Schendylops ramirezi

Schendylops ramirezi is a species of soil centipede in the family Schendylidae. This centipede is notable as the species with the fewest legs recorded in the order Geophilomorpha for each sex (27 pairs of legs for males, 29 leg pairs for females). This species is also the smallest in the genus Schendylops, reaching only 7 mm in length.

Discovery
This species was first described in 2013 by the zoologist Luis Alberto Pereira of the Universidad Nacional de La Plata based on specimens collected in 1999 in Brazil. These specimens include a female holotype, five paratypes (three males and two females), and nineteen other specimens (fifteen females and four males), including five subadults and fourteen juveniles. The species is named for the arachnologist Martin Javier Ramirez of the Museo Argentino de Ciencias Naturales in Buenos Aires, who collected all the specimens. These specimens are deposited at the Museu de Zoologia da Universidade de São Paulo.

Description
This species exhibits sexual dimorphism in leg number: All seven male specimens have only 27 leg pairs, and all eighteen female specimens have only 29 pairs. The holotype female (preserved in alcohol) has a pale yellowish color and measures 7 mm in length and 0.37 mm in maximum body width. The two female paratypes range from 6.5 to 7 mm in length, whereas the three male paratypes range from 5 to 6 mm in length. The five subadults (two females and three males) measure 4.5 mm in length and the fourteen juveniles (thirteen females and one male) range from 3 to 4 mm in length. Given the small size of these tiny centipedes, the original description refers to S. ramirezi as a "dwarf species."

Only one species of soil centipede other than S. ramirezi, is known to include centipedes with only 27 pairs of legs: Schendylops oligopus. Males of the species S. oligopus have 27 or 29 leg pairs, whereas females of this species have 31 pairs. These males, however, usually have 29 leg pairs and rarely have only 27 pairs. In a large sample of 31 males, only one specimen had only 27 leg pairs.

Furthermore, only one species of soil centipede other than S. ramirez is known to include females with only 29 leg pairs: Dinogeophilus oligopodus, with 29 leg pairs in both sexes. Thus, only S. ramirezi features the minimum number of legs recorded in the order Geophilomorpha for males as well as for females. Only six species in the order Geophilomorpha, including S. ramirezi, S. oligopus, and D. oligopodus, are known to feature centipedes with only 29 leg pairs.

The species S. ramirezi shares a distinctive set of traits with several other species of Schendylops, including S. oligopus. These features include pore-fields limited to the anterior region of the body, but without a pore-field on the sternite of the first leg-bearing segment. Moreover, the fourth segment of the antenna is similar in length to the contiguous segments.

Although S. ramirez and S. oligopus share many features, including a similar number of legs, these two species also differ from one another in numerous respects. For example, whereas S. ramirezi features setae on the coxosternite of the first maxillae and a large seta in the middle of the coxosternite of the second maxillae, all these setae are absent in S. oligopus. Furthermore, while both species are small, S. oligopus is nevertheless larger than S. ramirezi: Females of the species S. oligopus can reach 10 mm in length, and males can reach 8 mm in length.

Distribution
This species is known only from the type locality (Ilha Grande) in Rio de Janeiro State in Brazil.