Labidostomma paleoluteum, Dunlop & Bertrand, 2011

Dunlop, J. A. & Bertrand, M., 2011, Fossil Labidostomatid Mites (Prostigmata: Labidostommatidae) From Baltic Amber, Acarologia 51 (2), pp. 191-198 : 193-195

Labidostomma paleoluteum sp. nov.

( Figures 1–4 )

Etymology

From the Greek palaios (Παλαιοc) ’old’ and the suffix luteum derived from a similar-looking, and perhaps closely related, Recent species Labidostomma luteum Kramer, 1879 .

Material

F21521/ BB / AC /CJW. Two specimens (here designated as a holo- and paratype) within a single piece of amber ( Fig. 1 ); together with a staphylinid beetle, one eupodoid mite and some collembolans as syninclusions. Baltic amber, precise locality not recorded; Palaeogene (Eocene) .

Description

Notation follows F. Grandjean (1942). Dorsal view only visible in both specimens; body cuticle distinctly sclerotized, with alveolate ornamentation, clearly visible anteriorly, in central zone and in lateral fields on the opisthosoma ( Figs 2–3 ). Anteriorly the body is rounded with a terminal eye clearly visible in a frontal position. Dorsal setation is distinguished and visible via the setae themselves or by the insertion points of missing setae: two pairs of trichobothria (boa and bop), rather long, each with at least two or three branches. Aspidosomal setae: ga (long), ge, gm, gr as in L. luteum . Laterally the glandlike organ (pustule) is visible at least on the left side near the seta gr which is long. Perturbation in ornamentation near the base of gr interpreted here as the lateral eye. Opisthosomal setae: usual files of simple setae, lateral and dorsal da to de and la to le.

A lateral cuticular accident on the posterior end of the dorsal shield could be a supplementary pustule (similar to L. jacquemarti Coineau, 1964 or vialeae Bertrand, 1981), in a postero-lateral position

Dunlop J. A. and Bertrand M.

on the dorsal shield. However, it could be an artefact; several Recent species express changes in cuticular cells in this same zone. Cuticle: when wellvisible reticulate with polygons. Ornamentation poorly visible on remainder of the dorsal shield which could be punctate or granulate. In recent labidostommids the cuticular polygons often vanish into granular, or increasingly less visible foveate, ornamentation from the peripheral to central dorsal shield.

Gnathosoma — Only visible in dorsal view. Fixed digit: extremity as in L. luteum or integrum dorsal subterminal setae chb was not visible. Setae cha long, proximally inserted on a tubercle (base hidden by dorsal shield). Palp visible from tibia to tarsus: habitual form, some unbroken setae present, especially the terminal seta that forms the terminal eupathidia characteristic of the family; a small lateral seta could represent the tarsal solenidion. Rest of setation compatible with usual pattern (1, 1, 3, 4+ ω).

Legs — The legs show habitual division into tripartite femora, and on the first pair articular function is devoted to telofemur-genu junction rather than to genu-tibia junction, as in the Recent species. PII-PIV claws not visible. PI: claw with two ungues, with long tarsal setae (simple setea). Terminal lateral setae long corresponding to the tarsal eupathidiae described from extant labidostommids. Chaetotaxy: Tibia: the usual setae are found; i.e. the long dorsal or ventral setae (terminal and median) and dosolateral and ventrolateral files. Tarsus poorly visible, but dorsally three hard to interpret anomalies could represent two dorsal tarsal solenidia, and the famulus that could be luteum -like; a barely visible rounded mass seems to be lightly discernible but would need more precise examination to confirm its identity.

Acarologia 51(2): 191–198 (2011)

Dimensions (all in µm) — Total length 610. Dorsal shield = 550 long, 320 wide.

Frontal eye 30 diameter; gland-like organ: diameter 27 – 30, setae: trichobothria length 60 – 70, dorsal setae length about 50 – 60. PI: tarsus length 65 (without claws); tibia length 150 – 160; genual length about 120; Femur: length 125. Cheliceral proximal seta length 75. Terminal palpal seta length 40 – 50.

Diagnosis

Although examination is only possible in dorsal view, the general morphology of this species corresponds to the pattern of the genus Labidostomma . It could not be confused with cornuta Canestrini et Fanzago, 1877 neither with the group of species related to L. integrum which are characterized by subterminal anterior eye, or cuticular pattern, length of tibia, development of lateral gland-like organ. Among the described species L. (Nicoletiella) paleoluteum n. sp. resembles L. luteum or L. denticulata Schrank, 1781 and should be classified in the same subgenus. Close to luteum in terms of size, dorsal ornamentation and appendages ornamentation, it differs from it and denticulata by absence of the frontal projections (cornua) that characterize these species. Lengths of articles in the first pair of leg are very similar to L. luteum , which is the most widely distributed species in Europe occurring from Mediterranean climates to Finland.

Figures

FIGURE 1: Overview of the amber piece including the two labidostommatid mites (L1: holotype; L2: paratype), both described here as new; a eupodoid mite (E), a number of colembollans (C) and a staphylinid beetle (B). The association of the mites with one of their typical prey items (collembolans) is noteworthy. Scale bar equals 2 mm.

FIGURE 2: Labidostoma paleoluteum sp. nov. a – Holotype. b – Paratype. From Baltic amber (Palaeogene: Eocene). Both in dorsal view; scale bars equal 0.2 mm.

FIGURE 3: Interpretative camera lucida drawings of the specimens shown in Fig. 2. a – Holotype. b – Paratype. Both in dorsal view; scale bar equals 0.2 mm.

FIGURE 4: Morphological details. a-b – Dorsal view, specimen 1 and 2; c – P1 tibia and tarsus; d – P1;. e – Palp terminal articles. f – Detail of anterodorsal sculpture. Abbreviations: ζ eupathidium, ω tarsal solenidion, boa-bop: trichobothria, cha: proximal cheliceral seta, F: famulus, ga, ge, gm, gr: aspidosomal dorsal setae, k": tibial famulus, la to le and da to de: lateral and dorsal files of setae, P: posterolateral cuticular irregularity of dorsal shield. Tr, Bf, Mf, Tf, Ge; Ti, Ta: articles of PI (trochanter, basi, medio, telo femora, genu and tarsus)