Phalangiidae, Latreille, 1802

BARTEL, CHRISTIAN & DUNLOP, JASON A., 2023, First eupnoid harvestmen (Arachnida: Opiliones: Eupnoi) from mid-Cretaceous Kachin amber, with notes on sexual dimorphism in Halitherses grimaldii (Arachnida: Opiliones: Dyspnoi), Palaeoentomology 6 (3), pp. 278-291 : 283

Phalangiidae indet. 1

( Fig. 4 )

Material. coll. Patrick Müller, BUB4516.

Locality and horizon. Burmese amber, Hukawng Valley, Kachin State, Myanmar; mid-Cretaceous.

Description. Body relatively small, oval and somewhat granulated, L 1.12, anterior W 0.58, maximum posterior W 0.66. Ocularium very small, slightly elevated and oval with two lateral eye lenses, L 0.15, W 0.10. Eye lens diameter 0.04. Chelicerae rather large. Cheliceral distal segment with a few small spines. Cheliceral basal segment L 0.19; distal segment L?, with fixed and movable finger. Pedipalps sparsely covered with setae. Pedipalp tarsus elongated bearing a single claw at its tip. Pedipalp length: fe 0.20, pa 0.14, ti 0.15, ta 0.31, total (fe–ta) 0.80. Legs extremely long (leg II and IV longest) and covered with a few setae. Tarsus I–IV bear a single smooth claw. Tarsal formula: 9–10:32:12–14:14–15. Leg length: Leg I cx 0.22, tr 0.10, fe 0.54, pa 0.17, ti 0.61, mt 0.51, ta 1.10, total (cx–ta) 3.25; Leg II cx 0.54, tr 0.12, fe 1.44, pa 0.24, ti 1.56, mt 0.88, ta 3.24, total (cx–ta) 8.02; Leg III cx 0.40, tr 0.10, fe 0.63, pa 0.12, ti 0.63, mt 0.56, ta 1.46, total (cx–ta) 3.90; Leg IV cx 0.45, tr 0.10, fe 0.83, pa 0.24, ti 0.76, mt 0.80, ta 2.05, total (cx–ta) 5.23.

Remarks. BUB4516 ( Fig. 4A–C ) could be a juvenile/subadult, due to its relatively small body size and the straight pedipalp tarsus. The number of tarsomeres on leg II, which potentially exceeds 30, suggests a later developmental stage. The presence of a pedipalp claw and single claws on all legs again support referral to Eupnoi . Despite the uncertainty of the developmental stage most of the modern Eupnoi families can be excluded. Members of the family Caddidae are typically characterized by the presence of a huge, well developed ocularium with large lateral eyes, whereas the fossil has only a small, slightly raised ocularium ( Fig. 4A, B ). A smooth pedipalp claw further tends to rule out the family Sclerosomatidae , which usually have a pectinate pedipalp claw ( Martens, 1978). The absence of a scutum parvum and a heavily sclerotized dorsal body, which are also typical characters for sclerosomatids, additionally supports their exclusion. The Australasian family Monoscutidae and its two subfamilies Megalopsalidinae and Monoscutinae can also be excluded as the fossil lacks the enlarged chelicerae or the shortened legs (femur I is often shorter than the body width) respectively ( Fig. 4 ). Additionally, the fossil shows neither an elongate pedipalp patella, nor the rather short and thick legs and reduced pedipalp claw often found in the family Neopilionidae . This leaves the families Protolophidae and Phalangiidae . Protolophidae are characterized by a pedipalp tarsus which is shorter than the pedipalp tibia ( Fig. 4C ) combined with relatively short legs. Females also have slender pedipalps with an apophysis on the pedipalp patella or tibia. Males on the other hand have greatly thickened pedipalps. All of these characters are absent in the fossil. As most of the important characters are consistent with members of the family Phalangiidae , the fossil is tentatively placed therein. The lack of significant morphological characters makes a placement at genus level very difficult. Its closest living relatives can probably be found in the genera Phalangium Linnaeus, 1758 , Metaphalangium Roewer, 1911 , Opilio Herbst, 1798 or in one of the Asian genera described by e. g., Martens (1973). In lieu of an adult specimen, the fossil is placed for now as Phalangiidae indet. but described and figured here for completeness.

Figures

FIGURE 4. BUB4516 Phalangiidae indet. 1. A, Dorsal overview (camera lucida drawing). B, Close-up of the body in dorsal view. C, Close-up of the body in ventral view. Abbreviations: ch, chelicerae; cx, coxa; fe, femur; mt, metatarsus; oc, ocularium; pa, patella; pp, pedipalp; ta, tarsus; ti, tibia; legs numbered from I–IV. Scale bars = 1.0 mm (A) and 0.5 mm (B, C).