Taxonomic Characterization: Small, light, whitish shrimp, somewhat opaque but not transparent; eyes lack facets and pigment. Carapace
lacking spines. Rostrum extending anteriorly to at least midlength of second podomere of antennular pedulcle. Uniformity in the development
of the exopod of the fifth pereiopod; it is exceedingly small. Dactyl of fifth pereiopod with more than 40 denticulate spines on flexor surface
(Hobbs and Hobbs, 1976).
Disposition of Specimens: National Museum of Natural History, Smithsonian Institution, and The Museum, Texas Tech University.
Ecological Classification: Stygobitic
Size: To about 17 mm in total length. Carapace length of males to 3.8 mm; of females to 5.2 mm (Hobbs & Hobbs, 1976).
Number of Species in Genus: Seventeen, all stygobitic
T. pearsei is the most widely distributed atyid on the Yucatan Peninsula, being known from 21 locales in the Northeastern and Northwestern Coastal Plain, the Sierra de Ticul and the Sierra de Bolonchen physiographic districts in the states of Campeche, Quintana Roo and Yucatan (Hobbs, 1979).
Closest Related Species: T. pearsei belongs to a group in which the rostrum extends beyond the eyes. This group includes Typhlatya species from Bermuda, Ascension Island, Cuba and Campeche (Mexico).
Habitat: Freshwater cave pools
Ecology: According to Hobbs (1979), "This species is found in lentic habitats ranging from small pools (less than 0.5 m in depth) to deep lakes greater than 8 m). These bodies of water are generally floored with silt or bat guano....Typhlatya pearsei is generally found in total darkness but occasionally individuals are seen in entrance areas where pools receive either direct or indirect light from the surface." Dissolved oxygen levels in pools containing this shrimp are as low as 0.78 mg /l or about 10% saturation (Hall, 1936).
Life History: Of the 220 specimens examined by Hobbs (1979), 88% were females, 5% males and 6% juveniles. Sexual dimorphism noted in the second pereiopod of both males and females. Ovigeous females have not been reported for this shrimp (Hobbs & Hobbs, 1977).
Evolutionary Origins: Of the eleven species in the genus, six (from the Galapagos Islands, Bahamas, Bermuda, Ascension Island, Yucatan and the Caicos Islands) inhabit brackish or marine waters, while the remainder are found in freshwater habitats. According to Iliffe (1986:7), "species within the genus appear to have evolved from an open water marine ancestor in the Atlantic which spread westward through the Caribbean into the Pacific with prevailing currents before the closure of the Panama land bridge." Iliffe et al. (1983) suggested an origin of the genus on submerged and emergent seamounts associated with the Mid-Atlantic Ridge during the separation of the American and African continental masses.
Sanz and Platvoet (1995) believe that the occurrence of the genus in Europe links the origin of the genus Typhlatya to the Tethys Sea. The ancestor was probably a marine, coastal shrimp inhabiting low latitude seas. Maximal development of the ancestral range probably occurred in the Late Cretaceous (about 90 MYA). The full opening of the Atlantic and the end of global Tethyan currents divided its range into three populations: European, Mid-Atlantic Ridge and Central American. Central American populations were further subdivided by plate tectonics into Yucatan, Antilles and Galapagos populations. For unknown reasons, the ancestral marine populations disappeared, leaving only those species that had earlier entered the cave environment. Absence of clear morphological patterns within the recent species may be due to the early timing of isolation between and within lineages.
Both T. pearsei and T. mitchelli show identical degrees of eye reduction suggesting that they started their cavernicolous evolution at the same time (Wilkens, 1982).
Conservation Status: Found in numerous freshwater caves and cenotes throughout the Yucatan Peninsula. Classified as endangered by the NOM-059-ECOL-2001 "Norma Oficial Mexicana".
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