Proposed terminology in describing both internal and external male genitalia in Diapheromerini with emphasis on Pseudosermyle Caudell, 1903 (Insecta: Phasmatodea)

Stick insect systematics has been traditionally based on external morphology, which was believed to be sufficiently informative. However, molecular data repeatedly show convergence and underestimation of species diversity due, in part, to the superficiality of morphological diagnoses based on external characters. In contrast, the internal male genitalia have proved to be useful for assessing species diversity, but remain poorly studied because of their complexity and variation. Nevertheless, interest in internal male genitalia has recently increased as they provide an important number of additional characters useful to identify species for which the traditional sets of characters are insufficient. To date, the genitalia of 105 species from 55 genera belonging to 13 families are known, but comparative approaches across taxa are difficult due to different terminology. Our aim is to propose a nomenclature for the genitalia of Diapheromerini that can be used for standardized descriptions as well as for the postulation of homology assessments. We focused on Pseudosermyle , the most diverse genus in North America, which exhibits many different shapes: phasmid appearance and genitalia. We reviewed the literature on internal male genitalia in Phasmatodea and examined it, as well as the external male genitalia in different Diapheromerini species. This is the first attempt to use these structures to identify orthologues as potential homologues within Phasmatodea. We hope that our study will improve communication and promote systematic analysis of internal and external male genitalia, at least in Diapheromerini. • First attempt at setting orthologues as potential homologues within the phallic organ of Phasmatodea. • Gonopore relevance while comparing phallic organs among Phasmatodea. • Phallic organ high variation among Pseudosermyle.