Balticoroma wheateri Penney & Marusik

Penney, David, Mcneil, Andrew, Green, David I., Bradley, Robert, Marusik, Yuri M., Withers, Philip J. & Preziosi, Richard F., 2011, A new species of anapid spider (Araneae: Araneoidea, Anapidae) in Eocene Baltic amber, imaged using phase contrast X-ray computed micro-tomography, Zootaxa 2742, pp. 60-66 : 61-62

Balticoroma wheateri Penney & Marusik new species

Figs 1–21

Type material. Holotype male: in Eocene Baltic amber from Lithuania ( GPIH 4666).

Etymology. Named after Professor C. Philip Wheater, co-author, colleague and friend of the senior author.

Diagnosis. The new fossil species is easily distinguished from all other anapid spiders by the male having clypeal extensions that run parallel to the ectal surface of the chelicerae ( Figs 8, 15 ) and in having the metatarsus of the first leg reduced and modified into what is presumably a y-shaped clasping structure ( Figs 10–14 ). The female is unknown.

Description. Male holotype. Total length 1.8 mm. Carapace with a distinctly elevated pars cephalica clearly demarcated from the pars thoracica by a procurved groove ( Figs 2, 4 ). The eyes are not visible under light microscopy, but based on CT scans there appear to be eight eyes reasonably closely-grouped, with each pair more or less contiguous; posterior median eyes largest, anterior median eyes smallest. An unusual 'sulcus' runs dorso-ventrally on the right lateral surface of the pars thoracica ( Figs 2, 4 ), but this is absent on the left side of the specimen so is an artefact of preservation. The clypeus is very high, at least five times the diameter of the AME, with unusual, ventrally-projecting extensions running along the ectal surface of each cheliceral paturon ( Figs 6 , 8, 15 ). These have been confirmed as extensions of the carapace rather than the chelicerae, as each is clearly segmented from the latter and fully attached to the carapace in the raw data slices ( Figs 15, 16 ). The chelicerae are relatively long and narrow, with a short fang. Sternum subcircular, maxillae and labium wider than long. A labral spur is present between each cheliceral paturon ( Fig. 8 ).

Leg formula 1243, lacking distinct macrosetae, but with a short bristle distally on each patella and two short bristles dorsally on each tibia; tibia 3 with only one short dorsal bristle ( Fig. 1 ). Each tarsus with three claws, lacking accessory setae; tarsi longer than metatarsi. Leg 1 heavily modified, with all segments apart from the tarsus distinctly swollen; metatarsus 1 forked distally forming what is presumably a y-shaped clasping structure ( Figs 2, 3, 6 , 10–14 ). Pedipalpal structure not clearly visible using computed tomography, however, the femur and tibia lack apophyses and the patella has a small number of stiff setae at the tip; cymbium with a dorsal outgrowth ( Fig. 17 ) (= the “paracymbium” sensu Wunderlich's diagnosis). There is a long sinuous embolus originating proximally, forming a coil and projecting ectally ( Figs 9, 17–21 ), associated with what appears to be a bent functional conductor ( Figs 19–20 ) sensu Wunderlich (2004). Abdomen orientated almost at a right angle to the longitudinal axis of the body; dorsal surface covered with a single, smooth scutum and short setae. Ventral side of abdomen with a smaller epigastric scutum and lateral folds; spinnerets short, unmodified and surrounded by a sclerotized ring.

Female: unknown.

Distribution. Extinct. Known only from Eocene Baltic amber.

Figures

FIGURE 1. Microphotograph of Balticoroma wheateri new species (male holotype, GPIH). Body length = 1.8 mm.

FIGURES 2 – 7. CT reconstructions of Balticoroma wheateri new species (male holotype, GPIH). (2) right lateral view; (3) left lateral view; (4) dorsal view; (5) ventral view; (6) anterior view; (7) posterior view. Body length = 1.8 mm. Mt 1, metatarsus 1; ta 1, tarsus 1; ti 1, tibia 1.

FIGURES 8 – 21. CT reconstructions of Balticoroma wheateri new species (male holotype, GPIH). (8) frontal view showing chelicerae and labral spur; (9) view of right pedipalp showing embolus; (10 – 14) various views of right metatarsus 1, showing y-shaped clasping structure; (15) anterior view of specimen showing the section taken through the chelicerae to produce the raw data slice in Figure 16; (16) raw data slice demonstrating that the chelicerae and clypeal extentions are clearly separated; (20 – 21) various views of the right pedipalp. C, chelicera; ce, clypeal extension; co, dorsal cymbial outgrowth; cy, cymbium; e, embolus; eb, embolic base; ec, embolic coil;? fc, functional conductor sensu Wunderlich (2004); ls, labral spur; t, tegulum.