sides; posteriorly rounded beginning behind level of setae cp. In lateral view ( Fig. 1 C), anterior portion slightly arched, becoming strongly arched posteriorly. Integument smooth and weakly sclerotized, with two transverse scissures: anterior one located behind setal row c, posterior one located in front of setal row e. Sixteen pairs of notogastral setae present, widely spaced. Setae c1, c2, c3, cp, d1, d2, e1, e2, f1, and f2 phylliform or plate-like with foveate patterns; setal rows h and ps simple, setiform. Setae c1 subrectangular, all sides concave, with rounded corners; setae c2 much longer than wide, reaching posterior notogastral scissure. Setae c3 and cp located on tubercles and exhibit mixture of reticulate and foveate patterns, their shape depicted in Figs. 1 A and 1C. Setae e1 broadly phylliform, originating on tubercles and permanently erect, their margin slightly bent downward. Setae e2 elongate, basally round and distally narrowed. Setae f1 elliptical, located in depressed region of cuticle. Setae f2 basally broad and distally tapered, forming long acute process. Setae h1–3 situated on venter: h1 largest, thicker basally than distally; h2 and h3 simple, setiform. Setae ps1–ps3 simple and setiform, situated on venter; ps1 thicker and longer than others.

Venter ( Fig. 1 B). Except for epimeres, ventral surface apparently soft, without plates or sclerotized shields. Genito-aggenital and ano-adanal region delimited by folds of integument. Genital valves with ten pairs of simple setae. Three pairs of genital papillae present. Ovipositor with simple (uncounted) eugenital setae. Anal region with three pairs of anal setae (an), one pair of peranal setae (pa) and three pairs of adanal setae (ad). Epimeral setae minute, setation: 3-1-4-3.

Gnathosoma. Subcapitulum ( Fig. 2 A) with three pairs of setae (a, m, h); all setifom with sparse barbs. Rutellum relatively broader distally; with five distal and one basal tooth. Adoral setae (or1, or2, or3) on lateral lips heteromorphic: or1 vestigial, or2 distally broad and flattened, or3 setiform. Sclerotized pharyngeal cupola (capitular apodeme) present and well developed. Palpi five-segmented ( Fig. 2 C); setation: 0-2-1-2-9; palpal tarsi terminate with forked eupathidium; solenidion ω baculiform, originating proximally and about as long as tarsal segment. Probable setal homologies indicated in Fig 2 C. Chelicerae ( Fig. 2 B) chelate-dentate, relatively slender distally; cheliceral setae cha minute; cheliceral setae chb much longer and setiform.

Legs. Leg IV longest; all bidactyl. Leg I–IV setation (from trochanter to tarsus, famulus included) as follows: leg I (0- 3 -5-6-21); leg II (1-3-5-5-17); leg III (2- 2-4-4-16) and leg IV (2- 2-4-4-14). Solenidial formulae (from genu to tarsus) as follows: leg I (2-1-3); leg II (1-1-2); leg III (1-1-0) and leg IV (1-1-0). Setae d on femora I–II, genua I–II and tibiae I–II, setae l” on genua I–II, setae ft” on tarsi II, and setae ft’ on tarsi III–IV broadly phylliform with foveate patterns. Setae d on femora III–IV, genua III–IV, and tibiae III–IV also broadly phylliform but without foveate patterns (with sparse barbs instead). Solenidia baculiform, famulus clavate with single short lateral bract. Positions of solenidia and probable setal homologies illustrated in Fig 3 .

Males. Apparently parthenogenetic species— males absent among specimens collected. Immatures. Dimensions. Larva (n=3), 163 long, 105 wide; protonymph (n=2), 170 long, 110 wide; deutonymph (n=2), 225 long, 158 wide; tritonymph (n=2), 150 long, 250 wide. Larva white; protonymph to tritonymph white to pale yellow.

Prodorsum. Larva ( Fig. 4 A) and nymphs similar to adult in species-specific characters but differ from adult in having lesser degree of sclerotization and less well-developed prodorsal setae.

Notogaster. Larva ( Fig. 4 A) with narrowed and elongate notogastral setae c1, c2, d1, and d2, all without foveae but with sparse barbs distally; all increasing in size and becoming totally foveate in protonymph. Setae c2 reaching posteriorly to level of setae d 2 in tritonymph. Setae c3 and cp broadly plate-like with foveae from larva. Setae e1, e2 and f1 short, phylliform, with sparse barbs (foveae absent) from larva, becoming foveae in protonymph. Setae f2 located on ventral side in larva ( Fig. 4 B), basally broad and dramatically tapered in distal half. Larva with four pairs of setae h of which h1 remarkably thickened.

Venter. Larva ( Fig. 4 B) bearing Claparède’s organ with stalk and globular head behind epimere I. One pair of bulges present behind epimere IV. Epimeral setation (I–III for larva and I–IV for nymphs) as follows: larva (3-1-2), protonymph (3-1-3-1), deutonymph (3-1-4-2), tritonymph (3-1-4-3); epimeral setae 1c in larva modified as scale. Genital setation (protonymph to tritonymph): 1-4-7. H and PS segments in larva each with four pairs of setae of which most distal pairs (inguinal setae: h4 and ps4) lost in subsequent instars. AD segment added in protonymph with three pairs of setae, AN segment added in deutonymph with three pairs of setae. PA segment added in tritonymph without setae (but one pair of peranal setae added in adult); tritonymph finally with three pairs of setae an, ad, ps and h. Development and arrangement of these setae illustrated in Fig. 4 C–E.

Gnathosoma. Palpal setation (trochanter to tarsi): larva, 1-1-2-9(ω); protonymph, 1-1-2-9(ω); deutonymph and tritonymph, 2-1-2-9(ω).

Legs. Larva with three pairs of legs, all monodactyl. Protonymph to tritonymph with four pairs of legs. In protonymph, all legs monodactyl. In deutonymph, leg I–III bidactyl but leg IV monodactyl. In tritonymph, all legs bidactyl. Leg I–IV setation (trochanter to tarsus, famulus included) as follows: larva: I (0- 2 -3-5-17), II (0- 2 -3-5-15), and III (0- 2 -2-4-14); protonymph: I (0- 2 -4-5-20), II (0- 3 -3-5-15), III (1-2-2-4-14), and IV (0-0-0-1- 7); deutonymph: I (0- 2 -4-6-20), II (1-3-3-6-17), III (2-2-2-4-16), and IV (1-1-3-4-13); tritonymph: I (0- 3 -5-6- 21), II (1-3-4-6-17), III (2-2-2-4-16), and IV (2- 2-4-4-14). Solenidial formulae (genu to tarsus) as follows: larva, I (2-1-1), II (1-1-1), and III (1-1-0); protonymph, I (2-1-2), II (1-1-2), III (1-1-0), and IV (1-0-0); deutonymph, I (2-1-2), II (1-1-2), III (1-1-0), and IV (1-0-0); tritonymph, I (2-1-3), II (1-1-2), III (1-1-0), and IV (1-1-0). No genual or tibial solenidia coupled with respective setae d. Famulus of all instars similar to that of adults. Ontogeny of specific setae and solenidia presented in Table 1.

Material examined. Female holotype (in alcohol, CUMZ-AC2010.18), Salaloy Subdistrict, Tharua District, Ayutthaya Province, Thailand (14°31'48.84"N, 100°42'5.38"E); ex. sandy soil at 0–30 cm depth from riparian zone of Pa-Sak River; 29-IV-2007; leg. M. Faungarworn (Field No. MF 2007-22,). Twenty paratypes, adult and immature, (CUMZ-AC2010.19–38) with same data as holotype. Holotype and fourteen paratypes deposited in the Acari collection of Chulalongkorn University Museum of Natural History, Bangkok, Thailand. Three paratypes deposited in the Acarology Laboratory at Museum of the Biological Diversity of the Ohio State University, Columbus, Ohio; three others in the Hungarian Natural History Museum, Budapest.

Distribution. Known only from its type locality — Ayutthaya Province, Central Thailand.

Etymology. The Latin prefix of the specific epithet refers to the oval shape of the interlamellar setae (ovatus: Latin, oval).

Remarks. Phyllochthonius ovatosetosus n. sp. is superficially remarkably different from the only other nominal species, P. aoutii Travé, 1967 . However, they are considered to be congeneric based on the fixed, permanently erect notogastral setae e1, the interlamellar setae which lack foveae (hence, a different type from other prodorsal setae), and the spine-like posterior exobothridial setae exp. In Atopochthonius and Pterochthonius , the latter two setae are similar to other prodorsal setae, being foveate. Except for size, notogastral setae of P. aoutii and P. ovatosetosus n. sp. are similar. Setae c1, for example, are subsquamous with concave sides, setae c2 are elongate, reaching the posterior notogastral scissure, and setae f2 have an acute process. The different in degree of expansion of these setae is not enough to exclude the new species from the genus Phyllochthonius .

Phyllochthonius ovatosetosus n. sp. differs from P. aoutii in the presence of short and ovate interlamellar setae, much lesser expansion of notogastral setae, ten pairs of genital setae, cheliceral setae cha, a basal tooth on the rutella, the foveate-phylliform shape of setae ft” on tarsi II–IV, and the barbed-phylliform shape of setae d on femora, genua, and tibiae of leg III–IV as well as the absence of solenidia on tarsi III. In P. aoutii , the interlamellar setae are elongate, longer than the distance between their bases (in–in); the notogastral setae are extremely expanded; eight pairs of genital setae are present; cheliceral setae cha are vestigial and there is no basal tooth on the rutella; setae ft” on tarsi II–IV are broadly barbed and setiform, and setae d on femora, genua, and tibiae of leg III–IV are barbed and setiform; a solenidion is present on tarsi III as well.

Figures

FIGURE 1. Phyllochthonius ovatosetosus n. sp., female. A, dorsal view; B, ventral view; C, lateral view (legs mostly omitted).

FIGURE 2. Phyllochthonius ovatosetosus n. sp., female. A, subcapitulum (distal segments of palps omitted); B, chelicera; C, palp (left, abaxial aspect).

FIGURE 3. Phyllochthonius ovatosetosus n. sp., female. A, leg I, lateral (abaxial) view; B, leg II, dorsal view (setae d on femur – tibia not illustrated in place, but having the form of the figure at right); C, leg III, dorsal view; D, leg IV, dorso-lateral (abaxial) view.

FIGURE 4. Phyllochthonius ovatosetosus n. sp., immatures. A – B, larva, dorsal and ventral views, respectively; C – E, anogenital region of protonymph, deutonymph, and tritonymph, respectively.