Mesocyclops yutsil Reid, 1996
Taxonomic Characterization: One-eyed. Placement of the spiniform seta of leg 5 is medially rather that subterminally on the distal (exopodite) segment. There is lateral extension and rotation of the lateral spine of leg 2 exopodite segment 1. Lack of spines on pediger 5 (Fiers et al., 1996).
Disposition of Specimens: National Museum of Natural History, Smithsonian Institution, catalog numbers USNM 259843-8, 264232, 271859-61, 274244.
Ecological Classification: Stygobitic
Size: Largest female measured 0.612 mm in length; largest male 0.592 mm.
Number of Species in Genus: Numerous
Genus Range: This genus has a worldwide distribution.
Species Range: Known from Cenote Yuncu, Cenote Kambul, Cenote Mucuyche,
Cenote Mayan Blue, Cenote Najaron, Cenote 27 Steps and Grutas de Tzab-Nah,
Yucatan Peninsula, Mexico.
Closest Related Species: Closely related to M. chaci and M. reidae Petkovski, 1986.
Habitat: Freshwater and anchialine limestone caves
Ecology: Has a planktonic life in large subterranean water volumes. Collected in depths of 0-30 meters from freshwater to marine salinities. Sediments on the bottoms of the cenotes range from sand to rock to detrital organic matter. Lifestyle is omnivorous, tending toward carnivory. Additional fauna include: cyclopoids, harpacticoids, misophrioids, isopods, shrimps, ostracods, thermosbaenaceans and diaptomids (Fiers et al., 1996).
Life History: Thousands of specimens have been collected, with the majority being copepodids (at least 1,098 specimens). 87 female specimens and 5 male specimens have been collected. Egg sacs were not present on any specimens collected.
Evolutionary Origins: Along with M. chaci and Keiferiella delamarei (Lescher-Moutoué, 1971; 1976) (known from the saturated zone of a karst system in France), this species is considered a species-flock which has radiated as a specialist within a highly dynamic geomorphological environment. It is as if M. yutsil shared a cervicular living ancestor with M. chaci, but evolved for a planktonic existence in the Yucatan cenotes. It has been suggested several times that ancestral copepods were epibenthic, giving rise to planktonic forms (Fiers et al., 1996).
Conservation Status: Known from numerous freshwater and anchialine caves in Yucatan and Quintana Roo, Mexico.
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