Phylum Arthropoda Typhlatya mitchelli melanistic female showing color pattern: after Hobbs,
Typhlatya mitchelli Hobbs & Hobbs, 1976
Typhlatya mitchelli melanistic female showing color pattern: after Hobbs, 1979
Taxonomic Characterization: Translucent to white or pigmented small shrimp.
Pigment, which occurs only in individuals from some localities, appears grayish
to black or brown (Hobbs, 1979). Eyes lack facets and pigment. Rostrum does not
extend anteriorly beyond eyes.
Disposition of Specimens: National Museum of Natural History, Smithsonian Institution, holotype catalog number USNM 151904; The Museum, Texas Tech University; and Insituto de Biología, Universidad Nacional Autónoma de Mexico.
Ecological Classification: Stygobitic
Size: Total length to about 16 mm; carapace length of adult females was 3.4-4.8 mm.
Number of Species in Genus: Seventeen, all stygobitic
Species Range: This species is known from numerous caves and cenotes in
the Coastal Plain from the states of Quintana Roo and Yucatan, Mexico.
Closest Related Species: T. mitchelli is intermediate, both in morphology and in geographic position, between the Caribbean species with a short rostrum (from Cuba and Mona) and the seemingly disjunct species from the Galapagos (Hobbs & Hobbs, 1976).
Habitat: Freshwater cave pools
Ecology: According to Hobbs (1979:622), "In all localities shrimps were living in lentic situations varying from very small shallow (less than 0.3 m depth) pools to extensive underground lakes (greater than 2.0 m depth). Generally the pools were in total darkness, but T. mitchelli occurs in entrance areas that receive direct light from the surface. Substrates of the pools consisted of guano, silt, organic debris, rocks and combinations thereof. Shrimp were found on the substrate, "hanging" from submerged walls along the edges of lakes, free-swimming, and among dense, branched root systems hanging down from the roof of cenotes." Often occurs with the more abundant T. pearsei.
Life History: Nothing is known of the life history. Sexual dimorphism noted in the second pereiopods of the females (Hobbs & Hobbs, 1976). Holthius (1977) described the appendix masculina of the male second pleopod.
Evolutionary Origins: Of the seventeen 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 along the Coastal Plain of the Yucatan Peninsula. Classified as endangered by the NOM-059-ECOL-2001 "Norma Oficial Mexicana".
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