A dimorphic species or underestimated diversity? Pseudocellus pelaezi (Coronado Gutiérrez) (Arachnida: Ricinulei: Ricinoididae) from northeastern Mexico assessed with morphological and barcoding data

Mexico boasts the highest number of known ricinuleid species worldwide, however the diversity from North America is still poorly known. Herein, we evaluate Pseudocellus pelaezi (Coronado-Gutiérrez, 1970), a dimorphic species distributed in San Luis Potosí and Tamaulipas, northeastern Mexico. This species represents the first known dimorphic species of ricinuleids, well-documented based on morphology, ultrastructure, and genetic distance. The average intraspecific genetic distance (p-distance) at the mitochondrial cytochrome c oxidase subunit 1 (CO1) within P. pelaezi was 4.1%, whereas a much higher value of 14.6% was found between analyzed species of Pseudocellus Platnick, 1980. Although the genetic distance within the species is .4%, the morphology of primary sexual structures such as the male copulatory apparatus of leg III and the female spermathecae were strongly conserved across all the specimens. However, the morphology of a secondary sexual structure, male femora II, showed variation, with some males possessing a thin femora II (morpho 1-M1) (homeomorphic) and others with a wide femora II (morpho 2-M2) (heteromorphic). This male dimorphism, even within the same population of P. pelaezi, might be considered as a direct effect of sexual competition among males to mate with females, however more studies are needed to test this in ricinuleids. This could be done by studying and evaluating the sexual behavior in combination with the genetic evidence from specimens across several populations, offering insight into whether such dimorphism and/or genetic variation is correlated with sexual competition or represents underestimated diversity yet to be described.