Conservation of imperiled crayfish -: Orconectes (Procericambarus) peruncus (creaser, 1931) (decapoda: cambaridae)

Conservation Status.-Threatened (Taylor et a]., 1996). Imperiled in Missouri and globally (S2, G2; Missouri Natural Heritage Program, 2006). Based on the species' limited distribution (< 20,000 km(2)) and its observed decline in significant reaches of several streams reported here, O. peruncus (Creaser, 1931) has been classified as Vulnerable, VU B 1b(i, iv), following IUCN (200 1). Identification.-The Big Creek crayfish (Fig. 1), Orconectes peruncus, was first described by Creaser (1931) as Cambarus peruncus from Little Creek, a tributary to Big Creek in the St. Francis River drainage, near the town of Chloride, Iron County, Missouri (Fig. 2). This species is a member of the subgenus Procericambarus as defined by Fitzpatrick (1987). The form I male gonopods are long with slender, tapering central projections slightly curved posteriorly and reaching to the bases of the first pereiopods when the pleon is flexed (Creaser, 1931; Pflieger, 1996). The mesial projection of the gonopod is distinctly shorter and thicker than the central projection, and is grooved along its anterior margin, and the apex is widened and recurved (Creaser, 193 1; Pflieger, 1996). Form I males possess hooks on the ischia of the third and fourth pereiopods that are reduced in size in form 11 males. The female's annulus ventralis possesses an elevated extension on its posterior margin, an irregularly curved sinus, and a wide, shallow fossa (Creaser, 1931; Pflieger, 1996). The crayfish's base color is described as olive green to tan or brown with many dark spots on the chelae, cephalothorax and pleon, and a prominent blackish saddle stretching laterally across the dorsal surface of the posterior edge of the cephalothorax and anterior edge of the pleon.