Original type material lost. Collected by Cope “from Montgomery County, Virginia”.

Neotype: Male neotype (VTEC, MPE01942); 1 male from Virginia, Montgomery County, Christiansburg, Yellow Sulfur Springs Spa (37.1796, -80.3979, Elev. 607m), 30 June 2016 (Colls: P. Shorter, J. Means, V. Wong). Head and posterior body rings preserved as voucher. Collected on a hardwood log on a footpath between the old hotel gardens and an abandoned bowling alley.

Other material examined: 3 males, 3 females, details as for neotype; 109 males, 113 females, and 52 juveniles were examined from Virginia and nine other states (West Virginia, Tennessee, North Carolina, Florida, South Carolina, Alabama, Georgia, Ohio, and Kentucky), details in Suppl. material 1.

We here designate a neotype for A.corticarius because the holotype or syntypes have not been located and are presumed lost (see Material and methods section), and because our morphological studies indicate that “A.corticarius” may represent more than one species. To provide a basis for taxonomy of the group we have selected a specimen from the type locality which agrees in all details with the description given by Cope (1869).

Adult males of A.corticarius are distinct from other Andrognathus species based on the following combination of characters: Exoskeleton. Ring five with pleuroterga distinctly bilobed, papilioform (Figure 2A); lobe of anterior corner flared anteriorly, lobe of posterior corner bulging laterally, contrasting with the reduced lobes of A.hoffmani and A.grubbsi sp. n. Ring VI with metaterga singly lobed, with angulate paranota bearing a posterolaterally oriented ozopore, separating A.corticarius from A.hoffmani and A.grubbsi sp. n. in which the paranota are rounded and bear a laterally oriented ozopore (Figure 2). Paranota becoming progressively more directed posteriorly along subsequent body rings. Posterior gonopod with P6 terminating in a distally flared calyx, tip with many small serrations (Figs 6–8, Figure 9A), not spatulate as in A.hoffmani (Figure 9B) and A.grubbsi sp. n. (Figure 9C). Claw (ungulum) of P6 present, thorn-shaped, varying in size; claw not perpendicular to the shaft of the gonopod as in A.grubbsi sp. n.

Body length (BL) = 17.9 mm, head width (HW) = 0.46 mm, collum width (CW) = 0.61 mm, metazonite width at 1/4 length of body (W1) = 0.81 mm, number of podous tergites (p) = 57, number of legs (l) = 210. NCBI accession # MH282831.

Andrognathuscorticarius is known from the panhandle of Florida, north into southern Indiana and Pennsylvania (Figure 3). Variation in somatic characters of males and females is given in Table 1, and variation in gonopodal characters in Table 2. The morphology of the A6 and P6 podomeres and the claw of the P6 of the male gonopods of A.corticarius differed most across the distribution of the species (Table 2). Four individuals from the subset of geographically widespread samples differed from the neotype in two of these three characters of the male gonopods (Figs 6B, 7A, 8A, 8D); a male from Chesterfield County, South Carolina, deviates from the neotype in all three of these characters (Figure 8B).

Genetic analysis using the COI region showed relatively low variation within eastern A.corticarius (mean pairwise distance = 0.16%). The aligned COI sequences were length invariant, trivial to align, and resulted in a matrix of 605 DNA base-pairs for 14 individuals. Individuals from Boone County, West Virginia and Scioto County, Ohio had a maximum pairwise distance of 0.99% (605 bp). The maximum pairwise distances between individuals from the same locality in Montgomery Co., Virginia, was 0.17% (605 bp).

Andrognathuscorticarius is now known from Indiana, Ohio, Pennsylvania, Kentucky, West Virginia, Virginia, Tennessee, North Carolina, South Carolina, Georgia, Alabama, and Florida (Figure 3). The map assembled here extended the known range of A.corticarius northward into southwestern Ohio and southeastern Pennsylvania and synthesized and expanded distributions from the literature (Figure 3). Based on the collection dates of museum specimens, the activity period of the species appears to span March – November, with the greatest number of specimens encountered mid-summer. Individuals are often found clinging to the underside of logs in mesic deciduous forests in aggregations of millipedes, including juveniles (Figure 1B). Andrognathuscorticarius is found from elevations of 51 m to 1160 m, and infrequently as lone adults in leaf litter and in drier habitats (Figure 10).

After some specimens of A.corticarius were collected in Pulaski Co., Virginia in 2016, a male and female were observed to be coiled together at the bottom of their container (Figure 1D). Upon closer inspection, the female was coiled around a cluster of eggs, with the male on top of her. The millipedes stayed in this configuration even when removed from their container and examined for approximately 20 minutes. This is a previously unobserved behavior in the genus, which was not known to demonstrate parental care.