We describe the parthenita colonies, soldier rediae, reproductive rediae, cercariae, metacercariae, and sexual adults of Cloacitrema michiganensis McIntosh, 1938 and Cloacitrema kurisi n. sp. using material from natural and experimental infections and molecular-genetic analyses. Cloacitrema kurisi, a “pseudo-cryptic” species, was previously pooled with C. michiganensis in research involving the guild of trematodes infecting the California horn snail, Cerithideopsis californica (Haldeman, 1840), as a first intermediate host. Our morphological data suggest that C. kurisi contaminated an earlier description of the C. michiganensis life cycle based on that same snail host. Our descriptions of all life stages use material originating from naturally infected, lab-maintained horn snails from San Diego, California. By repeatedly shedding cercariae from specific, labeled snails, we obtained material for experimental infections, developmental studies, and genetics. In all cases, these data were matched to individual first-intermediate host colonies. These same colonies were finally dissected to describe the morphology, behavior, and demographics of reproductive and soldier rediae. Metacercaria descriptions came from cercariae shed and encysted in the laboratory; we also document a metacercaria developmental time series for each species. We experimentally exposed final host chickens (Gallus gallus domesticus) and ducks (Anas platyrhynchos domesticus) to metacercariae per cloaca; we successfully obtained and described sexual adults only from the chickens. Both cytochrome c oxidase subunit 1 (COI) and 28S phylogenetic analyses corroborated that these are 2 Cloacitrema species. As indicated in its original description, C. michiganensis adults can be readily distinguished from other Cloacitrema species by the combination of their inter-cecal uterus; small, oval pharynx; large, equatorial ventral sucker; and the presence of inter-testicular space. The C. kurisi adult stage can be distinguished from other Cloacitrema species by the combination of its extra-cecal, post-testicular uterus; particularly large, round pharynx; the complete absence of an esophagus; and the presence of inter-testicular space. We use our morphometric data to provide an emended diagnosis for the genus Cloacitrema. There are now 10 formally named species of Cloacitrema, 4 of which have had their first intermediate host stages described.

The sucking lice (Anoplura: Psocodea: Insecta) parasitize mammals, exclusively consuming blood, which does not contain sufficient quantities of B vitamins to support louse development. Lice are dependent on maternally inherited endosymbiotic bacteria, which can synthesize B vitamins and make them available to the louse. Although most louse species parasitize 1 mammal species, lice occasionally colonize a different mammal species. Despite endosymbiotic bacteria being essential for louse development, little is known about the impact, if any, of a louse colonizing a new mammal species on the louse's endosymbiotic bacteria. To address this knowledge gap, we sought to examine genomic diversity in maternally inherited and host-beneficial endosymbiotic bacteria in sucking lice following the likely colonization of a new host. Here, we examined the genomes of endosymbiotic bacteria, Candidatus Riesia pediculicola, from the human head louse, Pediculus humanus. Pediculus humanus (and their endosymbiotic bacteria) are found on humans and South American primate species. The association of P. humanus with humans predates the appearance of modern humans; however, P. humanus appears to have colonized South American primates more recently (likely following the arrival of humans in South America). We examined the genome of Candidatus Riesia from P. humanus isolated from humans (Homo sapiens) and South American black howler monkeys (Alouatta caraya). Here, we find that endosymbiont diversity in lice collected from black howler monkeys included one-half of all known haplogroups described from lice collected from humans. Furthermore, the endosymbiont haplotypes identified from lice on the black howler monkeys reflect the haplotype diversity of endosymbionts present in lice parasitizing humans in the same geographic region. It is not known if the genetic diversity in the endosymbionts of P. humanus parasitizing the black howler monkey is the result of the ongoing movement of lice from humans to black howler monkeys or from a single host switch involving a genetically diverse population of endosymbionts.