New penis characters to distinguish between two American Artemia species

Abstract

We studied characteristics of distal retractile penis structures for two recognized species from the New World: A. franciscana, and A. persimilis. Artemia franciscana was characterized by the absence of spine-like outgrowths, while A. persimilis had several spine-like outgrowths at the base of the eversible penis. The distal part of everted penis of A. franciscana is a simple tube armed near its base with only an occasional wart-like protuberance tipped with a single thin spine and ending in a finger-like tip. The retractile penis in A. persimilis was armed with two different groups of conical spine-like outgrowths. The first row of three to four spine-like outgrowths was localized at the junction of the basal and the distal part in a lateral–dorsal position. The second row contained three or more irregularly positioned conical spines localized on the base of the distal part in a lateral–dorsal position. We observed no finger-like tip on the distal penis of A. persimilis. There were also wart-like protuberances tipped with a single thin spine on the base of the distal penis. Some individuals of A. persimilis showed a single hook-shaped spine located in a lateral–ventral position. Our present study confirms that, for species in which the antennal characters are not informative enough, as in the case of Artemia, male genital characters are useful to distinguish not only between genera but also between species when the distal part of the penis is considered. Characters of the distal eversible penis add new valuable information for phylogenetic research.