Eupnoi

Gainett, Guilherme, Sharma, Prashant P, Fernandes, Nathália, Pinto-Da-Rocha, Ricardo, Giribet, Gonzalo & Willemart, Rodrigo Hirata, 2019, Evolution of a sensory cluster on the legs of Opiliones (Arachnida) informs multi-level phylogenetic relationships, Zoological Journal of the Linnean Society 187 (1), pp. 143-165 : 150

Eupnoi

Tarsi I and II of Eupnoi species also have three sensilla with short conic shafts and flat articulation membranes in the same corresponding position as Laniatores , which we refer to as sensilla basiconica.These structures differ from the ones in Laniatores in their disposition and morphology of the shaft opening. In the unidentified phalangiid species ( Eupnoi , Phalangiidae ), both legs I and II have a triad of sensilla basiconica in the distal third of the tarsomere ( Fig. 9A–D ). In its proximal third, the dorsal surface of the last tarsomere also has two and four additional isolated sensilla basiconica on legs I and II, respectively ( Fig. 9A ). In Astrobunus grallator ( Sclerosomatidae ), a similar triad of sensilla basiconica occurs in the distal third of legs I, but legs II have only isolated sensilla basiconica in a dorsal position, totalling seven. Legs I also have two isolated sensilla basiconica ( Fig. 10A, B ) in the proximal third of the tarsomere and thus the total number in the tarsomere is five sensilla. The apical portion of the sensilla basiconica of the unidentified phalangiid has a pore-like structure ( Fig. 9B–D ), while in A. grallator there is a pore opening with a slit below it ( Fig. 10C ). This second condition is similar to the morphology observed in Anelasmocephalus sp. ( Dyspnoi , Fig. 8C ). Even though the three shafts in the triad are similar in shape, the three shafts are progressively longer in the unidentified species ( Phalangiidae ), with the most distal being the longest and thickest ( Fig. 9C, D ). In A. grallator the three shafts have a similar length ( Fig. 10C ).

Figures

Figure 8. Dyspnoi. Anelasmocephalus sp., undetermined sex.A, dorsal region of the distal third of the distalmost tarsomere II, showing the three sensilla with flat articulation membranes (see text for explanation), lateral view. B, proximal sensillum (3) of the three marked in ‘A’, lateral view. C, middle sensillum (2) on the same region of leg I, frontal-superior view. D, detail of the tip of the distal sensillum (1) in ‘A’, lateral view. Ps: pore-like structure; white arrowhead: slit opening; 1: hooded sensillum; 2: middle sensillum basiconicum; 3: proximal sensillum basiconicum.

Figure 9. Eupnoi. Unidentified species (Phalangiidae), female. A, frontal view of the last tarsomere I. B, detail of an isolated sensillum basiconicum proximal to the triad. C, detail of the triad (1–3) on the distal third of the tarsomere I shown in ‘A’. Note the all thee sensilla share the same articulation membrane. D, detail of the same region on leg II, showing the triad (1–3). Note that the three sensilla have increasing length of the shaft, from proximal to distal (3 to 1). Black arrow: proximal sensilla basiconica; white arrowhead: apical opening; 1: hooded sensillum; 2: middle sensillum basiconicum; 3: proximal sensillum basiconicum.

Figure 10. Eupnoi. Astrobunus grallator (Sclerosomatidae), undetermined sex. A, lateral view of the last tarsomere I, indicating three sensilla (1–3) clustered on the distal-third region, and two isolated sensilla basiconica on the middle of the tarsomere. B, detail of an isolated sensillum basiconicum on the last tarsomere I, dorsal region. C, detail of the three sensilla clustered on ‘A’. Black arrow: proximal sensilla basiconica; Cw: claw; white arrowhead: apical opening; 1: hooded sensillum; 2: middle sensillum basiconicum; 3: proximal sensillum basiconicum.