Stenelmis hollandi White and Lenat

White, David S. & Lenat, David A., 2015, Stenelmis hollandiWhite and Lenat (Coleoptera: Elmidae), a New Species of Riffle Beetle from the Little River, North Carolina, USA, The Coleopterists Bulletin 69 (4), pp. 723-726 : 723-725

Stenelmis hollandi White and Lenat , new species ( Figs. 1–2 )

General description as in Fig. 1 , except where noted, based on cleaned specimens. All specimens were collected by David A. Lenat.

Description. Size: Total length including head 2.42–2.70 mm; width 0.95–1.02 mm. Because the head can be partially retracted into the pronotum, the combined length of the pronotum and elytra may be a better measure of length as was done by Sanderson (1938). Combining just the pronotal and elytral measurements, total length 2.39–2.60 mm. Females on average slightly larger than males. Head: Antennae and palpi yellow to flavotestaceous. Length of each antenna 0.65–0.75 mm and equal to width of pronotum; granulations between eyes similar in size and appearance to those on pronotum. Pronotum: Length 0.70–0.80 mm; width 0.65–0.72 mm. Color dark brown, darker on lateral margins, basomesal triangle darker brown than most of dorsal surface; pronotum subparallel but not distinctly divergent at apex, abruptly constricted before middle, widest at middle, then tapering to slight sinuation at basal point; median sulcus shallow and not pronounced; lateral and posterior tubercles not distinctly raised; granulations weak and widely spaced. Elytra: Length 1.62–1.85 mm, females slightly longer than males on average; width 0.97–1.02 mm. Color brown, darker laterally on some specimens, moderately shiny in cleaned specimens; each elytron with a single longitudinal testaceous vitta not overlapping umbone, occupying area between the lateral carina and discal costa on the 3 rd interval, vitta extending to near apex of elytra, may be slightly constricted or clouded medially; elytral punctures large and deep, decreasing slightly in size toward the apex. Venter: Uniformly brown to light brown; apical abdominal emargination approximately equal to width of last tarsomere. Legs: Tarsi yellow to flavotestaceous similar to antennae; femora and tibiae darker. Apices of femora and tibiae testaceous. Femora, tibiae, and tarsomeres of all legs of approximately equal length, 0.52–0.62 mm; male mesotibial spinous ridge present; last tarsal segment distinctly dilated in distal third; last tarsomere longer than tarsomeres 1–4 combined, claws robust; granules of femora and tarsi separated by about their diameters. Male genitalia: Total length 0.50–0.52 mm; width 0.14–0.16 mm; parameres shorter than penis, rounded at tips ( Fig. 2 ); penis noticeably constricted in middle; lateral processes on penis prominent, widest in basal third, tapering toward tip of penis.

Types. Holotype, male; Lower Little River , Harnett County, North Carolina, USA, at State Road 2031, 23 June / 2 August 2011, D. A. Lenat . Paratypes: 10 males and 10 females with same information as type. Holotype along with five male and five female paratypes to be deposited at United States National Museum of Natural History , Washington, DC. Another 10 paratypes will be deposited at the Sam Noble Oklahoma Museum of Natural History , The University of Oklahoma, Norman, OK, USA. The remaining specimens, including the additional 19 that were measured, are in the collections of the first author .

Diagnosis. It is not possible at this time to alter existing keys ( Sanderson 1938; Brown 1972; White 1982a; Ciegler 2003) to include S. hollandi without restructuring many of the couplets. Indeed, the genus is in need of examination using molecular techniques before any revision occurs. Stenelmis hollandi may be anatomically separated from similar species such as Stenelmis decorata Sanderson , Stenelmis bicarinata LeConte , and Stenelmis convexula Sanderson by the shape of the male genitalia and the combination of its small size, distinct, single, testaceous vitta on each elytron that does not overlap the umbone, distinctly dilated fifth tarsomere, and mesotibial ridge in males. Additionally, it has yellowish palpi, antennae, and tarsi.

So far, this species is known only from the Little River in North Carolina. It is quite possible, however, that it will be discovered in additional Sandhills rivers when more systems are surveyed, as has been true for other Stenelmis described from seemingly restricted locations in the Carolinas (White and Brown 1976; White 1982b; Ciegler 2003). There are at least four other species of Stenelmis known from the Little River ( Stenelmis antennalis Sanderson , Stenelmis lignicola Schmude and Barr , Stenelmis morsei White , and Stenelmis xylonastis Schmude and Brown ), and perhaps there are more that have yet to be identified, but S. hollandi appears to be the most common Stenelmis in the river. Other elmids captured at the time of the collection of S. hollandi included Macronychus glabratus (Say) and Ancyronyx variegata (Germar) .

Much of the Lower Little River is designated as High Quality Water. The river at State Road 2023 (Moore County), about 15 km upstream from the type locality, usually receives an excellent bioclassification based on high EPT (Ephemeroptera/ Plecoptera /Trichoptera) taxa richness (31–35 species) and the presence of many highly intolerant species (North Carolina Division of Water Quality 2004). Other invertebrate species that are endemic to the Lower Little River include the plecopterans Perlesta leathermani Kondratieff and Zeullig , Perlesta bjostadi Kondratieff and Lenat , and Haploperla fleeki Kondratieff, Kirchener, and Lenat ( Kondratieff et al. 2005, 2006). Steve Fend and the second author also have found two stillundescribed species of aquatic worms ( Lumbriculidae ) in this section of the river.

The Little River originates in the Piedmont ecoregion of North Carolina but flows mainly through the Sandhills ecoregion (Griffith et al. 2002). Mean stream width is usually about 15– 20 m. Although much of the area has a sand/gravel substrate, sites with S. hollandi , including the type locality, usually include some rubble and boulder habitat. The lower section of the river has very steep banks (gorge-like) with bedrock areas along the bank. Stenelmis hollandi was found primarily in fastflowing areas ( Fig. 3 ) on rocks and gravel. Stenelmis morsei was most often collected in gravel, while the other elmids from the Little River drainage are associated with submerged wood. The number of Stenelmis species present poses the potential for resource and habitat partitioning in the Little River. While elmids may not always be the best descriptor of water quality (White and Roughley 2008), the inclusion of this new species along with endemic stoneflies and generally high diversity helps to illustrate that the Little River drainage continues to have excellent water quality and a variety of productive habitats.

Figures

Fig. 1. Dorsal aspect of Stenelmis hollandi female showing general features of the pronotum and elytra. Photograph courtesy of Eric Fleek, North Carolina Division of Water Resources.

Fig. 2. Dorsal view of Stenelmis hollandi male genitalia. Parameres are splayed more than they would appear naturally.

Fig. 3. Typical Stenelmis hollandi riffle habitat on the Lower Little River, North Carolina.