Two species of fossil polydesmidan millipedes (Diplopoda: Polydesmida) embedded in amber are described from Miocene strata near Simojovel, in the Chiapas Highlands, Mexico. Maatidesmus paachtun
gen. et sp. nov., placed into Chelodesmidae Cook, 1895, and Anbarrhacus adamantis
gen. et sp. nov., assigned in the family Platyrhacidae Pocock, 1895. Morphological data from fossil specimens have been recovered using 3D X-ray micro-computed tomography and regular to infrared-reflected microscopy. Both fossil species are recognizable as new primarily but not exclusively, by collum margin modification and remarkable paranotal and metatergite dorsal sculpture.
An inventory of fossil millipedes (class Diplopoda) and centipedes (class Chilopoda) from Miocene Chiapas amber, Mexico, is presented, with the inclusion of new records. For Diplopoda, 34 members are enumerated, for which 31 are described as new fossil records of the orders Siphonophorida Newport, 1844, Spirobolida Bollman, 1893, Polydesmida Leach, 1895, Stemmiulida Pocock, 1894, and the superorder Juliformia Attems, 1926. For Chilopoda 8 fossils are listed, for which 3 are new records of the order Geophilomorpha Pocock, 1895 and 2 are of the order Scolopendromorpha Pocock, 1895.
Running title: Circadian rhythms in cave-dwelling fish Astyanax
Abstract:Circadian regulation has a profound adaptive meaning in timing the best performance of biological functions in a cyclic niche. However, in cave-dwelling animals (troglobiotic) a lack of photic cyclic environment may represent a disadvantage for persistence of circadian rhythms. There are different populations of cave-dwelling fish Astyanax mexicanus in caves of the Sierra El Abra, Mexico, with different evolutive history. In the present work we report that fish collected from El Sótano la Tinaja show circadian rhythms of swimming activity in laboratory conditions. Rhythms observed in some of the organisms entrain to either continuous light-dark cycles or discrete skeleton photoperiods tested. Our results indicate that circadian rhythm of swimming activity and their ability to entrain in discrete and continuous photoperiods persist in some organisms that might represent one of the oldest populations of cave-dwelling Astyanax mexicanus in the Sierra
A new fossil species of pyrgodesmid millipede (Polydesmida: Pyrgodesmidae) placed in the genus Myrmecodesmus Silvestri, 1910 is described. The type materials are two amber inclusions, male and female specimens that come from Miocene strata in Chiapas, Mexico. Myrmecodesmus antiquus sp. nov. has collum with 10 dorsal tubercles; without porosteles or ozopores; legs of the rings 2–9 with a short projection on the prefemur in both the female and male. Myrmecodesmus antiquus sp. nov is the first fossil record of the genus Myrmecodesmus. This is a New World taxon that belongs to the pantropical family Pyrgodesmidae. Thus, Myrmecodesmus antiquus sp. nov expands the range of the genus to the Miocene tropics in Middle America.
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