| Apterourus | |
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| Genus: | Apterourus Loomis, 1966 |
| Type species | |
| Apterourus horizontalis Loomis, 1966 | |
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Apterourus is a genus of millipedes in the monotypic family Apterouridae, which contains no other genera. [1] The genus belongs to the suborder Striariidea and the superfamily Striarioidea. Adult individuals possess exactly 30 body segments, counting the collum as the first segment and the telson as the last. [2] The genus is endemic to California, United States, and currently comprises three described species. [3]
The genus Apterourus and the family Apterouridae were established by the American myriapodologist H. F. Loomis in 1966. [4] The description was based on a single male specimen of the type species, Apterourus horizontalis, collected in 1929 at Cajon Pass in San Bernardino County, California.
The genus remained monotypic for several decades. A second species, Apterourus serratus, was described in 2003, [5] followed by a third species, Apterourus palomar, described in 2025. [6]
Species of Apterourus are restricted to California and exhibit a highly localized distribution in coastal and montane regions. Apterourus horizontalis is known only from its type locality at Cajon Pass in San Bernardino County. Apterourus serratus was described from Monterey County, California and represents the northernmost confirmed occurrence of the genus, [5] while A. palomar extends the known range southward to Mount Palomar in San Diego County, California. [6]
All known specimens have been collected from moist forested habitats, typically within leaf litter, soil, or beneath decaying wood. The genus is considered rare, with very few specimens recorded despite targeted collecting in suitable habitats. [5] [6]
Millipedes of the genus Apterourus are small to medium-sized members of the order Chordeumatida. Adults consistently possess 30 body segments, a fixed segment number characteristic of the family Apterouridae. [2] Members of the genus display diagnostic features of the suborder Striariidea, including modified male ninth legs and distinctive gonopod structure.
Within the superfamily Striarioidea, Apterouridae is distinguished by a collum that is narrower than the head, distinctly bilobed paranota, and strongly reduced male ninth legs that are concealed beneath the anterior gonopods. [7]
Species of Apterourus are distinguished primarily by details of male gonopod morphology and by differences in segment ornamentation. Apterourus serratus is characterized by serrated structural features, whereas A. palomar differs in gonopod configuration and other morphological details while remaining broadly similar to its congeners. [5] [6]