Brachoria Chamberlin 1939

Introduction

The apheloriine millipede genus Brachoria comprises 34 species distributed throughout the southeastern U.S. Appalachian Mountains.  Brachoria is the third largest (in terms of species) millipede genus in the U.S., Cleidogona and Pseudotremia are the largest with 80 and 47.  Members of this genus are blind and produce cyanide (like all millipedes in the order Polydesmida).  They are large (4-6 cm in length) and display conspicuous aposematic coloration in yellow, red, orange and violet.  Many Brachoria species participate in Müllerian mimicry rings with co-occurring Apheloriini, in particular with species in the genus Apheloria.

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Considerable color and pattern variation between morphs of a single species, Brachoria dentata. © Paul Marek

Characteristics

• Large (4-6 cm in length), broad, “flat-backed” millipedes.  Bright aposematic coloration in yellow, orange, red, violet that commonly mimics other sympatric apheloriine genera.  Brachoria individuals frequently mimic the yellow and black spots or alternating yellow and black bands of Apheloria. 

• Collum with carinae present on anterolateral margins, absent medially; carinae rarely completely absent.

• Distinct cingulum present (cg). 

Other apheloriine genera lack a cingulum, except for individuals in the genus Appalachioria, see below for distinguishing characters between individuals in the genera Brachoria and Appalachioria.

• Acropodite occasionally bulky (in 10 out of 34 species); width greater than tibia on leg pair nine (species with bulky gonopods: B. splendida, B. blackmountainensis, B. calceata, B. campcreekensis, B. cumberlandmountainensis, B. kentuckiana, B. laminata, B. plecta, B. sheari, and B. viridicolens). 

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Scanning electron micrographs of Brachoria left male gonopods, labeled with key features (ca = cannula, cg = cingulum, pp = prefemoral process, ps = prostatic groove), left: bulky gonopod from Brachoria splendida, middle: narrow gonopod from Brachoria hendrixsoni, right: acropodite from B. hendrixsoni, magnified view of cingulum and prostatic groove (scale bars = 1 mm). © 2010 Paul Marek

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Illustration of Brachoria initialis left male gonopod, color-coded by region.  The gonopod comprises the acropodite (light gray), prefemur (medium gray), and coxa (dark gray).  Dashed lines indicate junctions between (moving distally from the prefemur) the precingular region, postcingular region, and apex (ap = acropodite, ax = acropodite apex, cx = coxa, pf = prefemur, post-cg = post-cingular region of acropodite, pre-cg = precingular region of acropodite). © 2010 Paul Marek 

*Note: Individuals of Brachoria may be confused with Apheloria and Appalachioria, but can be distinguished from Apheloria by the presence of the following characters (viewed with a 20X loupe): Acropodite with cingulum (cg).  Acropodite, when viewed ventrally C- or D-shaped, acropodal apex not coiled, or overlapping prefemoral region, not circular.  Individuals of Brachoria can be distinguished from Appalachioria by the presence of the following characters (viewed with a 20X loupe): Collum with carinae present on anterolateral margins, absent medially.  Caudolateral corners of paranota usually rounded cephalically on anterior body rings (1 – 4) and acute, projecting caudally (beyond paranotal caudal edge) throughout posterior body rings (11 – 19); not rounded on all segments (1 – 19) as in Appalachioria.

Habitat

Brachoria are predominately found in Appalachian mixed mesophytic deciduous forests (B. cedra often occur in cedar glades) beneath decomposing leaf material on the forest floor.  Individuals are less frequently encountered in Tsuga canadensis and Rhododendron coves.

Distribution

Predominately distributed in the Valley and Ridge and Cumberland Plateau provinces from southern West Virginia to northeastern Kentucky, south to eastern Tennessee and southwestern Virginia.  The range of the genus extends into the historically unglaciated southeastern corner of Indiana, northeastern Mississippi and Alabama, and northwestern Georgia.  The species B. initialis is broadly distributed in the coastal plain in Alabama, Mississippi and Louisiana (extending west of the Mississippi River).

References

Hoffman R.L. 1971. Millipeds of the genus Brachoria from southwestern Virginia (Polydesmida: Xystodesmidae). Radford Rev. 25: 83–99.

Hoffman R.L. 1971. Millipeds of the genus Brachoria from southwestern Virginia (Polydesmida: Xystodesmidae). Rad. Rev. 25: 83-99.

Keeton W.T. 1959. A revision of the millipede genus Brachoria (Polydesmida: Xystodesmidae). Proc. U.S. Nat. Mus. 109: 1-58.

Keeton W.T. 1965. Descriptions of three new species of Brachoria, with notes on established species (Diplopoda, Polydesmida, Xystodesmidae). Proc. Biol. Soc. Wash. 78: 225-240.

Marek P.E., Bond J.E. 2006. Phylogenetic systematics of the colorful, cyanide-producing millipedes of Appalachia (Polydesmida, Xystodesmidae, Apheloriini) using a total evidence Bayesian approach. Mol. Phylogenet. Evol. 41: 704–729.

Marek P.E., Bond J.E. 2007. A reassessment of apheloriine millipede phylogeny: additional taxa, Bayesian inference, and direct optimization (Polydesmida: Xystodesmidae). Zootaxa 1610: 27–39.

Marek P.E., Bond J.E. 2009. A Müllerian mimicry ring in Appalachian millipedes. Proc. Nat. Acad. Sci. USA 106: 9755-9760.

Marek P.E. 2010. A revision of the Appalachian millipede genus Brachoria Chamberlin, 1939 (Polydesmida: Xystodesmidae: Apheloriini). Zool. J. Linn. Soc. 159: 817-889.

Shelley R.M. 1979. The status of Sigmoria gracilipes Chamberlin, with remarks on the milliped genus Brachoria (Polydesmida: Xystodesmidae). Fla. Entomol. 62: 220–223.