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The Yucatán Peninsula, Mexico is a carbonate platform well-known for extensive karst networks of densely stratified aquifer ecosystems. This aquifer supports diverse anchialine fauna, including species of the globally distributed anchialine shrimp genus Typhlatya (Atyidae). Four species (T. campecheae, T. pearsei, T. dzilamensis and T. mitchelli) are endemic to the Peninsula, of which three are federally listed in Mexico. This first integrative evaluation (i.e., molecular, morphological, broad geographic and type locality sampling, and environmental data) of Yucatán Typhlatya reveals considerable species identity conflict in prior phylogenetic assessments, broad species ranges, syntopy within cave systems and five genetic lineages (of which two are new to science). Despite sampling from the type locality of endangered T. campecheae, specimens (and molecular data) were indistinguishable from vulnerable T. pearsei. Ancestral/divergence reconstructions support convergent evolution of a low-salinity ancestor for a post-Paleogene arc Yucatán + Cuba Typhlatya clade within the anchialine Atyidae clade. A secondary adaptation for the coastal-restricted euryhaline (2–37 psu), Typhlatya dzilamensis (unknown conservation status) was identified, while remaining species lineages were low-salinity (< 5 psu) adapted and found within the meteoric lens of inland and coastal caves. This study demonstrates the need for integrative/interdisciplinary approaches when conducting biodiversity assessments in complex and poorly studied aquifers. [ABSTRACT FROM AUTHOR]

The palaemonid genus Sandyella includes S. tricornuta (Isla María Madre, Mexico), S. mclaughlinae, S. bicornuta, S. quadricornuta and S. sexicornuta (Clipperton Island, France). These species were first described in the genus Chacella based on collections of few individuals and limited to no ecological information. Sandyella was later erected to differentiate Chacella kerstitchi from Chacella tricornuta and Chacella mclaughlinae. The remaining three Chacella species (<3 mm cephalothorax length) were later also moved to Sandyella and distinguished mainly based on variation in the less than three protuberances on the cephalothorax and number of protuberances on the abdomen. Since their description from their type localities, only Sandyella tricornuta has been additionally recorded from Bahía de La Paz, Mexico. Collections done at 13 locations along the Gulf of California (2009–2010) yielded 2,905 specimens including representatives of all Sandyella species as epibionts of 57 black coral colonies Antipathes galapagensis, which prompted a closer taxonomic examination. Based on observations of live and preserved specimens, including type material, population cephalothorax size frequency and mitochondrial COI data, we inferred that all current Sandyella species (a) exhibit three protuberances on the cephalothorax; (b) cephalothorax length and number of protuberances appear to be progressive among species; (c) species exhibit high COI sequence similarity; and d) the five Sandyella species were observed cohabiting the same black coral colony. Therefore, we conclude that the five current Sandyella species are in fact distinct ontogenetic stages of a single species, S. tricornuta, and our results of a morphological Bayesian analysis led us conclude that this species belongs to the genus Sandyella rather than Chacella. [ABSTRACT FROM AUTHOR]

Sandyella tricornuta (Hendrickx, 1990) is a small (<13 mm total length), obligate and highly specific ectosymbiont of the black coral Antipathes galapagensis Deichmann, 1941 with a remarkable morphology and body coloration that resembles black coral polyps. Sandyella tricornuta population structure was investigated to infer the reproductive periods evidenced with ovigerous females from monthly collection at Espíritu Santo Island (April 2009–March 2010) and along a latitudinal gradient of six islands (24–30° N, July 2009) located along the west coast of the Gulf of California, Mexico. A total of 2,899 S. tricornuta individuals were collected from 70 colonies of A. galapagensis with a mean density of 210 inds./m3 per black coral colony. Sea floor temperature of S. tricornuta / A. galapagensis habitat seasonally ranged between 21 and 30°C. Females constituted > 60% of the entire S. tricornuta population and > 59% of the collected females were ovigerous females, suggesting active reproduction throughout the year and along the latitudinal gradient investigated. Sandyella tricornuta population density and sex ratio was similar throughout the year indicating a seasonally stable population size. Total abundance of S. tricornuta was density independent of black coral colony size and weight indicating that S. tricornuta depends on A. galapagensis , but the black coral colony can grow and develop without S. tricornuta characteristic of a commensalism ectosymbiotic association. [ABSTRACT FROM AUTHOR]