''Tylobolus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

millipede Millipedes (originating from the Latin , "thousand", and , "foot") are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derive ...

s in the order

Spirobolida Spirobolida is an Order (biology), order of "round-backed" millipedes containing approximately 500 species in 12 family (biology), families. Its members are distinguished by the presence of a "pronounced Suture (anatomy), suture that runs "verti ...

with seven known

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

found in western North America. It is in the family Spirobolidae, and is the

type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearin ...

of the subfamily Tylobolinae. The genus was named by Orator F. Cook 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 A simple eye or ocellus (sometimes called a pigment pit) is a form of eye or an optical arrangement which has a single lens without the sort of elaborate retina that occurs in most vertebrates. These eyes are called "simple" to distinguish the ...

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 of North America, ranging from

Washington state Washington, officially the State of Washington, is a state in the Pacific Northwest region of the United States. It is often referred to as Washington State to distinguish it from the national capital, both named after George Washington ...

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

, 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 primari ...

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

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

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

Los Angeles Los Angeles, often referred to by its initials L.A., is the List of municipalities in California, most populous city in the U.S. state of California, and the commercial, Financial District, Los Angeles, financial, and Culture of Los Angeles, ...

and western

Riverside County Riverside County is a county located in the southern portion of the U.S. state of California. As of the 2020 census, its population was 2,418,185, making it the fourth-most populous county in California and the 10th-most populous in the Unit ...

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 (; ; ) is a desert in the rain shadow of the southern Sierra Nevada mountains and Transverse Ranges in the Southwestern United States. Named for the Indigenous peoples of the Americas, indigenous Mohave people, it is located pr ...

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

Kansas Kansas ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the west. Kansas is named a ...

and

Nebraska Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...

, 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 (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

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 ...

'' 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

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 BugGuide (or BugGuide.net) is a website and online community of naturalists, both amateur and professional, who share observations of arthropods such as insects, spiders, and other related creatures. The website consists of informational guide p ...

{{Authority control Millipedes of North America Spirobolida