Bioacoustics of Mermessus jona

Description. Male : from the Bath Nature Preserve, Summit Co., Ohio, USA : total length 1.08 mm ; carapace 0.48 mm long, 0.33 mm wide; carapace smooth, shiny, lacking pits and lobes, dull yellow with diffuse pattern of very light orange radiating from midline; anterior portion around eye region and clypeus slightly darker than remaining carapace; 3 erect setae along midline; sternum strongly concave and light yellow with sparse setae; endites with sparse setae on ventral surface, and blunt and lightly sclerotized along anterior margin. In lateral view, carapace level in anterior two-thirds, then gently sloping to pedicel in posterior third; carapace margin whitish along posterior half. Anterior eye row procurved, with eyes closely situated together; anterior median eyes small, just less than half the diameter of anterior lateral eyes. Anterior lateral eyes and posterior lateral eyes with reflective tapetum, while anterior median eyes and posterior median eyes apparently lack a tapetum. Posterior eye row slightly procurved; posterior median eyes large, oval, and separated by at least the diameter of anterior median eyes; anterior lateral eyes and posterior lateral eyes nearly touching. Clypeus with small, erect seta just below anterior median eyes. Chelicerae light orange with sparse setae, each with a single lightly sclerotized spur on antero-prolateral face in distal fourth of the chelicera, and with 5–8 stridulatory ridges; cheliceral promargin and retromargin each with five denticles. Abdomen unicolor, nearly white, with short sparse setae; colulus one quarter the length of anterior spinnerets; posterior lateral spinnerets and anterior lateral spinnerets conical, with posterior lateral spinnerets subequal in length to anterior lateral spinnerets. Legs dull yellow, slightly darkening distally; coxa IV with stridulatory pick situated distally on retrolateral side; TmI 0.45; TmIV absent; dorsal tibial macrosetae 2221. Femur and patella of palpus normal and light yellow with stridulatory pick at base of femur; tibia darker than patella; tibia ( Fig. 7 ), cup-shaped, with dorsal portion rising to a heavily sclerotized apophysis that terminates in two blunt teeth (prolateral view) subequal in length. In mesal view, tibia with a deep groove which runs from the separation between the two blunt teeth of the tibial apophysis to the base of the cymbium. Paracymbium large, quadrate, smooth, with distinct spur on dorsal margin, with blunt hook on ventral margin, and with proximal end bearing five setae ( Figs. 5, 6 ). Embolus lightly sclerotized, with its blackened tip protected by a translucent embolic membrane ( Fig. 8 ). Embolus situated distally on radix ( Fig. 8 ; the “embolic division” in Bishop & Crosby, 1938 ), radix with mesal tooth (“ventral projection” of Millidge, 1987 ), and with large hooked tailpiece (“median projection” of Millidge, 1987 ) ( Fig. 5, 8 ). Lateral to the hooked tailpiece is the heavily sclerotized, spoon-shaped distal suprategular apophysis ( Figs. 5, 6 ), which may easily be confused for a portion of radix. Female: from 18 km E of Gananoque, Ontario, Canada : total length 1.08 mm ; carapace 0.42 mm long, 0.35 mm wide. Description is as for the male with the following deviations: chelicerae lacking spurs; cheliceral Epigynum ( Fig. 10 ) weakly sclerotized, with copulatory openings situated side-by-side at base of epigynum and barely covered by the undivided ventral plate of epigynum; copulatory ducts well sclerotized and laterally arching away from copulatory openings towards the spermathecae ( Figs. 9, 10 ), terminating at the spermathecae in a short, lateral turn towards midline of the epigynum ( Fig. 10 ). Spermathecae broadly separated and situated anteriad to anterior margin of ventral plate ( Figs. 9, 10 ); fertilization ducts oriented mesally. Epigynal dorsal plate small and weakly developed ( Fig. 11 ). Variation. Males: Six males gave the following (mean ± 1 SD): total length 1.03 ± 0.10 mm ; carapace 0.52 ± 0.06 mm long, 0.39 ± 0.06 mm wide. Carapace dull yellow or whitish to light orange; sternum light yellow to whitish with sparse setae. Females: Three females gave the following (mean ± 1 SD): total length 1.05 ± 0.09 mm ; carapace 0.43 ± 0.05 mm long, 0.33 ± 0.05 mm wide. Natural history. Little is known of the natural history of this species. Other than the lost holotype specimen and a few specimens from Illinois, specimens of this species have been caught largely in pitfall traps, generally in open habitats such as grasslands, though the Illinois specimens were caught in a degraded oak savannah. Thus, M. jona is likely an epigeal spider of grassland and oak savannah habitats. Nearly all documented specimens are males, leading us to conclude that males are relatively mobile.