Caddo dentipalpus

Caddo dentipalpus (C. L. Koch & Berendt, 1854)

Figs 1–6

Material examined. UKRAINE: SIZK K-2369 (jointly with SIZK K-2363–2368), SIZK K-27632 and SIZK K- 2880. All from Rovno amber, Rovno Oblast (Region), Sarny District, Klesov, Pugach quarry; late Eocene. Syninclusions: SIZK K-27632, stellate hairs/trichomes, Acari; SIZK K-2363, female of Chironomidae (Orthocladiinae); SIZK K-2364, two Collembola, Entomobryomorpha; SIZK K-2365, female of Chironomidae (Orthocladiinae); SIZK K-2366, Oribatida: Platyliodes ensigerus Sellnick; SIZK K-2367, two Collembola, Entomobryomorpha; SIZK K-2368, two Collembola, Entomobryomorpha.

Description. Within the darker resin, the body of SIZK K-2369 (Fig. 1) is deformed and covered dorso-laterally with an air bubble. During processing of the amber, the body of the harvestman (L: 0.825) was sawn off ventro-laterally. This fossil is female, as shown by the presence of three large thorns (acute tubercles/megaspines) ventrally on the femur of the pedipalp. Femur distally with a large mesal setose lobe/apophysis. All pedipalpal segments armed with stout setae, mostly on mesal surfaces. Claw large: 0.084. We could measure correctly only the length of palpal segments (Fe: 0.7, Pa: 0.32–0.35, Ti: 0.28–0.3, Ta: 0.56), and the length of some of the leg femurs (Fe I: 1.08, Fe II: 0.77).

SIZK K-27632 (Fig. 2) has a body dorsally obscured by the presence of breaks/cracks in the amber just above it. This specimen (L: 1.25) is also a female. A protruding ovipositor (furcal length: 0.126–0.14) (Fig. 2: arrow) is visible, as well as the presence of the three typical femoral megaspines. Ocular tubercle: length: 0.5, width: 1.0; diameter of each lens 0.175. Appendage lengths: chelicera, basal segment equivocal, distal segment 0.52, movable digit 0.17. We could correctly measure only the length of the following palpal segments: Cx: 0.3, Tr: 0.2, Ti: 0.22; Ta: 0.475; length of the tarsal claw: 0.07. Legs femur length: Fe II: 1.12, Fe III: 0.63; other femurs could not be measured accurately.

SIZK K-2880 (Figs 3–6) is not easily visible dorsally due to the presence of an air-pocket, as well as many cracks in the amber (Fig. 3). Ventrally, the body is covered with a white emulsion, as well as with filamentous fungal hyphae (Figs 4–5). It is noteworthy that a similar arthropod-pathogenic fungal overgrowth is usually observed on dead harvestmen in very humid conditions (Cokendolpher & Mitov 2007: 348–349, fig. 9.2; Wijnhoven 2009: 13–14, fig. 25; Barbosa et al. 2016: 13, fig. 2A–B; P. Mitov, pers. obs.). Three large thorns (acute tubercles) (Fig. 6) are clearly visible on the femur of the pedipalp, indicating that this specimen is again female (see Gruber 1974; Shear 1975). Its body has L: 1.37. The ocular tubercle (Fig. 3) is characteristic of the species—compared to the length of the body it is large, with length: 0.56, and width: 0.87, and diameter of each lens 0.238. The length of only a part of the palpal segments could be measured accurately: Fe: 0.35, Pa: 0.35, Ti: 0.28, Ta: 0.35; Legs femur length: Fe I: 0.76, Fe II: 1.12, Fe III: 0.74, Fe IV: 0.91.

Remarks. Caddo dentipalpus is easy to recognise among the European amber harvestmen through its combination of a very large and broad eye tubercle, very large eyes and large thorns (acute tubercles/megspines) on the palpal femur. It has also been recorded from Baltic and Bitterfeld amber (Table 1) and as discussed by Shear (1975) and Dunlop & Mitov (2009) it is of particular interest for being almost identical to a living species, Caddo agilis Banks, restricted today to North America and East Asia (Suzuki 1976). No species of Caddo, or even the family Caddidae, occur in the Recent European fauna and the Rovno records further indicate that Caddo was originally more widely distributed across Eastern Europe as well. Its modern relatives (Caddo agilis, C. pepperella Shear) are usually found in very humid, densely shaded areas, such as ravines, and there is usually a coniferous element in the forest (Shear 1975), or it can be found in bamboo thickets and beech forests (Suzuki 1976). Caddo agilis tends to occupy exposed surfaces (e.g., tree trunks, logs, stones) and C. pepperella occurs on the ground in the leaf litter and under fallen objects (Suzuki 1976; Shultz & Regier 2009). Caddo dentipalpus is found quite often in the European ambers. Perhaps the fossil species also preferred tree trunks, where it would have easily come into contact with sticky resin.