Amilenus deltshevi, Dunlop & Mitov, 2009

Dunlop, Jason & Mitov, Plamen, 2009, Fossil harvestmen (Arachnida, Opiliones) from Bitterfeld amber, ZooKeys 16, pp. 347-375 : 364-366

Amilenus deltshevi sp. n.

urn:lsid:zoobank.org:act:FE124EB4-D388-4C05-B1F4-B648AC935329

Figs 20-21 , 23-26

Holotype. MB. A 1659 . Bitterfeld amber, probably from the site of the Goitsche opencast Mine near Bitterfeld, Sachsen-Anhalt, Germany; Palaeogene (Oligocene: Chattian).

Additional material. MB.A. 1660 (paratype). From the same locality as the holotype.

Diagnosis. Fossil Amilenus species with a distinct form of the apophysis on the pedipalpal patella.

Etymology. In honour of Prof. Christo Deltshev (Sofia) in recognition of his extensive contributions to arachnology and on the occasion of his 70 th birthday.

Description. The holotype (MB.A. 1659, Figs 20 , 23-24 ) is an almost complete specimen in lateral view. Body ovoid, length ca. 0.8 mm; details of body, ocular tubercle and mouthparts equivocal. Pedipalps well-preserved, with article lengths (in mm) of: femur, 0.21; patella, 0.14; tibia, 0.16; tarsus, 0.4. Patella with a distinct, bluntly- pointed, mesal apophysis bearing a number of stout spines. Tibia slightly inflated distally and also bearing stout mesal spines in this distal region. Tarsus slightly expanded distally; apotele present as a short, curving, distal claw. Legs relatively complete; all elongate and slender, and when preserved at their full length ending in a single, claw like apotele. Leg 1 with article lengths in (mm) of: femur, 0.56; patella, 0.19, tibia, 0.47; metatarsus and tarsus (boundary indistinct) 1.75. Leg 2 with article lengths in (mm) of: femur, 1.19; patella, 0.22; tibia 1.72, metatarsus and tarsus (boundary indistinct) at least 1.47, but full length not preserved. Leg 3 less completely known, patella 1.1 mm; tibia 0.58 mm. Leg 4 with article length in mm of: femur c. 0.8; patella, 0.19; tibia, 0.75, metatarsus and tarsus (boundary indistinct), 3.0.

The paratype MB.A. 1660 ( Figs 21 , 25-26 ) is an almost complete specimen best seen in dorsal view, but missing the second pair of legs and the dorsal surface of the opisthosoma. Body oval to rectangular, length c. 1 mm; width of prosoma 0.7; width of opisthosoma 0.75. Ocularium present on the propeltidium, fairly large in proportion to the rest of the body; possibly hinting at a juvenile. Length 0.174 mm, width 0.215 mm, distance from ocular tubercle to the front of prosoma 0.110 mm. Meso- and metapeltidium, together with the tergal region of the opisthosoma equivocal. Pedipalps quite well-preserved. Both patella and to a lesser extent tibia express mesal apophyses, with fairly dense setation along the entire mesal surface of these articles. Leg 1 with article lengths (in mm) of: femur, 0.95; patella, 0.23; tibia, 1.02; metatarsus, 0.79; tarsus, 1.44. Some annulation of the tarsus preserved, but details lacking. Leg 2 only known from an incomplete femur on the left side. Leg 3 with article lengths (in mm) of: femur, 0.78; patella, 0.20; tibia, 1.02; metatarsal-tarsal division, indistinct but length together 2.8. Annulation of the tarsus into at least 12 elements and the distal apotele in the form of a single curving claw also visible in this limb. Leg 4 with article lengths (in mm) of: femur, 0.1.42; patella, 0.21; tibia, 1.28; metatarsal-tarsal division, indistinct but length together at least 1.8.

Remarks. The key character in both these specimens is the mesal apophysis on the patella of the pedipalp ( Figs 24, 26 , arrowed). Not as long as the apophysis of Dicranopalpus (see above), it closely matches the gross morphology of extant species such as Amilenus aurantiacus ( Simon, 1881) ( Fig. 22 , arrowed) where even juveniles – the fossils could also be subadult – express such an apophysis. Based on this we recognise these Bitterfeld fossils as a new species, and the first fossil example of Amilenus . Howev- er, some expected details compared to extant members of this genus, like pseudoannulation of tibiae 2 and 4 or teeth on the pedipalp claw, could not be resolved; although the latter may not be present in modern juveniles of this size (i.e. body length). In the holotype the ocular tubercle is probably hidden behind the legs and is rather small in extant species. Also of note is the fact that the tibia of leg 2 in modern juveniles is longer than femur; a situation paralleled by the holotype.

One of our initial suspicions was that this new material could be conspecific with the Baltic amber species Opilio ovalis Koch & Berendt, 1854 . Its holotype could not be traced in its expected repository in Berlin (cf. Dunlop 2006), but the original illustration implies the presence of a somewhat distally thickened and mesally rather setose

pedipalp patella. However, the Bitterfeld material differs from the O. ovalis illustration in having a distinct, projecting apophysis on the patella and strong setae on the tibia too. We are fairly certain that O. ovalis is misplaced at the genus level, but since the focus of the present paper is the Bitterfeld deposit, we will address this question fully in future work on Baltic amber harvestmen.

Figures

Figure 20-22. Fossil and Recent Amilenus. 20 Amilenus deltshevi sp. n., M.BA 1659 (holotype), from Bitterfeld amber (Palaeogene: Oligocene) 21 A. deltshevi sp. n. M.BA 1660 (paratype), also from Bitterfeld amber 22 Juvenile Amilenus aurantiacus (Simon, 1881) (Recent harvestman for comparison), note the medial apophysis on the patella (arrowed). Scale bars equal 1.0 mm.

Figures 23-26. Amilenus deltshevi sp. n. Camera lucida drawings of the specimens shown in 20-21. 23 MB.A 1659 (holotype), from Bitterfeld amber (Eocene: Oligocene) 24 the same, detail of the pedipalp showing the patellar apophysis (arrowed) 25 MB.A 1660 (paratype) 26 the same, detail of the anterior prosoma and pedipalps showing the patella apophysis (arrowed). Scale bars equal 1.0 mm (23, 25), 0.2 mm (24, 26).