Buotus carolinus Chamberlin 1940

Shear, William A., 2009, Buotidae, a new family for the minute North American milliped Buotus carolinus (Chamberlin) 1940 (Diplopoda, Chordeumatida, Striarioidea), Zootaxa 2290, pp. 41-49 : 44-48

Buotus carolinus Chamberlin 1940

Figs. 1–10 , Map 1

Buotus carolinus Chamberlin 1940 , p. 58; Shear, 1981, p. 18; 1998, p. 92.

The original description of Buotus carolinus lacked any diagnostic details, and indeed the species was placed far from its proper position in the Chordeumatidae—in the colobognath family Polyzoniidae , where it resided for more than 40 years until I restudied it ( Shear 1981). I revisited the species in 1998 based on the same specimens and added more details regarding the gonopods ( Shear & Hubbard 1998). However, the animals are so small (smaller mature males may be only 2 mm long or less) and the gonopods correspondingly minute, that an examination using a scanning electron microscope (SEM) revealed many new details.

Chamberlin (1940) described the species as having a single ocellus, which I found to be a rather poorly defined pigment spot, deep-lying in the head ( Shear 1981). The SEM reveals that there is no external expression of this spot whatsoever and no cuticular lens—the characteristic sculpture of the head is continuous over the position of the pigment spot ( Figs. 2 , 3 ). The mandible has a posterior serrate margin on the cardo, which just can be seen in Fig. 3 between the first leg and the anterior margin of the collum. The first leg is not reduced in size. The seminal ducts of the male open through pores in the second coxae, as in all chordeumatidans yet studied. The sculpture or ornament of the collum and metaterga differs from the simple acute tubercles of the head ( Figs. 2 , 3 cf. 4, 6) and consists of a series of irregularly arranged, minute ridges on raised mounds. On the sides of the mounds and scattered among them are morate (mulberry-shaped, from morum, L., a mulberry) tubercles. At the posterior margin of the metazonite, the ridges and tubercles are abruptly replaced with a few rows of sharp-pointed, recurved teeth above the shallowly serrate limbus. The teeth of the limbus serrations are created by small ridges. On more posterior segments, the ridges become more closely spaced and crowd out most of the interspersed morate tubercles. The segmental setae are very small, only about 20µm long, and hardly detectable using optical microscopy or even at low magnifications under the SEM (try to find them on Fig. 4 ). It may have been the apparent absence of these setae, characteristic of Chordeumatida , that caused Chamberlin not to consider that order as a place for Buotus . Nevertheless, they are present ( Fig. 7 ); each seta arises from an elongate, tubular socket and presents a single, spiral twist. The tip of the seta is divided into five or six short processes, which give the whole a remarkable resemblance to a human arm and hand! The sculpture of the epiproct ( Fig. 5 ) more closely resembles that of the head. The spinnerets arise, as in striariids (Shear 2008) from beneath the posterior margin of the epiproct; above each spinneret is an emargination in the epiproct which gives it a three-lobed appearance (also as in striariids).

The gonopods ( Figs. 8–10 ) are small even for the size of the animal and the tips of the flattened, bladelike angiocoxites extend posteriorly between the ninth leg coxites, so that their tips rest in the coxal glands of the tenth legpair. Further details of the gonopods can be seen in Shear (1981) and Shear and Hubbard (1998). The ninth legs of males are typical of striarioids, with a well-sclerotized coxosternum ( Fig. 8 ); from the coxal portion arise long, sinuate coxites with broad tips, that arch over the recumbent gonopods and probably serve to protect them ( Figs. 8, 9 ). The telopodites are heavily sclerotized and set with acute tubercles and setae. Except for gland openings, the tenth coxae are not modified or enlarged, but the eleventh coxae have large, blunt posterior processes.

Natural history and distribution of B. carolinus . Collections of B. carolinus have rarely been made by hand-searching, though R. L. Hoffman, W. A. Shear and R. M. Shelley found three specimens sorting leaf litter on Brush Mountain, Montgomery Co., Virginia, in March, 1976. All of the new records below are from Berlese samples of deciduous leaf litter, several from rhododendron, but also from litter under oak, cherry or beech. At least two localities are beside streams. Even using the Berlese technique, most samples consist of a single individual, rarely up to 3– 5 specimens. Buotus specimens are easily overlooked; the species is a strong contender for the title of the world’s smallest milliped, with males usually less than 3 mm, and some scarcely 2 mm long. Females rarely exceed 4 mm even if well-extended. In addition, my recent collections from Quaker Field Branch, Campbell Co., Virginia, came from the deepest layers of duff, where litter and debris had accumulated to a depth of nearly 20 cm. Most of the specimens have been taken at elevations at or exceeding 3000 feet (1022 m), though the type locality in is the North Carolina piedmont at an elevation of about 350 ft. (106 m).

It is curious that all records aside from the type locality are from the Appalachians of Virginia and West Virginia. Despite extensive collecting by R. M. Shelley and others in the North Carolina piedmont, the species has not been found there since Causey’s collection of a single female in 1939. In his 1940 paper, most of the specimens Chamberlin reports on are indeed from the Duke Forest, but a few came from other localities in the North Carolina Appalachians. It is possible the Buotus specimens were only assumed to be from the Duke Forest, but in fact came from one of the Appalachian localities. This hypothesis is weakened by the failure of anyone to find the species in the North Carolina mountains, where extensive collecting has been done by many people over the seven decades since 1939.

New records: See Map 1, which also includes the records I published in 1982. All collections by R. L. Hoffman unless otherwise noted; all specimens from Virginia Museum of Natural History. VIRGINIA: Bedford Co.: Apple Orchard Mountain, rhododendron litter Berlese, 4000’ asl, 15 June 1997, female. Bland Co.: west side of Big Walker Mountain, 6 km E of Sharon Springs, 3000’ asl, 9 May 1981, 3 males. Grayson Co.: south slope of Whitetop Mountain, Forest Road 600, streamside litter Berlese, 5000’ asl, 23 December 1984, 2 females; Whitetop Mountain, in beech woods, 5000’ asl, 18 November 1993 – 16 March 1994, VMNH Survey, female. Patrick Co.: 1.4 mi W of Claudville on Rt. 773, rhododendron litter Berlese, 18 December 2006, male; Quaker Field Branch bridge on US 58 near Vesta, oak, rhododendron litter Berlese, 23 May 2007, W. A. Shear, 3 males, 4 females; 23 August 2009, W. A. Shear, female. Roanoke Co.: crest of Poor Mountain, leaf litter Berlese, 3750’ asl, 30 October 1999, female. Tazewell Co: east slope of Beartown Mountain, Burkes Garden, 4000’ asl, 17 May 1981, male.

MAP 1. Distribution of Buotus carolinus . The type locality in Durham Co., North Carolina, is not shown but is about 110 miles (177 km) southeast of the nearest other localities, in Patrick Co., Virginia.

Figures

FIGURES 1, 2. Buotus carolinus. 1. Mature female specimen, lateral view. 2. Head of male specimen, dorsofrontal view.

FIGURES 3 – 6. Buotus carolinus. 3. Head and collum of female specimen, lateral view. 4. Segments 10 – 12 of female specimen, dorsal view, anterior above. 5. Epiproct of female specimen, ventral view. 6. Sculpture of metatergite near limbus, dorsal view.

FIGURES 7 – 10. Buotus carolinus. 7. Lateral segmental seta from metatergite 12, dorsal view. 8 – 10 Gonopods (blue) and ninth legpair (red), in situ in segment seven. 8. Posterior view. 9. Anterior view. 10. Ventral view.