Polycentropus chelatus Ross and Yamamoto 1965

Polycentropus chelatus Ross and Yamamoto

(Figures 15–16, 42)

Polycentropus chelatus Ross and Yamamoto, 1965: 243, fig. 3, J; type locality ′Sugar Tree, Decatur Co., Tennessee, along Kentucky Lake, tributary of Morgan Creek ̍ (INHS). Polycentropus chelatus Armitage and Hamilton, 1990: figs. A–D, J.

Polycentropus chelatus Moulton and Stewart, 1996: figs. 558–559, J.

Diagnosis. Males of P. chelatus are distinguished from all other males of the P. confusus species group other than P. neiswanderi by the thumb-like, digitiform basodorsal process of the inferior appendage. From males of P. neiswanderi, those of P. chelatus are identified by the lack of a prominent dorsal point and deep emargination of the bodies of the pre-anal appendages, the longer and more curved basodorsal process of the inferior appendage, and the broader phallus curved less strongly ventrad.

Females of P. chelatus are readily distinguished from all others of the P. confusus species group by the central ensiform process of the internal parts of gonopods VIII in ventral view, and from all females of the P. confusus species group other than those of P. stephani by the external parts of gonopods VIII appearing digitiform in lateral view. From females of P. stephani, those of P. chelatus can be further distinguished by the subtriangular processus spermathecae vs the subovoid processus spermathecae seen in P. stephani.

Adult description

General. Length. of male 4.6–6.5 mm (mean = 5.8 mm; n = 5). Length of female 6.9 mm (n = 1).

Male genitalia (Figure 15A–E). Abdominal segment VIII annular. Terga IX and X fused, membranous, extended caudad over bases of intermediate appendages. Sternum IX subovoid in lateral view, posterior margin subtriangular. Intermediate appendages originating beneath terga IX+X and extending beyond them, curved subtly ventrad, their apices each bearing 5 small setae; in dorsal view apices proximate, subparallel. Bodies of pre-anal appendages semi-elliptical, each with slightly sinuous posterior margin, lacking posterior process; dorsal process long, curved ventrad, extending just above basodorsal process of corresponding inferior appendage, acute apically; in dorsal view slender, elongate, subparallel, apices appearing recurved mesad. Inferior appendages in lateral view each with digitiform basodorsal process erect, long, thumb-like, oriented dorsoposterad for ½ length, then curved posterad to round apex visible above main body of appendage, main body of appendage with dorsal and ventral margins subparallel for 5/6 length, then convex subapicoventrally and tapering subtly to round apex extended posterad, terminating slightly anterad to intermediate appendages; in ventral view slightly divergent, wide basally, distally tapering to round apex, basodorsal process mostly hidden by main body of inferior appendage, anterior apex projecting beyond medial margins, posterior apex projecting beyond lateral margins, in cleared specimen broad, oblong, apices round; in caudal view oblong, with medial projection round. Phallus a fully sclerotised tube, in lateral view with larger base, curved about 80° ventrad slightly beyond mid-length, apical section broad, round, internal spinules absent, internal phallic sclerite long, horizontal, subrectangular with broad anterior base tapering to narrow posterior apex.

Female genitalia (Figure 16A–B). Venter VIII in ventral view with ventral plates subparallel, narrow, semi-elliptical, round apically, covered with setae; in lateral view each tapering to round posterior apex; posterior apex of external parts of gonopods VIII in ventral view with posterior margin round; in lateral view base large, margins curving mesad for 1/3 length, then digitiform for final 2/3 length, dorsal and ventral margins parallel, extending beyond ventral plates with round apex; internal parts of gonopods VIII in ventral view visible through venter VIII even in uncleared specimen, appearing smooth, darker than surrounding tissue, with central ensiform process extending about ½ length of ventral plates, flanked by two round, thumb-like, convergent processes terminating at about 2/3 length of ventral plates; in ventral view anterior part of genital chamber apparently absent; processus spermathecae subtriangular, flat, anterior apex not extending anterad to sclerotised external part of gonopods VIII, bearing opening of ductus spermathecae.

Notes. The holotype of this species was dissected from the pupal skin, which is stored in the same vial. Unfortunately, most of the larval and pupal sclerites are missing.

Biology. Almost nothing is known of the biology of this uncommon species. Adults have been collected near clear, fast-flowing, low-order streams from March to May. The holotype was dissected from its pharate pupal skin collected in May.

Distribution (Figure 42). Alabama, Indiana, Kentucky, Missouri, Tennessee.

Polycentropus chelatus has a narrower range than most species, apparently restricted to a more central eastern Nearctic range. Despite being reported from Indiana (Waltz and McCafferty 1983), Kentucky (Etnier and Schuster 1979; Moulton and Stewart 1996; Etnier et al. 2006; Floyd et al. 2012; present study), and Missouri (Mathis and Bowles 1992; Moulton and Stewart 1996; present study), P. chelatus is not known from Illinois. If this species occurs in Illinois and awaits discovery, it is most likely to occur in the far southern portion of the state.

Material examined. Holotype: USA. Tennessee: Decatur County, Sugar Tree, along Kentucky Lake, tributary of Morgan Creek, Ross et al. coll., v-1958, 1 male, associated pupal skin (INHS Insect Collection 37,258).

Non-type material. USA. Kentucky: Madison County, Cowbell Creek, Berea College Forest, [N37°32 ʹ 38.40″, W84°13 ʹ 47.28″], Chapman and Stedenfeld coll., 23-v-2013, 1 male (BYU). Missouri: Pulaski County, M. Mathis coll., 2iv-1986, 12 males (CUAC000107333). Tennessee: Montgomery County, Piny Fork at Boiling Spring Rd., Ft. Campbell, [N36° 36 ʹ 58.75″, W87°30 ʹ 51.98″], BHB coll., 29-iv-2004, 8 males (ECC 3.415). Morgan County, Crooked Fork at Petros, Rt. 116 ′fire department̍, J.K. Moulton coll., 20-v-2006, 1 male (FAMU). 8-v-2006, 1 female (FAMU).