''Tylobolus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of millipedes in the order

Spirobolida Spirobolida is an order of "round-backed" millipedes containing approximately 500 species in 12 families. Its members are distinguished by the presence of a "pronounced suture that runs "vertically down the front of the head". Most of the spec ...

with seven known

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

found in western North America. It is in the family Spirobolidae, and is the type genus of the subfamily Tylobolinae. The genus was named by

Orator F. Cook Orator Fuller Cook Jr. (May 28, 1867 – April 23, 1949) was an American botanist, entomologist, and agronomist, known for his work on cotton and rubber cultivation and for coining the term "speciation" to describe the process by which new species ...

in 1904.

Description

Species of ''Tylobolus'' are medium to large millipedes ranging from long and wide, with females attaining larger sizes than males. They are cylindrical, or nearly so, and possess 40 to 54 segments (body rings) as adults. Body color ranges from black to reddish brown, the posterior margin of each ring may be faintly or strongly colored in red or yellow. The body rings are mostly smooth or with a very fine texture. The two eyes, each composed of 27-50 ocelli in a patch or "ocular field", are widely separated, with more than twice the width of a patch between them.

Species

All species of ''Tylobolus'' occur on the

Pacific Slope The Pacific Slope describes geographic regions in North American, Central American, and South American countries that are west of the continental divide and slope down to the Pacific Ocean. In North America, the Rocky Mountains mark the eastern bo ...

of North America, ranging from

Washington state Washington (), officially the State of Washington, is a state in the Pacific Northwest region of the Western United States. Named for George Washington—the first U.S. president—the state was formed from the western part of the Washington ...

Baja California Baja California (; 'Lower California'), officially the Free and Sovereign State of Baja California ( es, Estado Libre y Soberano de Baja California), is a state in Mexico. It is the northernmost and westernmost of the 32 federal entities of Mex ...

, Mexico. Only one species occurs east of the

Sierra Nevada The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primarily ...

mountains. ''T. uncigerus'' is the northernmost species, ranging to just north of the

Columbia River The Columbia River (Upper Chinook: ' or '; Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, C ...

in Washington. The southernmost species, ''T. claremontus'', ranges from

Los Angeles Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world' ...

and western Riverside County to northern Baja. Most of the Pacific species have small geographic ranges and do not overlap. The only species east of the Sierra Nevada is ''T. utahensis'', which occurs in the

Mojave Desert The Mojave Desert ( ; mov, Hayikwiir Mat'aar; es, Desierto de Mojave) is a desert in the rain shadow of the Sierra Nevada mountains in the Southwestern United States. It is named for the indigenous Mojave people. It is located primarily in ...

.. An additional species, "''T. fredericksoni''", was previously thought to occur in

Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the ...

and

Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the southwe ...

, but its existence is dubious, and may be attributable to '' Narceus americanus'', a spirobolid common in the eastern U.S. Since no specimens of "''T. fredericksoni''" have been discovered since 1949 and the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

s are highly fragmented and equivocal, the species is considered a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...

'' or doubtful name.

Classification

''Tylobolus'' may be one of the most advanced genera of the family Spirobolidae, in terms of a number of traits it possesses that are absent or poorly developed in other spirobolids. ''Tylobolus'' is the type genus of the subfamily Tylobolinae which includes one other genus, '' Hiltonius'', occurring from Southern California into Mexico. Of the two, ''Tylobolus'' is thought to be the more advanced due to more complex genital morphology, and a prominently hooked projection of the third pair of legs in males. Tylobolinae is thought to be more derived than the other subfamily, Spirobolinae. The family Spirobolidae itself is thought to be the most primitive family of the order

References

External links

''Tylobolus''
on BugGuide {{Taxonbar, from=Q4248784 Millipedes of North America Spirobolida