Metaphalangium martensi, Mitov & Perkovsky & Dunlop, 2021

Mitov, Plamen G., Perkovsky, Evgeny E. & Dunlop, Jason A., 2021, Harvestmen (Arachnida: Opiliones) in Eocene Rovno amber (Ukraine), Zootaxa 4984 (1), pp. 43-72 : 53-57

Metaphalangium martensi sp. n.

Figs 9–11 , 13–14

Type material. UKRAINE: Holotype. SIZK K-3197, Rovno region, Sarny District, Klesov, Pugach quarry; late Eocene. Syninclusions: SIZK K-3197, stellate hairs/trichomes; Diptera : Rhagionidae . Paratype: SIZK K-1254, with same data as for holotype, but syninclusions absent. Both from Rovno amber.

Etymology. In honour of Prof. Jochen Martens (Mainz, Germany) in recognition of his extensive contributions to arachnology/opilionology, and on the occasion of his 80th birthday; name in the genitive case.

Diagnosis. Easily distinguished from all other fossil phalangiid species by the unique combination of: (1) palpal patella with a small and blunt medio-distal prominence, (2) palpal patella and tibia mesially covered with not densely spaced stout spine-like setae, typically arranged brush-like in 4–5 rows, (3) absence of a distal apophysis on the palpal tibia, (4) the ocular tubercle (ellipsoidal, normal in size) is up to twice its length from the frontal margin of the carapace, and (5) having thin and relatively long legs.

Description. The holotype, SIZK K-3197, is an almost complete specimen ( Figs 9–10 ), possibly hinting at a juvenile/immature, best seen in dorsal view, but missing the ventral surface of the body (together with the leg coxae, and parts of the pedipalpal coxae and femora). Body, partly dorsally hidden in a gas bubble, and by a white emulsion anterior to the ocular tubercle. Body ovoid, light colored (colouration in amber – pale gray-yellow) with a silverish shine; length ca. 1.75; width of prosoma 1.5; width of opisthosoma 1.65. Ocular tubercle broader than long: length 0.175, and width 0.30, with 2–3 tubercles on the eye rings; diameter of each lens 0.15. Distance from ocular tubercle to front of prosoma 0.325. Ocular tubercle up to two times of its length from the frontal margin of the carapace.

Pedipalps (with sawn-off coxae and femurs; the latter have only their distal parts preserved, with a length of 0.25), with article lengths of: Pa: 0.2; Ti: 0.32; Ta: 0.65; the claw, 0.07. On the preserved distal parts of the femurs there are spine-like setae apically and ventrally, ordered roughly in two rows. Palpal patella with a small and blunt medio-distal prominence; palpal patella and tibia mesially covered with not densely spaced stout spine-like setae, specifically brush-like, ordered in 4–5 rows ( Fig. 11 : arrows). These spine-like setae are 0.05–0.07 high and the distance between them is 0.03–0.04. On the medial surface of the patella they number 16–18, while on the medial side of the tibia they are about 26–28. Similar spine-like setae are scattered on the surface of the palpal tarsus as well, along with thinner setae; tarsus ends in a claw ( Fig. 11 ).

Legs relatively complete ( Figs 9–10 ), all elongate and slender, and when preserved at their full length ending in a single claw. Leg article length: Leg I (Fe: 1.85, Pa: 0.5, Ti: 1.6, Mt: 1.75, Ta: 2.85–3.0); Leg II (Fe: 3.7, Pa: 0.5–0.6, Ti: 3.5, Mt: 3.25, Ta: 7.75); Leg III (Fe: 1.9, Pa: 0.35; full length of tibia, metatarsus, and tarsus not preserved [i.e., sawn-off]); Leg IV (Fe: 2.75, Pa: 0.55, Ti: 2.0, Mt: 2.85; full length of tarsus not preserved [partially sawn-off]). Index of leg length (IL) = 1.23.

The leg segments are cylindrical; femurs with longitudinal rows of acute inclined tubercles; thinnest are the femurs of the second pair of legs, thickest those of the first and third pairs. Their patellae bear dorsally and ventrally sparse setae and dorso-distally two tubercles each. Tibia distally slightly dorso-ventrally flattened, with sparse setae laterally and with more setae on the ventral side. Metatarsus with few setae on all sides. Tarsi with short, fine and numerous setae on their ventral sides.

The paratype, SIZK K-1254, is enclosed in very dark amber ( Fig. 13 ). During processing of the amber piece, the ventral body surface was sawn off with parts of the legs. Body length 1.62; prosoma width 1.25, abdomen width 1.25, possibly also hinting at a juvenile/immature. The body dorsally, the ocular tubercle, the chelicerae, the pedipalps and parts of the legs are covered with a white emulsion. Therefore, only part of the pedipalpal and leg segments can be seen and measured. Pedipalps ( Fig. 14 ), with article lengths of: Fe: 0.35–0.4, Pa: 0.21, Ti: 0.37, Ta: 0.62. Palpal femurs dorso-apically and ventrally with stout spine-like setae, palpal patella and tibia medially also with stout spine-like setae. Palpal patella and tibia dorsally with setae; palpal tarsus with many setae; tarsus ends with a claw. Palps covered with a white emulsion, thus features of the setae appear much thicker than they would have been in life – compare with the holotype ( Fig. 11 ). Leg article length: Leg I (Fe: ca. 1.5, Pa: 0.37, Ti: 1.25, Mt: 1.75, Ta: 1.125); Leg II (Fe: 2.75, Pa: 0.37); Leg III (Fe: 1.3, Pa: 0.36); Leg IV: femur is sawn off, the rest of it 2.0 mm long. Index of leg length (IL) = 1.2. The remaining leg segments are sawn off or cannot be measured correctly.

Remarks. The key characters of this new fossil Metaphalangium species are the small mesal projection on the palpal patella, in combination with the characteristically arranged stout spine-like setae along the entire mesal surface of palpal patella and tibia ( Figs 11 , 14 ). However, these stout spine-like setae (in the holotype at least; Fig. 11 ) are much thicker than those in extant forms; see the juvenile Metaphalangium cirtanum ( Fig. 12 ).

When apophyses are present in phalangiid harvestmen, they can be more prominent in immature instars and become less well expressed in adults ( Mitov et al. 2015: p. 41; PGM, pers. obs.) and representatives of Metaphalangium are no exception. In extant members of this genus only the adults (both sexes) of Metaphalangium corsicum (Roewer) and Metaphalangium lusitanicum (Roewer) have short palpal apophyses. Of the studied representatives of the genus (see Material and methods), in adults of M. cirtanum (females) and M. strandi (both sexes), only the palpal patella bears a mesially pronounced rounded protrusion at the distal end, while in juvenile M. cirtanum the pedipalpal patellae bear clearly formed apophyses ( Fig. 12 ). Conversely, in immature specimens of Metaphalangium martensi sp. n. such apophyses are missing—the palpal patella bears only a small and blunt medio-distal prominence ( Fig. 11 : black arrow). Differences can also be seen in the morphology of the legs: in both immature fossil specimens they are somewhat more slender than in extant juvenile Metaphalangium , and the index of leg length (IL) in the smallest studied juvenile M. cirtanum (with L: 3.3) is 1.06., while in M. martensi sp. n. (with L: 1.62–1.75), IL varies between 1.2 and 1.23.

Figures

FIGURES 9–10. Metaphalangium martensi sp. n., holotype, SIZK K-3197, from Rovno amber (Klesov, Pugach quarry, Ukraine), late Eocene (ca. 36–37 Ma). 9 Dorso-lateral overview of the complete animal. 10 Detail of body in dorso-lateral view. Scale bars: 2 mm.

FIGURES 11–12. Metaphalangium spp., detail of the anterior prosoma and pedipalps. 11 Metaphalangium martensi sp. n. (holotype, SIZK K-3197, from Rovno amber, Klesov, Pugach quarry, Ukraine; late Eocene). Note the palpal patella with small and blunt medio-distal prominence (black arrow) with stout spine-like setae and mesial brush of stout spine-like setae on palpal tibia (white arrow), ventral view. 12 Comparative image of the extant species Metaphalangium cirtanum (C. L. Koch) (juvenile from Albania: Zvërnec), white arrows indicate palpal patella and tibia, mesially covered with stout spine-like setae, dorso-lateral view. Scale bars: 0.3 mm.

FIGURES 13–14. Metaphalangium martensi sp. n., paratype, SIZK K-1254, from Rovno amber (Klesov, Pugach quarry, Ukraine), late Eocene. 13 Lateral overview of the complete animal (white arrow points the pedipalps). 14 Detail of pedipalps, lateral. Scale bars: 13: 1 mm; 14: 0.5 mm.