Polycentropus thaxtoni Hamilton and Holzenthal, 1986

Orfinger, Alexander Benjamin, 2023, Taxonomic revision of the Polycentropus confusus species group (Trichoptera: Polycentropodidae), Journal of Natural History 57 (41 - 44), pp. 1825-1916 : 1893-1896

Polycentropus thaxtoni Hamilton and Holzenthal

( Figures 34 , 53 )

Polycentropus thaxtoni Hamilton and Holzenthal, 1986: 163–165 , figs. 1–7, J; type locality ′ Georgia: Crawford County: Spring Creek above pond at Camp Eunice, approx. five miles SSE of Roberta (ca. 32°40 ʹ N, 83°59 ʹ W)̍ ( USNM).

Polycentropus thaxtoni Armitage and Hamilton, 1990 : figs. A–F, J.

Diagnosis. Males of Polycentropus thaxtoni are most similar to those of P. chelatus , P. confusus , P. floridensis , P. neiswanderi and P. pentus , from which they can be distinguished by the following combination of characters: long, dorsomesally excavated ventral portions of the inferior appendages with subrectangular apices, the deep dorsal emarginations of the bodies of the pre-anal appendages, and the lack of a basoventral swelling of the phallus.

Adult description

General. Length. of male 6.0– 6.9 mm (mean = 6.3 mm; n = 4).

Male genitalia ( Figure 34A–E ). Abdominal segment VIII annular. Terga IX and X fused, membranous, extended caudad over bases of intermediate appendages. Sternum IX subovoid in lateral view, ventral half of posterior margin slightly sinuous, dorsal half of posterior margin concave. Intermediate appendages originating beneath terga IX+X and extending beyond them, curved slightly ventrad, their apices each bearing 3 small setae; in dorsal view apices proximate, subparallel. Bodies of pre-anal appendages each with subtriangular posteroventral corner, deep dorsal emargination, posterodorsal margin round; dorsal process long, curved roughly 90° ventrad, apex aligned with posterodorsal margin of head of basodorsal process of corresponding inferior appendage, acute apically; in dorsal view slender, subparallel, apices strongly incurvate. Inferior appendages in lateral view each with lobate basodorsal process erect with moderately short neck and broad head round dorsally and projecting caudad with its round apex visible above main body of appendage, main body of appendage with dorsal and ventral margins subparallel along length, dorsal margin curved slightly dorsad at subrectangular apex, surface with dorsomesal excavation along length; in ventral view subparallel, margins subparallel basally, mesal margin curving outward beyond mid-length, lateral margin curving inward apically, appendage distally tapering to round apex, apices oriented caudolaterally, distal half of basodorsal process exposed beyond lateral margins of main body of inferior appendage, medial projection mostly behind main body of inferior appendage, in cleared specimen elongate, with apex of medial round projection exposed mesally; in caudal view oblong, with wide base and slender posteromesal projection round. Phallus a fully sclerotised tube, in lateral view with larger base, curved about 20° ventrad slightly beyond mid-length, apical section rectangular, internal spinules absent, internal phallic sclerite long, horizontal, semi-elliptical.

Female genitalia. Unknown.

Larva. Unknown.

Pupa. Unknown.

Biology. Virtually nothing is known of the biology of this species. Adults have been collected in May and September using UV light traps. The type locality is a second-order blackwater stream with abundant aquatic macrophytes, allochthonous plant matter, and some deadwood with a sand substrate matrix. This locality sits on private property in a rural area with little development and is densely forested, appearing relatively undisturbed. This is promising when considering that this Spring Creek site is also the type locality and only known location for Beraea gorteba Ross, 1944 ( Beraeidae ) and Hydroptila roberta Hamilton and Holzenthal, 1986 ( Hydroptilidae ). The single specimen of P. thaxtoni collected in Alabama was taken adjacent to a cool, clear, first-order stream with rock and sand substrate.

Distribution ( Figure 53 ). USA: Alabama, Georgia.

Until recently, Polycentropus thaxtoni was known from only its type locality of Spring Creek in Crawford County, Georgia. Orfinger and Moulton (2021) reported a single male specimen from an unnamed stream in Dekalb County, Alabama .

Material examined. Holotype: USA. Georgia: Crawford County, Spring Creek above pond at Camp Eunice, approximately 5 miles south–south-east of Roberta, UV light, S.W. Hamilton and R. W. Holzenthal coll., 8-ix-1983, 1 male (USNMENT01507917) . Paratypes: USA. Georgia: Crawford County, Spring Creek above pond at Camp Eunice, approx. 5 miles SSE of Roberta , [N32°040 ̍, W83°059 ̍], Hamilton and Holzenthal coll., 8-ix-1983, 1 male ( CUAC000016084 ) . Spring Creek above pond at Camp Eunice, approximately 5 miles south–south-east of Roberta, UV light, S.W. Hamilton and R.W. Holzenthal coll., 29-ix-1983, 1 male (USNMENT01507920).

Non-type material. USA. Alabama: Dekalb County, unnamed stream crossing Rd 05 c. 220 m south Rd 09, 390 masl, [N34°27 ʹ 01.42″, W85°34 ʹ 57.66″], J. Robinson and C.R. Parker coll., 11-v-2007, 1 male ( LIRI 1098 ) .

Figures

Figure 34. Polycentropus thaxtoni Hamilton and Holzenthal, 1986, male genitalia (holotype). A. left lateral (with phallus removed); B. dorsal; C, segment IX and inferior appendages, ventral; D. phallus, left lateral; E. dorsobasal process of right inferior appendage, caudal.

Figure 53. Known Canadian province and US state distribution of Polycentropus thaxtoni Hamilton and Holzenthal, 1986, as indicated by grey shading.